Find whether it is File or Directory.

Here is a Java Program for Using directories.

import java.io.File;

class DirList {
  public static void main(String args[]) {
    String dirname = "/java";
    File f1 = new File(dirname);

    if (f1.isDirectory()) {
      System.out.println("Directory of " + dirname);
      String s[] = f1.list();

      for (int i=0; i < s.length; i++) {
        File f = new File(dirname + "/" + s[i]);
        if (f.isDirectory()) {
          System.out.println(s[i] + " is a directory");
        } else {
          System.out.println(s[i] + " is a file");
        }
      }
    } else {
      System.out.println(dirname + " is not a directory");
    }
  }
}

Output of Above Java Program
Directory of /java
COPYRIGHT is a directory
DevelopmentTutorial.com is a directory
Index.php is a file
Language-Tutorial is a directory

[ Read More ]

Demonstrate File by Getting the Name and other Information of File

Here is a Java Program to Demonstrate File.

import java.io.File;

class FileDemo {
  static void p(String s) {
    System.out.println(s);
  }

  public static void main(String args[]) {
    File f1 = new File("/java/COPYRIGHT");
    p("File Name: " + f1.getName());
    p("Path: " + f1.getPath());
    p("Abs Path: " + f1.getAbsolutePath());
    p("Parent: " + f1.getParent());
    p(f1.exists() ? "exists" : "does not exist");
    p(f1.canWrite() ? "is writeable" : "is not writeable");
    p(f1.canRead() ? "is readable" : "is not readable");
    p("is " + (f1.isDirectory() ? "" : "not" + " a directory"));
    p(f1.isFile() ? "is normal file" : "might be a named pipe");
    p(f1.isAbsolute() ? "is absolute" : "is not absolute");
    p("File last modified: " + f1.lastModified());
    p("File size: " + f1.length() + " Bytes");
  }
}

Output of Above Java Program
File Name: COPYRIGHT
Path: \java\COPYRIGHT
Abs Path: C:\java\COPYRIGHT
Parent: \java
exists
is writeable
is readable
is
might be a named pipe
is not absolute
File last modified: 1329568044285
File size: 0 Bytes

[ Read More ]

Demonstrate Currency by gettimg a Locale Currency Symbol

Here is a Java Program to Demonstrate Currency.

import java.util.*;

class CurDemo {
  public static void main(String args[]) {
    Currency c;

    c = Currency.getInstance(Locale.US);

    System.out.println("Symbol: " + c.getSymbol());
    System.out.println("Default fractional digits: " +
                       c.getDefaultFractionDigits());
  }
}

Output of Above Java Program
Symbol: $
Default fractional digits: 2

[ Read More ]

Demonstrate Timer and TimerTask

Here is a Java Program to Demonstrate Timer and TimerTask.

import java.util.*;

class MyTimerTask extends TimerTask {
  public void run() {
    System.out.println("Timer task executed.");
  }
}

class TTest {
  public static void main(String args[]) {
    MyTimerTask myTask = new MyTimerTask();
    Timer myTimer = new Timer();

    /* Set an initial delay of 1 second,
       then repeat every half second.
    */
    myTimer.schedule(myTask, 1000, 500);
    
    try {
      Thread.sleep(5000);
    } catch (InterruptedException exc) {}

    myTimer.cancel();
  }
}

Output of Above Java Program
Timer task executed.
Timer task executed.
Timer task executed.
Timer task executed.
Timer task executed.
Timer task executed.
Timer task executed.
Timer task executed.
Timer task executed.

[ Read More ]

Demonstrate the Observable class and the Observer interface.

Here is a Java Program to Demonstrate the Observable class and the Observer interface.

import java.util.*;

// This is the observing class.
class Watcher implements Observer {
  public void update(Observable obj, Object arg) {
    System.out.println("update() called, count is " +
                       ((Integer)arg).intValue());
  }
}

// This is the class being observed.
class BeingWatched extends Observable {
  void counter(int period) {
    for( ; period >=0; period--) {
      setChanged();
      notifyObservers(new Integer(period));
      try {
        Thread.sleep(100);
      } catch(InterruptedException e) {
        System.out.println("Sleep interrupted");
      }
    }
  }

}

class ObserverDemo {
  public static void main(String args[]) {
    BeingWatched observed = new BeingWatched();
    Watcher observing = new Watcher();

    /* Add the observing to the list of observers for
       observed object.  */
    observed.addObserver(observing);

    observed.counter(10);
  }
}

Output of Above Java Program
update() called, count is 10
update() called, count is 9
update() called, count is 8
update() called, count is 7
update() called, count is 6
update() called, count is 5
update() called, count is 4
update() called, count is 3
update() called, count is 2
update() called, count is 1
update() called, count is 0

[ Read More ]

Demonstrate Random Gaussian values

Here is a Java Program to Demonstrate random Gaussian values.

import java.util.Random;

class RandDemo {
  public static void main(String args[]) {
    Random r = new Random();
    double val;
    double sum = 0;
    int bell[] = new int[10];

    for(int i=0; i<100; i++) {
      val = r.nextGaussian();
      sum += val;
      double t = -2;
      for(int x=0; x<10; x++, t += 0.5)
        if(val < t) {
          bell[x]++;
          break;
        }
    }
    System.out.println("Average of values: " +
                        (sum/100));

    // display bell curve, sideways
    for(int i=0; i<10; i++) {
      for(int x=bell[i]; x>0; x--)
        System.out.print("*");
      System.out.println();
    }
  }
}

Output of Above Java Program
Average of values: 0.13714951059857725
*
*********
****
************
*****************
*****************
***********************
*********
*****
*

[ Read More ]

Java Program to Demonstrate Calendar

Here is a Java Program to Demonstrate Calendar

import java.util.Calendar;

class CalendarDemo {
  public static void main(String args[]) {
    String months[] = {
             "Jan", "Feb", "Mar", "Apr", 
             "May", "Jun", "Jul", "Aug",
             "Sep", "Oct", "Nov", "Dec"};

    // Create a calendar initialized with the
    // current date and time in the default
    // locale and timezone.
    Calendar calendar = Calendar.getInstance();

    // Display current time and date information.
    System.out.print("Date: ");
    System.out.print(months[calendar.get(Calendar.MONTH)]);
    System.out.print(" " + calendar.get(Calendar.DATE) + " ");
    System.out.println(calendar.get(Calendar.YEAR));

    System.out.print("Time: ");
    System.out.print(calendar.get(Calendar.HOUR) + ":");
    System.out.print(calendar.get(Calendar.MINUTE) + ":");
    System.out.println(calendar.get(Calendar.SECOND));

    // Set the time and date information and display it.
    calendar.set(Calendar.HOUR, 10);
    calendar.set(Calendar.MINUTE, 29);
    calendar.set(Calendar.SECOND, 22);

    System.out.print("Updated time: ");
    System.out.print(calendar.get(Calendar.HOUR) + ":");
    System.out.print(calendar.get(Calendar.MINUTE) + ":");
    System.out.println(calendar.get(Calendar.SECOND));
  }
}

Output of Above Java Program
Date: Feb 18 2012
Time: 5:40:59
Updated time: 10:29:22

[ Read More ]

Demonstrating BitSet for convert into AND, OR and XOR

Here is a Java Program to Demonstrating the BitSet

import java.util.BitSet;

class BitSetDemo {
  public static void main(String args[]) {
    BitSet bits1 = new BitSet(16);
    BitSet bits2 = new BitSet(16);

    // set some bits
    for(int i=0; i<16; i++) {
      if((i%2) == 0) bits1.set(i);
      if((i%5) != 0) bits2.set(i);
    }

    System.out.println("Initial pattern in bits1: ");
    System.out.println(bits1);
    System.out.println("\nInitial pattern in bits2: ");
    System.out.println(bits2);

    // AND bits
    bits2.and(bits1);
    System.out.println("\nbits2 AND bits1: ");
    System.out.println(bits2);

    // OR bits
    bits2.or(bits1);
    System.out.println("\nbits2 OR bits1: ");
    System.out.println(bits2);

    // XOR bits
    bits2.xor(bits1);
    System.out.println("\nbits2 XOR bits1: ");
    System.out.println(bits2);
  }
}

Output of Above Java Program
Initial pattern in bits1:
{0, 2, 4, 6, 8, 10, 12, 14}

Initial pattern in bits2:
{1, 2, 3, 4, 6, 7, 8, 9, 11, 12, 13, 14}

bits2 AND bits1:
{2, 4, 6, 8, 12, 14}

bits2 OR bits1:
{0, 2, 4, 6, 8, 10, 12, 14}

bits2 XOR bits1:
{}

[ Read More ]

A simple telephone number database that uses a property list.

Here is a Java Program to A simple telephone number database that uses a property list.

import java.io.*;
import java.util.*;

class Phonebook {
  public static void main(String args[]) 
    throws IOException
  {
    Properties ht = new Properties();
    BufferedReader br =
      new BufferedReader(new InputStreamReader(System.in));
    String name, number;
    FileInputStream fin = null;
    boolean changed = false;

    // Try to open phonebook.dat file.
    try {
      fin = new FileInputStream("phonebook.dat");
    } catch(FileNotFoundException e) {
      // ignore missing file
    }

    /* If phonebook file already exists, 
       load existing telephone numbers. */
    try {
      if(fin != null) {
        ht.load(fin);
        fin.close();
      }
    } catch(IOException e) {
      System.out.println("Error reading file.");
    }

    // Let user enter new names and numbers.
    do {
      System.out.println("Enter new name" + 
                         " ('quit' to stop): ");
      name = br.readLine();
      if(name.equals("quit")) continue;

      System.out.println("Enter number: ");
      number = br.readLine();

      ht.put(name, number);
      changed = true;
    } while(!name.equals("quit"));

    // If phone book data has changed, save it.
    if(changed) {
      FileOutputStream fout = new FileOutputStream("phonebook.dat");

      ht.store(fout, "Telephone Book");    
      fout.close();
    }

    // Look up numbers given a name.
    do {
      System.out.println("Enter name to find" +
                         " ('quit' to quit): ");
      name = br.readLine();
      if(name.equals("quit")) continue;

      number = (String) ht.get(name);
      System.out.println(number);
    } while(!name.equals("quit"));
  }
}

Output of Above Java Program
sanjay
Enter number:
9977777516
Enter new name ('quit' to stop):
Hell
Enter number:
442312345348
Enter new name ('quit' to stop):
ASDF
Enter number:
4647511366489
Enter new name ('quit' to stop):
quit
Enter name to find ('quit' to quit):
sanjay
9977777516
Enter name to find ('quit' to quit):
asdf
null
Enter name to find ('quit' to quit):
ASDF
4647511366489
Enter name to find ('quit' to quit):
quit

[ Read More ]

Demonstrate a Property list

Here is a Java Program to Demonstrate a Property list.

import java.util.*;
 
class PropDemo {
  public static void main(String args[]) {
    Properties capitals = new Properties();
    Set states;
    String str;

    capitals.put("Illinois", "Springfield");
    capitals.put("Missouri", "Jefferson City");
    capitals.put("Washington", "Olympia");
    capitals.put("California", "Sacramento");
    capitals.put("Indiana", "Indianapolis");

    // Show all states and capitals in hashtable.
    states = capitals.keySet(); // get set-view of keys
    Iterator itr = states.iterator();

    while(itr.hasNext()) {
      str = (String) itr.next();
      System.out.println("The capital of " +
                         str + " is " +
                         capitals.getProperty(str)
                         + ".");
    }

    System.out.println();

    // look for state not in list -- specify default
    str = capitals.getProperty("Florida", "Not Found");
    System.out.println("The capital of Florida is "
                       + str + ".");
  }
}

Output of Above Java Program
The capital of Missouri is Jefferson City.
The capital of Illinois is Springfield.
The capital of Indiana is Indianapolis.
The capital of California is Sacramento.
The capital of Washington is Olympia.

The capital of Florida is Not Found.

[ Read More ]

Demonstrate the Stack Class

Here is a Java Program to Demonstrate the Stack class.

import java.util.*;
 
class StackDemo {
  static void showpush(Stack st, int a) {
    st.push(new Integer(a));
    System.out.println("push(" + a + ")");
    System.out.println("stack: " + st);
  }

  static void showpop(Stack st) {
    System.out.print("pop -> ");
    Integer a = (Integer) st.pop();
    System.out.println(a);
    System.out.println("stack: " + st);
  }

  public static void main(String args[]) {
    Stack st = new Stack();

    System.out.println("stack: " + st);
    showpush(st, 42);
    showpush(st, 66);
    showpush(st, 99);
    showpop(st);
    showpop(st);
    showpop(st);
    try {
      showpop(st);
    } catch (EmptyStackException e) {
      System.out.println("empty stack");
    }
  }
}

Output of Above Java Program
stack: Stack@19821f
push(42)
stack: Stack@19821f
push(66)
stack: Stack@19821f
push(99)
stack: Stack@19821f
pop -> 99
stack: Stack@19821f
pop -> 66
stack: Stack@19821f
pop -> 42
stack: Stack@19821f
pop -> Stack underflow.
0
stack: Stack@19821f

[ Read More ]

Demonstrate various Vector operations

Here is a Java Program to Demonstrate various Vector operations.

import java.util.*;

class VectorDemo {
  public static void main(String args[]) {

    // initial size is 3, increment is 2
    Vector v = new Vector(3, 2);

    System.out.println("Initial size: " + v.size());
    System.out.println("Initial capacity: " +
                       v.capacity());

    v.addElement(new Integer(1));
    v.addElement(new Integer(2));
    v.addElement(new Integer(3));
    v.addElement(new Integer(4));

    System.out.println("Capacity after four additions: " +
                       v.capacity());
    v.addElement(new Double(5.45));
    System.out.println("Current capacity: " +
                       v.capacity());
    v.addElement(new Double(6.08));
    v.addElement(new Integer(7));

    System.out.println("Current capacity: " +
                       v.capacity());
    v.addElement(new Float(9.4));
    v.addElement(new Integer(10));

    System.out.println("Current capacity: " +
                       v.capacity());
    v.addElement(new Integer(11));
    v.addElement(new Integer(12));


    System.out.println("First element: " +
                       (Integer)v.firstElement());
    System.out.println("Last element: " +
                       (Integer)v.lastElement());

    if(v.contains(new Integer(3)))
      System.out.println("Vector contains 3.");

    // enumerate the elements in the vector.
    Enumeration vEnum = v.elements();

    System.out.println("\nElements in vector:");
    while(vEnum.hasMoreElements())
      System.out.print(vEnum.nextElement() + " ");
    System.out.println();
  }
}

Output of Above Java Program
Initial size: 0
Initial capacity: 3
Capacity after four additions: 5
Current capacity: 5
Current capacity: 7
Current capacity: 9
First element: 1
Last element: 12
Vector contains 3.

Elements in vector:
1 2 3 4 5.45 6.08 7 9.4 10 11 12

[ Read More ]

Demonstrate various algorithms like Sort, Shuffle and reverseOrder

Here is a Java Program to Demonstrate various algorithms.

import java.util.*;

class AlgorithmsDemo {
  public static void main(String args[]) {

    // Create and initialize linked list
    LinkedList ll = new LinkedList();
    ll.add(new Integer(-8));
    ll.add(new Integer(20));
    ll.add(new Integer(-20));
    ll.add(new Integer(8));
    
    // Create a reverse order comparator
    Comparator r = Collections.reverseOrder();

    // Sort list by using the comparator
    Collections.sort(ll, r);

    // Get iterator
    Iterator li = ll.iterator();

    System.out.print("List sorted in reverse: ");    
    while(li.hasNext())
      System.out.print(li.next() + " ");
    System.out.println();

    Collections.shuffle(ll);

    // display randomized list
    li = ll.iterator();
    System.out.print("List shuffled: ");    
    while(li.hasNext())
      System.out.print(li.next() + " ");
    System.out.println();

    System.out.println("Minimum: " + Collections.min(ll));    
    System.out.println("Maximum: " + Collections.max(ll));        
  }
}

Output of Above Java Program
List sorted in reverse: 20 8 -8 -20
List shuffled: -20 20 -8 8
Minimum: -20
Maximum: 20

[ Read More ]

Use a Comparator to Sort Accounts by Last Name

Here is a Java Program to Use a comparator to sort accounts by last name.

import java.util.*;

// Compare last whole words in two strings.
class TComp implements Comparator {
  public int compare(Object a, Object b) {
    int i, j, k;
    String aStr, bStr;

    aStr = (String) a;
    bStr = (String) b;

    // find index of beginning of last name
    i = aStr.lastIndexOf(' ');
    j = bStr.lastIndexOf(' ');

    k = aStr.substring(i).compareTo(bStr.substring(j));
    if(k==0) // last names match, check entire name
      return aStr.compareTo(bStr);
    else
      return k;
  }

  // no need to override equals
}

class TreeMapDemo2 {
  public static void main(String args[]) {
    // Create a tree map
    TreeMap tm = new TreeMap(new TComp());
    
    // Put elements to the map
    tm.put("John Doe", new Double(3434.34));
    tm.put("Tom Smith", new Double(123.22));
    tm.put("Jane Baker", new Double(1378.00));
    tm.put("Tod Hall", new Double(99.22));
    tm.put("Ralph Smith", new Double(-19.08));

    // Get a set of the entries
    Set set = tm.entrySet();

    // Get an iterator
    Iterator itr = set.iterator();

    // Display elements
    while(itr.hasNext()) {
      Map.Entry me = (Map.Entry)itr.next();
      System.out.print(me.getKey() + ": ");
      System.out.println(me.getValue());
    }
    System.out.println();

    // Deposit 1000 into John Doe's account
    double balance =  ((Double)tm.get("John Doe")).doubleValue();
    tm.put("John Doe", new Double(balance + 1000));
    System.out.println("John Doe's new balance: " +
      tm.get("John Doe"));
  }
}

Output of Above Java Program
Jane Baker: 1378.0
John Doe: 3434.34
Tod Hall: 99.22
Ralph Smith: -19.08
Tom Smith: 123.22

John Doe's new balance: 4434.34

[ Read More ]

Demonstrate TreeMap by Adding Elements

Here is a Java Program to Demonstrate TreeMap

import java.util.*;

class TreeMapDemo {
  public static void main(String args[]) {

    // Create a tree map
    TreeMap tm = new TreeMap();
    
    // Put elements to the map
    tm.put("John Doe", new Double(3434.34));
    tm.put("Tom Smith", new Double(123.22));
    tm.put("Jane Baker", new Double(1378.00));
    tm.put("Tod Hall", new Double(99.22));
    tm.put("Ralph Smith", new Double(-19.08));

    // Get a set of the entries
    Set set = tm.entrySet();

    // Get an iterator
    Iterator i = set.iterator();

    // Display elements
    while(i.hasNext()) {
      Map.Entry me = (Map.Entry)i.next();
      System.out.print(me.getKey() + ": ");
      System.out.println(me.getValue());
    }
    System.out.println();

    // Deposit 1000 into John Doe's account
    double balance =  ((Double)tm.get("John Doe")).doubleValue();
    tm.put("John Doe", new Double(balance + 1000));
    System.out.println("John Doe's new balance: " +
      tm.get("John Doe"));
  }
}

Output of Above Java Program
Jane Baker: 1378.0
John Doe: 3434.34
Ralph Smith: -19.08
Tod Hall: 99.22
Tom Smith: 123.22

John Doe's new balance: 4434.34

[ Read More ]

Demonstrate HashMap by Adding Elements

Here is a Java Program to Demonstrate HashMap

import java.util.*;

class HashMapDemo {
  public static void main(String args[]) {

    // Create a hash map
    HashMap hm = new HashMap();
    
    // Put elements to the map
    hm.put("John Doe", new Double(3434.34));
    hm.put("Tom Smith", new Double(123.22));
    hm.put("Jane Baker", new Double(1378.00));
    hm.put("Tod Hall", new Double(99.22));
    hm.put("Ralph Smith", new Double(-19.08));

    // Get a set of the entries
    Set set = hm.entrySet();

    // Get an iterator
    Iterator i = set.iterator();

    // Display elements
    while(i.hasNext()) {
      Map.Entry me = (Map.Entry)i.next();
      System.out.print(me.getKey() + ": ");
      System.out.println(me.getValue());
    }
    System.out.println();

    // Deposit 1000 into John Doe's account
    double balance =  ((Double)hm.get("John Doe")).doubleValue();
    hm.put("John Doe", new Double(balance + 1000));
    System.out.println("John Doe's new balance: " +
      hm.get("John Doe"));
  }
}

Output of Above Java Program
John Doe: 3434.34
Tom Smith: 123.22
Jane Baker: 1378.0
Tod Hall: 99.22
Ralph Smith: -19.08

John Doe's new balance: 4434.34

[ Read More ]

A Simple Mailing List using LinkedList

Here is a Java Program to Demonstrate simple mailing list Using LinkedList.

import java.util.*;

class Address {
  private String name;
  private String street;
  private String city;
  private String state;
  private String code;

  Address(String n, String s, String c, 
          String st, String cd) {
    name = n;
    street = s;
    city = c;
    state = st;
    code = cd;
  }

  public String toString() {
    return name + "\n" + street + "\n" +
           city + " " + state + " " + code;
  }
}

class MailList {
  public static void main(String args[]) {
    LinkedList ml = new LinkedList();
    
    // add elements to the linked list
    ml.add(new Address("J.W. West", "11 Oak Ave",
                       "Urbana", "IL", "61801"));
    ml.add(new Address("Ralph Baker", "1142 Maple Lane",
                       "Mahome", "IL", "61853"));
    ml.add(new Address("Tom Carlton", "867 Elm St",
                       "Champaign", "IL", "61820"));

    Iterator itr = ml.iterator();
    while(itr.hasNext()) {
      Object element = itr.next();
      System.out.println(element + "\n");
    }
    System.out.println();
  }
}

Output of Above Java Program
J.W. West
11 Oak Ave
Urbana IL 61801

Ralph Baker
1142 Maple Lane
Mahome IL 61853

Tom Carlton
867 Elm St
Champaign IL 61820

[ Read More ]

Demonstrate TreeSet to Add Elements

Here is a Java Program to Demonstrate TreeSet.

import java.util.*;

class TreeSetDemo {
  public static void main(String args[]) {
    // Create a tree set
    TreeSet ts = new TreeSet();
    
    // Add elements to the tree set
    ts.add("C");
    ts.add("A");
    ts.add("B");
    ts.add("E");
    ts.add("F");
    ts.add("D");

    System.out.println(ts);
  }
}

Output of Above Java Program
[A, B, C, D, E, F]

[ Read More ]

Demonstrate HashSet to Add Element

Here is a Java Program to Demonstrate HashSet.

import java.util.*;

class HashSetDemo {
  public static void main(String args[]) {
    // create a hash set
    HashSet hs = new HashSet();
    
    // add elements to the hash set
    hs.add("B");
    hs.add("A");
    hs.add("D");
    hs.add("E");
    hs.add("C");
    hs.add("F");

    System.out.println(hs);
  }
}

Output of Above Java Program
[D, E, F, A, B, C]

[ Read More ]

Linked List to Add and Remove Element

Here is a Java Program to Demonstrate the Linked List.

import java.util.*;

class LinkedListDemo {
  public static void main(String args[]) {
    // create a linked list
    LinkedList ll = new LinkedList();
    
    // add elements to the linked list
    ll.add("F");
    ll.add("B");
    ll.add("D");
    ll.add("E");
    ll.add("C");
    ll.addLast("Z");
    ll.addFirst("A");

    ll.add(1, "A2");

    System.out.println("Original contents of ll: " + ll);

    // remove elements from the linked list
    ll.remove("F");
    ll.remove(2);

    System.out.println("Contents of ll after deletion: "
                       + ll);

    // remove first and last elements
    ll.removeFirst();
    ll.removeLast();

    System.out.println("ll after deleting first and last: "
                       + ll);

    // get and set a value
    Object val = ll.get(2);
    ll.set(2, (String) val + " Changed");

    System.out.println("ll after change: " + ll);
  }
}

Output of Above Java Program
Original contents of ll: [A, A2, F, B, D, E, C, Z]
Contents of ll after deletion: [A, A2, D, E, C, Z]
ll after deleting first and last: [A2, D, E, C]
ll after change: [A2, D, E Changed, C]

[ Read More ]

Convert an ArrayList into an array

Here is a Java Program to Convert an ArrayList into an array.

import java.util.*;

class ArrayListToArray {
  public static void main(String args[]) {
    // Create an array list
    ArrayList al = new ArrayList();
    
    // Add elements to the array list
    al.add(new Integer(1));
    al.add(new Integer(2));
    al.add(new Integer(3));
    al.add(new Integer(4));

    System.out.println("Contents of al: " + al);
 
    // get array
    Object ia[] = al.toArray();
    int sum = 0;

    // sum the array
    for(int i=0; i<ia.length; i++)
      sum += ((Integer) ia[i]).intValue();

    System.out.println("Sum is: " + sum);
  }
}

Output of Above Java Program
Contents of al: [1, 2, 3, 4]
Sum is: 10

[ Read More ]

Demonstrate Run-Time Type Information

Here is a Java Program to Demonstrate Run-Time Type Information.

class TestClone implements Cloneable {
  int a;
  double b;

  // This method calls Object's clone().
  TestClone cloneTest() {
    try {
      // call clone in Object.
      return (TestClone) super.clone();
    } catch(CloneNotSupportedException e) {
      System.out.println("Cloning not allowed.");
      return this;
    }
  }
}
class X {
  int a;
  float b;
}

class Y extends X {
  double c;
}

class RTTI {
  public static void main(String args[]) {
    X x = new X();
    Y y = new Y();
    Class clObj;

    clObj = x.getClass(); // get Class reference
    System.out.println("x is object of type: " +
                       clObj.getName());

    clObj = y.getClass(); // get Class reference
    System.out.println("y is object of type: " +
                       clObj.getName());
    clObj = clObj.getSuperclass();
    System.out.println("y's superclass is " +
                       clObj.getName());
  }
}

class CloneDemo {
  public static void main(String args[]) {
    TestClone x1 = new TestClone();
    TestClone x2;

    x1.a = 10;
    x1.b = 20.98;

    x2 = x1.cloneTest(); // clone x1

    System.out.println("x1: " + x1.a + " " + x1.b);
    System.out.println("x2: " + x2.a + " " + x2.b);
  }
}

Output of Above Java Program
x is object of type: X
y is object of type: Y
y's superclass is X

[ Read More ]

Demonstrate the clone() method

Here is a Java Program to Demonstrate the clone() method

class TestClone implements Cloneable {
  int a;
  double b;

  // This method calls Object's clone().
  TestClone cloneTest() {
    try {
      // call clone in Object.
      return (TestClone) super.clone();
    } catch(CloneNotSupportedException e) {
      System.out.println("Cloning not allowed.");
      return this;
    }
  }
}

class CloneDemo {
  public static void main(String args[]) {
    TestClone x1 = new TestClone();
    TestClone x2;

    x1.a = 10;
    x1.b = 20.98;

    x2 = x1.cloneTest(); // clone x1

    System.out.println("x1: " + x1.a + " " + x1.b);
    System.out.println("x2: " + x2.a + " " + x2.b);
  }
}

Output of Above Java Program
x1: 10 20.98
x2: 10 20.98

[ Read More ]

Demonstrate totalMemory(), freeMemory() and gc()

Here is a Java Program to Demonstrate totalMemory(), freeMemory() and gc().

class MemoryDemo {
  public static void main(String args[]) {
    Runtime r = Runtime.getRuntime();
    long mem1, mem2;
    Integer someints[] = new Integer[1000];

    System.out.println("Total memory is: " +
                       r.totalMemory());

    mem1 = r.freeMemory();
    System.out.println("Initial free memory: " + mem1);
    r.gc();
    mem1 = r.freeMemory();
    System.out.println("Free memory after garbage collection: "
                       + mem1);

    for(int i=0; i<1000; i++)
      someints[i] = new Integer(i); // allocate integers

    mem2 = r.freeMemory();
    System.out.println("Free memory after allocation: "
                       + mem2);
    System.out.println("Memory used by allocation: "
                       + (mem1-mem2));

    // discard Integers
    for(int i=0; i<1000; i++) someints[i] = null;

    r.gc(); // request garbage collection

    mem2 = r.freeMemory();
    System.out.println("Free memory after collecting" +
                       " discarded Integers: " + mem2);

  }
}

Output of Above Java Program
Total memory is: 16121856
Initial free memory: 15837912
Free memory after garbage collection: 16123344
Free memory after allocation: 16031528
Memory used by allocation: 91816
Free memory after collecting discarded Integers: 16123344

[ Read More ]

Convert an integer into binary, hexadecimal, and octal.

Here is a Java Program to Convert an integer into binary, hexadecimal, and octal.

class StringConversions {
  public static void main(String args[]) {
    int num = 19648;

    System.out.println(num + " in binary: " +
                       Integer.toBinaryString(num));

    System.out.println(num + " in octal: " +
                       Integer.toOctalString(num));

    System.out.println(num + " in hexadecimal: " +
                       Integer.toHexString(num));
  }
}

Output of Above Java Program
19648 in binary: 100110011000000
19648 in octal: 46300
19648 in hexadecimal: 4cc0

[ Read More ]

Program to sum the Inputted Number with Previous Sum

This program sums a list of numbers entered by the user. It converts the string representation of each number into an int using parseInt().

import java.io.*;

class ParseDemo {
  public static void main(String args[]) 
    throws IOException
  {
    // create a BufferedReader using System.in
    BufferedReader br = new
      BufferedReader(new InputStreamReader(System.in));
    String str;
    int i;
    int sum=0;
    
    System.out.println("Enter numbers, 0 to quit.");
    do {
      str = br.readLine();
      try {
        i = Integer.parseInt(str);
      } catch(NumberFormatException e) {
        System.out.println("Invalid format");
        i = 0;
      }
      sum += i;
      System.out.println("Current sum is: " + sum);
    } while(i != 0);
  }
}

Output of Above Java Program
Enter numbers, 0 to quit.
1
Current sum is: 1
2
Current sum is: 3
4
Current sum is: 7
5
Current sum is: 12
8
Current sum is: 20
0
Current sum is: 20

[ Read More ]

Using trim() to process commands.

Here is a Java Program for Using trim() to process commands.

import java.io.*;

class UseTrim {
  public static void main(String args[]) 
    throws IOException
  {
    // create a BufferedReader using System.in
    BufferedReader br = new
      BufferedReader(new InputStreamReader(System.in));
    String str;

    System.out.println("Enter 'stop' to quit.");
    System.out.println("Enter State: ");
    do {
      str = br.readLine();
      str = str.trim(); // remove whitespace

      if(str.equals("Illinois"))
        System.out.println("Capital is Springfield.");
      else if(str.equals("Missouri"))
        System.out.println("Capital is Jefferson City.");
      else if(str.equals("California"))
        System.out.println("Capital is Sacramento.");
      else if(str.equals("Washington"))
        System.out.println("Capital is Olympia.");
      // ... 
    } while(!str.equals("stop"));
  }
}

Output of Above Java Program
Enter 'stop' to quit.
Enter State:
California
Capital is Sacramento.
stop

[ Read More ]

To Substitute the Substring from given String

Here is a Java Program for Substring replacement

class StringReplace {
  public static void main(String args[]) {
    String org = "This is a test. This is, too.";
    String search = "is";
    String sub = "was";
    String result = "";
    int i;

    do { // replace all matching substrings
      System.out.println(org);
      i = org.indexOf(search);
      if(i != -1) {
        result = org.substring(0, i);
        result = result + sub;
        result = result + org.substring(i + search.length());
        org = result;
      }
    } while(i != -1);

  }
}

Output of Above Java Program
This is a test. This is, too.
Thwas is a test. This is, too.
Thwas was a test. This is, too.
Thwas was a test. Thwas is, too.
Thwas was a test. Thwas was, too.

[ Read More ]

To Demonstrate indexOf() and lastIndexOf().

Here is a Java Program to Demonstrate indexOf() and lastIndexOf().

class indexOfDemo {
  public static void main(String args[]) {
    String s = "Now is the time for all good men " +
               "to come to the aid of their country.";

    System.out.println(s);
    System.out.println("indexOf(t) = " +
                       s.indexOf('t'));
    System.out.println("lastIndexOf(t) = " +
                       s.lastIndexOf('t'));
    System.out.println("indexOf(the) = " +
                       s.indexOf("the"));
    System.out.println("lastIndexOf(the) = " +
                       s.lastIndexOf("the"));
    System.out.println("indexOf(t, 10) = " +
                       s.indexOf('t', 10));
    System.out.println("lastIndexOf(t, 60) = " +
                       s.lastIndexOf('t', 60));
    System.out.println("indexOf(the, 10) = " +
                       s.indexOf("the", 10));
    System.out.println("lastIndexOf(the, 60) = " +
                       s.lastIndexOf("the", 60));
  }
}

Output of Above Java Program
Now is the time for all good men to come to the aid of their country.
indexOf(t) = 7
lastIndexOf(t) = 65
indexOf(the) = 7
lastIndexOf(the) = 55
indexOf(t, 10) = 11
lastIndexOf(t, 60) = 55
indexOf(the, 10) = 44
lastIndexOf(the, 60) = 55

[ Read More ]

To Apply Bubble Sort on Strings

Here is a Java Program to Bubble Sort for Strings

class SortString {
  static String arr[] = {
    "Now", "is", "the", "time", "for", "all", "good", "men",
    "to", "come", "to", "the", "aid", "of", "their", "country"
  };
  public static void main(String args[]) {
    for(int j = 0; j < arr.length; j++) {
      for(int i = j + 1; i < arr.length; i++) {
        if(arr[i].compareTo(arr[j]) < 0) {
          String t = arr[j];
          arr[j] = arr[i];
          arr[i] = t;
        }
      }
      System.out.println(arr[j]);
    }
  }
}

Output of Above Java Program
Now
aid
all
come
country
for
good
is
men
of
the
the
their
time
to
to

[ Read More ]

To Demonstrate instanceof operator

Here is a Java Program to Demonstrate instanceof operator

class A {
  int i, j;
}

class B {
  int i, j;
}

class C extends A {
  int k;
}

class D extends A {
  int k;
}

class InstanceOf {
  public static void main(String args[]) {
    A a = new A();
    B b = new B();
    C c = new C();
    D d = new D();

    if(a instanceof A) 
      System.out.println("a is instance of A");
    if(b instanceof B) 
      System.out.println("b is instance of B");
    if(c instanceof C) 
      System.out.println("c is instance of C");
    if(c instanceof A) 
      System.out.println("c can be cast to A");

    if(a instanceof C) 
      System.out.println("a can be cast to C");

    System.out.println();

    // compare types of derived types
    A ob;

    ob = d; // A reference to d
    System.out.println("ob now refers to d");
    if(ob instanceof D) 
      System.out.println("ob is instance of D");

    System.out.println();

    ob = c; // A reference to c
    System.out.println("ob now refers to c");

    if(ob instanceof D) 
      System.out.println("ob can be cast to D");
    else
      System.out.println("ob cannot be cast to D");

    if(ob instanceof A) 
      System.out.println("ob can be cast to A");

    System.out.println();

    // all objects can be cast to Object
    if(a instanceof Object) 
      System.out.println("a may be cast to Object");
    if(b instanceof Object) 
      System.out.println("b may be cast to Object");
    if(c instanceof Object) 
      System.out.println("c may be cast to Object");
    if(d instanceof Object) 
      System.out.println("d may be cast to Object");
  }
}

Output of Above Java Program
a is instance of A
b is instance of B
c is instance of C
c can be cast to A

ob now refers to d
ob is instance of D

ob now refers to c
ob cannot be cast to D
ob can be cast to A

a may be cast to Object
b may be cast to Object
c may be cast to Object
d may be cast to Object

[ Read More ]

Java Program to Copy a text file

Here is a Java Program to Copy a text file.

To use this program, specify the name  of the source file and the destination file. For example, to copy a file called FIRST.TXT to a file called SECOND.TXT, use the following command line. 
java CopyFile FIRST.TXT SECOND.TXT

import java.io.*;

class CopyFile {
  public static void main(String args[]) 
    throws IOException
  {
    int i;
    FileInputStream fin;
    FileOutputStream fout;

    try {
      // open input file
      try {
        fin = new FileInputStream(args[0]);
      } catch(FileNotFoundException e) {
        System.out.println("Input File Not Found");
        return;
      }

      // open output file
      try {
        fout = new FileOutputStream(args[1]);
      } catch(FileNotFoundException e) {
        System.out.println("Error Opening Output File");
        return;
      }
    } catch(ArrayIndexOutOfBoundsException e) {
      System.out.println("Usage: CopyFile From To");
      return;
    }

    // Copy File
    try {
      do {
        i = fin.read();
        if(i != -1) fout.write(i);
      } while(i != -1);
    } catch(IOException e) {
      System.out.println("File Error");
    }

    fin.close();
    fout.close();
  }
}

[ Read More ]

To Display a Text File Using Java IO

Here is a Java Program to Display a text file.

To use this program, specify the name  of the file that you want to see. For example, to see a file called TEST.TXT, use the following command line.
java ShowFile TEST.TXT

import java.io.*;

class ShowFile {
  public static void main(String args[]) 
    throws IOException
  {
    int i;
    FileInputStream fin;

    try {
      fin = new FileInputStream(args[0]);
    } catch(FileNotFoundException e) {
      System.out.println("File Not Found");
      return;
    } catch(ArrayIndexOutOfBoundsException e) {
      System.out.println("Usage: ShowFile File");
      return;
    }

    // read characters until EOF is encountered
    do {
      i = fin.read();
      if(i != -1) System.out.print((char) i);
    } while(i != -1);

    fin.close();
  }
}

[ Read More ]

Read String from Using the BufferedReader

Here is a Java Program to Read String from Using the BufferedReader

import java.io.*;

class BRReadLines {
  public static void main(String args[]) 
    throws IOException
  {
    // create a BufferedReader using System.in
    BufferedReader br = new BufferedReader(new 
                            InputStreamReader(System.in));
    String str;

    System.out.println("Enter lines of text.");
    System.out.println("Enter 'stop' to quit.");
    do {
      str = br.readLine();
      System.out.println(str);
    } while(!str.equals("stop"));
  }
}

Output of Above Java Program
Enter lines of text.
Enter 'stop' to quit.
Java Programming Language Tutorial
Java Programming Language Tutorial
stop
stop

[ Read More ]

Read Character from Console using BufferedReader

Here is a Java Program to Read Character from the Console using BufferedReader

import java.io.*;

class BRRead {
  public static void main(String args[]) 
    throws IOException
  {
    char c;
    BufferedReader br = new
    BufferedReader(new InputStreamReader(System.in));
    System.out.println("Enter characters, 'q' to quit.");

    // read characters
    do {
      c = (char) br.read();
      System.out.println(c);
    } while(c != 'q');
  }
}

Output of Above Java Program
Java Programming Language Tutorial
J
a
v
a

P
r
o
g
r
a
m
m
i
n
g

L
a
n
g
u
a
g
e

T
u
t
o
r
i
a
l


q
q

[ Read More ]

Suspending and Resuming a Thread

Here is a Java Program to Suspending and resuming a thread

class NewThread implements Runnable {
  String name; // name of thread
  Thread t;
  boolean suspendFlag;
  
  NewThread(String threadname) {
    name = threadname;
    t = new Thread(this, name);
    System.out.println("New thread: " + t);
    suspendFlag = false;
    t.start(); // Start the thread
  }

  // This is the entry point for thread.
  public void run() {
    try {
      for(int i = 15; i > 0; i--) {
        System.out.println(name + ": " + i);
        Thread.sleep(200);
        synchronized(this) {
          while(suspendFlag) {
            wait();
          }
        }
      }
    } catch (InterruptedException e) {
      System.out.println(name + " interrupted.");
    }
    System.out.println(name + " exiting.");
  }

  void mysuspend() {
    suspendFlag = true;
  }

  synchronized void myresume() {
    suspendFlag = false;
    notify();
  }
}

class SuspendResume {
  public static void main(String args[]) {
    NewThread ob1 = new NewThread("One");
    NewThread ob2 = new NewThread("Two");

    try {
      Thread.sleep(1000);
      ob1.mysuspend();
      System.out.println("Suspending thread One");
      Thread.sleep(1000);
      ob1.myresume();
      System.out.println("Resuming thread One");
      ob2.mysuspend();
      System.out.println("Suspending thread Two");
      Thread.sleep(1000);
      ob2.myresume();
      System.out.println("Resuming thread Two");
    } catch (InterruptedException e) {
      System.out.println("Main thread Interrupted");
    }

    // wait for threads to finish
    try {
      System.out.println("Waiting for threads to finish.");
      ob1.t.join();
      ob2.t.join();
    } catch (InterruptedException e) {
      System.out.println("Main thread Interrupted");
    }
 
    System.out.println("Main thread exiting.");
  }
}

Output of Above Java Program
New thread: Thread[One,5,main]
New thread: Thread[Two,5,main]
One: 15
Two: 15
Two: 14
One: 14
One: 13
Two: 13
Two: 12
One: 12
One: 11
Two: 11
One: 10
Two: 10
Suspending thread One
Two: 9
Two: 8
Two: 7
Two: 6
Resuming thread One
One: 9
Suspending thread Two
One: 8
One: 7
One: 6
One: 5
Two: 5
Resuming thread Two
One: 4
Waiting for threads to finish.
Two: 4
One: 3
One: 2
Two: 3
One: 1
Two: 2
Two: 1
One exiting.
Two exiting.
Main thread exiting.

[ Read More ]

Applying MultiThreading using Synchronization

Here is a Java Program to Applying MultiThreading using Synchronization.

class Callme {
  void call(String msg) {
    System.out.print("[" + msg);
    try {
      Thread.sleep(1000);
    } catch (InterruptedException e) {
      System.out.println("Interrupted");
    }
    System.out.println("]");
  }
}

class Caller implements Runnable {
  String msg;
  Callme target;
  Thread t;

  public Caller(Callme targ, String s) {
    target = targ;
    msg = s;
    t = new Thread(this);
    t.start();
  }

  // synchronize calls to call()
  public void run() {
    synchronized(target) { // synchronized block
      target.call(msg);
    }
  }
}

class Synch1 {
  public static void main(String args[]) {
    Callme target = new Callme();
    Caller ob1 = new Caller(target, "Hello");
    Caller ob2 = new Caller(target, "Synchronized");
    Caller ob3 = new Caller(target, "World");

    // wait for threads to end
    try {
      ob1.t.join();
      ob2.t.join();
      ob3.t.join();
    } catch(InterruptedException e) {
      System.out.println("Interrupted");
    }
  }
}

Output of Above Java Program
[Hello]
[Synchronized]
[World]

[ Read More ]

Demonstrating Thread Priorities by Changing their Priority

Here is a Java Program to Demonstrating Thread Priorities.

class clicker implements Runnable {
  int click = 0;
  Thread t;
  private volatile boolean running = true;

  public clicker(int p) {
    t = new Thread(this);
    t.setPriority(p);
  }

  public void run() {
    while (running) {
      click++;
    }
  }

  public void stop() {
    running = false;
  }

  public void start() {
    t.start();
  }
}

class HiLoPri {
  public static void main(String args[]) {
    Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
    clicker hi = new clicker(Thread.NORM_PRIORITY + 2);
    clicker lo = new clicker(Thread.NORM_PRIORITY - 2);

    lo.start();
    hi.start();
    try {
      Thread.sleep(10000);
    } catch (InterruptedException e) {
        System.out.println("Main thread interrupted.");
    }

    lo.stop();
    hi.stop();

    // Wait for child threads to terminate.
    try {
      hi.t.join();
      lo.t.join();
    } catch (InterruptedException e) {
      System.out.println("InterruptedException caught");
    }

    System.out.println("Low-priority thread: " + lo.click); 
    System.out.println("High-priority thread: " + hi.click);
  }
}

Output of Above Java Program
Low-priority thread: -992923544
High-priority thread: -320333802

[ Read More ]

Create multiple threads by Implementing Runnable Interface

Here is a Java Program to Create multiple threads

class NewThread implements Runnable {
  String name; // name of thread
  Thread t;

  NewThread(String threadname) {
    name = threadname;
    t = new Thread(this, name);
    System.out.println("New thread: " + t);
    t.start(); // Start the thread
  }

  // This is the entry point for thread.
  public void run() {
    try {
      for(int i = 5; i > 0; i--) {
        System.out.println(name + ": " + i);
        Thread.sleep(1000);
      }
    } catch (InterruptedException e) {
      System.out.println(name + "Interrupted");
    }
    System.out.println(name + " exiting.");
  }
}

class MultiThreadDemo {
  public static void main(String args[]) {
    new NewThread("One"); // start threads
    new NewThread("Two");
    new NewThread("Three");

    try {
      // wait for other threads to end
      Thread.sleep(10000);
    } catch (InterruptedException e) {
      System.out.println("Main thread Interrupted");
    }

    System.out.println("Main thread exiting.");
  }
}

Output of Above Java Program
New thread: Thread[One,5,main]
New thread: Thread[Two,5,main]
One: 5
New thread: Thread[Three,5,main]
Two: 5
Three: 5
One: 4
Two: 4
Three: 4
One: 3
Two: 3
Three: 3
One: 2
Three: 2
Two: 2
One: 1
Three: 1
Two: 1
One exiting.
Two exiting.
Three exiting.
Main thread exiting.

[ Read More ]

Demonstrate MultiThreading by Extending Thread Class

Here is a Java Program to Demonstrate the MultiThreading by Extending Thread Class

class NewThread extends Thread {

  NewThread() {
    super("Demo Thread");
    System.out.println("Child thread: " + this);
    start(); // Start the thread
  }

  public void run() {
    try {
      for(int i = 5; i > 0; i--) {
        System.out.println("Child Thread: " + i);
        Thread.sleep(500);
      }
    } catch (InterruptedException e) {
      System.out.println("Child interrupted.");
    }
    System.out.println("Exiting child thread.");
  }
}

class ExtendThread {
  public static void main(String args[]) {
    new NewThread(); // create a new thread

    try {
      for(int i = 5; i > 0; i--) {
        System.out.println("Main Thread: " + i);
        Thread.sleep(1000);
      }
    } catch (InterruptedException e) {
      System.out.println("Main thread interrupted.");
    }
    System.out.println("Main thread exiting.");
  }
}

Output of Above Java Program
Current thread: Thread[main,5,main]
After name change: Thread[My Thread,5,main]
5
4
3
2
1

[ Read More ]

Create a Custom Exception Type

Here is a Java Program to creates a custom exception type.

class MyException extends Exception {
  private int detail;

  MyException(int a) {
    detail = a;
  }

  public String toString() {
    return "MyException[" + detail + "]";
  }
}

class ExceptionDemo {
  static void compute(int a) throws MyException {
    System.out.println("Called compute(" + a + ")");
    if(a > 10)
      throw new MyException(a);
    System.out.println("Normal exit");
  }

  public static void main(String args[]) {
    try {
      compute(1);
      compute(20);
    } catch (MyException e) {
      System.out.println("Caught " + e);
    }
  }
}

Output of Above Java Program
Called compute(1)
Normal exit
Called compute(20)
Caught MyException[20]

[ Read More ]

Finally Executed after Calling the Function

Here is a Java Program to Demonstrate the Finally Block

class FinallyDemo {
  // Through an exception out of the method.
  static void procA() {
    try {
      System.out.println("inside procA");
      throw new RuntimeException("demo");
    } finally {
      System.out.println("procA's finally");
    }
  }

  // Return from within a try block.
  static void procB() {
    try {
      System.out.println("inside procB");
      return;
    } finally {
      System.out.println("procB's finally");
    }
  }

  // Execute a try block normally.
  static void procC() {
    try {
      System.out.println("inside procC");
    } finally {
      System.out.println("procC's finally");
    }
  }

  public static void main(String args[]) {
    try {
      procA();
    } catch (Exception e) {
      System.out.println("Exception caught");
    }
    procB();
    procC();
  }
}

Output of Above Java Program
inside procA
procA's finally
Exception caught
inside procB
procB's finally
inside procC
procC's finally

[ Read More ]

Nested Try to Handle Divided by Zero Error

Here is a Java Program to Demonstrate the Nested Try

class MethNestTry {
  static void nesttry(int a) {
    try { // nested try block
      /* If one command line arg is used,
         then an divide-by-zero exception 
         will be generated by the following code. */
      if(a==1) a = a/(a-a); // division by zero

      /* If two command line args are used
         then generate an out-of-bounds exception. */     
      if(a==2) {
        int c[] = { 1 };
        c[42] = 99; // generate an out-of-bounds exception
      }
    } catch(ArrayIndexOutOfBoundsException e) {
      System.out.println("Array index out-of-bounds: " + e);
    }
  }

  public static void main(String args[]) {
    try {
      int a = args.length;

      /* If no command line args are present,
         the following statement will generate
         a divide-by-zero exception. */
      int b = 42 / a;

      System.out.println("a = " + a);

      nesttry(a);
    } catch(ArithmeticException e) {
      System.out.println("Divide by 0: " + e);
    }
  }
}

Output of Above Java Program
Divide by 0: java.lang.ArithmeticException: / by zero

[ Read More ]

Make BullsEye Target Using Java AWT and Swing Classes

Here is a Java Program to Make BullsEye Target Using Java AWT and Swing Classes

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

class BullseyeDemo {
 
    public static void main(String[] args) {
        JFrame target = new BullseyeWindow();
        target.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        target.setVisible(true);
    }
}

class BullseyeWindow extends JFrame {
    int initialRings = 10; // Number of rings to start with.
    Bullseye be;           // The panel that draws the bullseye

    public BullseyeWindow() {
        JSlider slide = new JSlider(JSlider.HORIZONTAL, 0, 30, initialRings);
        slide.setMajorTickSpacing(5); // sets numbers for biggest tick marks
        slide.setPaintLabels(true);   // display numbers on major ticks
        slide.setMinorTickSpacing(1); // smaller tick marks
        slide.setPaintTicks(true);    // display the ticks
        slide.addChangeListener(new ChangeListener() {
                public void stateChanged(ChangeEvent e) {
                    int num = ((JSlider)(e.getSource())).getValue();
                    be.setRings(num);
                }
            });

        be = new Bullseye();
        be.setRings(initialRings);

        Container content = this.getContentPane();
        content.setLayout(new BoxLayout(content, BoxLayout.Y_AXIS));
        content.add(slide);
        content.add(be);
        
        this.setTitle("BullseyeDemo");
        this.pack();
        this.setResizable(false);
    }
}


class Bullseye extends JPanel {
    static final int SIZE = 300; // initial window size
    int rings = 5;  // Number of rings to draw in bullseye

    public Bullseye() {
        this.setBackground(Color.white);
        this.setPreferredSize(new Dimension(SIZE, SIZE));
    }
    
    public void setRings(int r) {
        rings = r;
        this.repaint();  // new value of rings - better repaint
    }
    
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        int x = SIZE/2;  // x,y of top left corner for drawing circles
        int y = SIZE/2;
        
        for (int i=rings; i>0; i--) {
            if (i%2 == 0) {
                g.setColor(Color.red);
            } else {
                g.setColor(Color.blue);
            }
            int radius = i * 100/rings;  // compute radius of this ring
            g.fillOval(x-radius, y-radius, radius*2, radius*2);
        }
    }
}

Output of Above Java Program

On Running The Program

When Move Slider to 24

[ Read More ]

Make a Sleepy Face Using a Java AWT Class

Here is a Java Program to Make a Sleepy Face Using a AWT Class

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;


/***********class Sleepy*******************/
class Sleepy {

    public static void main(String[] args) {
        JFrame windo = new JFrame("Sleepy");
        windo.getContentPane().add(new SleepyPanel());
        windo.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        windo.pack();
        windo.show();
    }
}


class SleepyPanel extends JPanel {
    private Sleeper face = new Sleeper();

    SleepyPanel() {
        JButton awakeButton = new JButton("Awake");
        awakeButton.addActionListener(
            new ActionListener() {

                public void actionPerformed(ActionEvent e) {
                    face.setAwake(true);
                }
            }
        );
        JButton asleepButton = new JButton("Asleep");
        asleepButton.addActionListener(
            new ActionListener() {

                public void actionPerformed(ActionEvent e) {
                    face.setAwake(false);
                }
            }
        );

        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new FlowLayout());
        buttonPanel.add(awakeButton);
        buttonPanel.add(asleepButton);

        this.setLayout(new BorderLayout());
        this.add(buttonPanel, BorderLayout.NORTH);
        this.add(face, BorderLayout.CENTER);
    }
}

class Sleeper extends JPanel {

    private boolean awake = false;  // show face awake or asleep

    Sleeper() {
        this.setBackground(Color.lightGray);
        this.setPreferredSize(new Dimension(400, 400));  // size
    }

    public void setAwake(boolean awakeAsleep) {
        awake = awakeAsleep; // remember expression on face
        repaint();           // redraw it with new value
    }


    public void paintComponent(Graphics g) {
        super.paintComponent(g);  // MUST be first line

        //--- draw head
        g.setColor(Color.yellow);
        g.fillOval(8, 8, 384, 384);

        //--- draw eyes
        g.setColor(Color.black);
        if (awake) {
            g.fillOval(100, 150, 50, 100);  // left eye
            g.fillOval(250, 150, 50, 100);  // right eye
        }
        else {
            g.fillRect(50 , 200, 100, 4); // left eye
            g.fillRect(250, 200, 100, 4); // left eye
        }
    }
}

Output of Above Java Program

When Clicked on Awake Button

When Clicked on Asleep Button

[ Read More ]

Find the Body Mass Index Using AWT and Swing Classes

Here is a Java Program to Find the Body Mass Index Using AWT and Swing Classes

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

class BMI extends JFrame {
    public static void main(String[] args) {
        BMI window = new BMI();
        window.setVisible(true);
    }


    private JTextField _mField   = new JTextField(4);  // height
    private JTextField _kgField  = new JTextField(4);  // weight
    private JTextField _bmiField = new JTextField(4);  // BMI

    /****************constructor********************/
    public BMI() {
        //Create button and add action listener.
        JButton bmiButton = new JButton("Compute BMI");
        bmiButton.addActionListener(new BMIListener());

        //Set layout and add components.
        JPanel content = new JPanel();
        content.setLayout(new FlowLayout());
        content.add(new JLabel("Weight in kilograms"));
        content.add(_kgField);
        content.add(new JLabel("Height in meters"));
        content.add(_mField);
        content.add(bmiButton);
        content.add(new JLabel("Your BMI is"));
        content.add(_bmiField);

        //Set the window characteristics.
        setContentPane(content);
        setTitle("Body Mass Index");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pack();                          // Do layout.
        setLocationRelativeTo(null);     // Center window.
    }

    /******************* inner class BMIListener *********************/
    // Inner class is used to access components.
    // BMI is converted to int to eliminate excess "accuracy".
    private class BMIListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            double kilograms = Double.parseDouble(_kgField.getText());
            double meters    = Double.parseDouble(_mField.getText());
            int    bmi       = (int)computeBMI(kilograms, meters);
            _bmiField.setText("" + bmi);
        }
    }

    //logic method computeBMI
    public static double computeBMI(double weight, double height) {
        return weight / (height * height);
    }
}

Output of Above Java Program

[ Read More ]

To Find the Extension of Given File Using JOptionPane Dialog Box

Here is a Java Program to Find the Extension of Given File Using JOptionPane Dialog Box

import javax.swing.*;

class FileExt {

    public static void main(String[] args) {
        //... Declare local variables.
        String fileName;   // The file name the user entered.
        String extension;  // The extension.

        //... Input a file name and remove whitespace.
        fileName = JOptionPane.showInputDialog(null, "Enter file name.");
        fileName = fileName.trim();

        //... Find the position of the last dot.  Get extension.
        int dotPos = fileName.lastIndexOf(".");
        extension = fileName.substring(dotPos);

        //... Output extension.
        JOptionPane.showMessageDialog(null, "Extension is " + extension);
    }
}

Output of Above Java Program

[ Read More ]

Java String Program to buffer Strings

Here is a Java Program to buffer strings

class StringBuffer{
   public static void main(String[] args) {
      countTo_N_Improved();
   }
   private final static int MAX_LENGTH=30;
   private static String buffer = "";
   private static void emit(String nextChunk) {
      if(buffer.length() + nextChunk.length() > MAX_LENGTH) {
         System.out.println(buffer);
         buffer = "";  
      }
      buffer += nextChunk;
   }
   private static final int N=100;
   private static void countTo_N_Improved() {
      for (int count=2; count<=N; count=count+2) {
         emit(" " + count);
      }
   }
}

Output of Above Java Program

 2 4 6 8 10 12 14 16 18 20 22
 24 26 28 30 32 34 36 38 40 42
 44 46 48 50 52 54 56 58 60 62
 64 66 68 70 72 74 76 78 80 82

[ Read More ]

To Determine the Unicode Code Point in String

Here is a Java Program to determine the Unicode code point in string

class StringUniCode{
   public static void main(String[] args){
      String test_string="Welcome to JavaProgramming";
      System.out.println("String under test is = "+test_string);
      System.out.println("Unicode code point at" 
      +" position 5 in the string is = "
      +  test_string.codePointBefore(5));
   }
}

Output of Above Java Program
String under test is = Welcome to JavaProgramming
Unicode code point at position 5 in the string is = 111

[ Read More ]

To Compare Performance of String Creation

Here is a Java Program to compare performance of string creation

class StringComparePerformance{
   public static void main(String[] args){      
      long startTime = System.currentTimeMillis();
      for(int i=0;i<50000;i++){
         String s1 = "hello";
         String s2 = "hello"; 
      }
      long endTime = System.currentTimeMillis();
      System.out.println("Time taken for creation" 
      + " of String literals : "+ (endTime - startTime) 
      + " milli seconds" );       
      long startTime1 = System.currentTimeMillis();
      for(int i=0;i<50000;i++){
         String s3 = new String("hello");
         String s4 = new String("hello");
      }
      long endTime1 = System.currentTimeMillis();
      System.out.println("Time taken for creation" 
      + " of String objects : " + (endTime1 - startTime1)
      + " milli seconds");
   }
}

Output of Above Java Program
Time taken for creation of String literals : 2 milli seconds
Time taken for creation of String objects : 5 milli seconds

[ Read More ]

To Replace a Substring inside a String by Another One

Here is a Java Program to replace a substring inside a string by another one

public class StringReplaceEmp{
   public static void main(String args[]){
      String str="Hello World";
      System.out.println( str.replace( 'H','W' ) );
      System.out.println( str.replaceFirst("He", "Wa") );
      System.out.println( str.replaceAll("He", "Ha") );
   }
}

Output of Above Java Program
Wello World
Wallo World
Hallo World

[ Read More ]

To Remove a Particular Character From a String

Here is a Java Program to remove a particular character from a string

class Main {
   public static void main(String args[]) {
      String str = "this is Java";
      System.out.println(removeCharAt(str, 3));
   }
   public static String removeCharAt(String s, int pos) {
      return s.substring(0, pos) + s.substring(pos + 1);
   }
}

Output of Above Java Program
thi is Java

[ Read More ]

To Search the Last Position of a Substring

Here is a Java Program to search the last position of a substring

class SearchlastString {
   public static void main(String[] args) {
      String strOrig = "Hello world ,Hello Reader";
      int lastIndex = strOrig.lastIndexOf("Hello");
      if(lastIndex == - 1){
         System.out.println("Hello not found");
      }else{
         System.out.println("Last occurrence of Hello is at index "+ lastIndex);
      }
   }
}

Output of Above Java Program
Last occurrence of Hello is at index 13

[ Read More ]

To Search the Last Position of a Substring

Here is a Java Program to search the last position of a substring

class SearchlastString {
   public static void main(String[] args) {
      String strOrig = "Hello world ,Hello Reader";
      int lastIndex = strOrig.lastIndexOf("Hello");
      if(lastIndex == - 1){
         System.out.println("Hello not found");
      }else{
         System.out.println("Last occurrence of Hello is at index "+ lastIndex);
      }
   }
}

Output of Above Java Program
Last occurrence of Hello is at index 13

[ Read More ]

Insert all elements of other Collection to Specified Index of Java ArrayList

Here is a Java Program to Insert all elements of other Collection to Specified Index of Java ArrayList Example

import java.util.ArrayList;
import java.util.Vector;
 
class ArrayListExample { 
  public static void main(String[] args) {
    ArrayList arrayList = new ArrayList();
   
    arrayList.add("1");
    arrayList.add("2");
    arrayList.add("3");

    Vector v = new Vector();
    v.add("4");
    v.add("5");
   
    arrayList.addAll(1,v);
   
    System.out.println("After inserting all elements of Vector at index 1, ArrayList Content: ");
    for(int i=0; i<arrayList.size(); i++)
      System.out.println(arrayList.get(i)); 
  }
}

Output of Above Java Program
After inserting all elements of Vector at index 1, ArrayList contains..
1
4
5
2
3

[ Read More ]

Get Sub List of Java ArrayList Example

Here is a Java Program to Get Sub List of Java ArrayList Example

import java.util.ArrayList;
import java.util.List;
 
class ArrayListExample { 
  public static void main(String[] args) {
   
    ArrayList arrayList = new ArrayList();

    arrayList.add("1");
    arrayList.add("2");
    arrayList.add("3");
    arrayList.add("4");
    arrayList.add("5");
   
    List lst = arrayList.subList(1,3);

    System.out.println("Sub List contains : ");
    for(int i=0; i< lst.size() ; i++)
      System.out.println(lst.get(i));
     
    Object obj = lst.remove(0);
    System.out.println(obj + " is removed from sub list");

    System.out.println("After removing " + obj + " from sub list, original ArrayList Contains : ");
    for(int i=0; i< arrayList.size() ; i++)
      System.out.println(arrayList.get(i));   
  }
}

Output of Above Java Program
Sub list contains :
2
3
2 is removed from sub list
After removing 2 from sub list, original ArrayList contains :
1
3
4
5

[ Read More ]

Get Size of Java ArrayList and Loop through Elements

Here is a Java Program to Get Size of Java ArrayList and loop through elements Example

import java.util.ArrayList;
 
class ArrayListExample { 
  public static void main(String[] args) {
   
    ArrayList arrayList = new ArrayList();
   
    arrayList.add("1");
    arrayList.add("2");
    arrayList.add("3");
 
    int totalElements = arrayList.size();
   
    System.out.println("ArrayList Content : ");

    for(int index=0; index < totalElements; index++)
      System.out.println(arrayList.get(index));
  }
}

Output of Above Java Program
ArrayList Content :
1
2
3

[ Read More ]

List which contains the Argument from the Command Line

Here is a Java Program to Output the List which contains the Argument from the Command Line

import java.util.*;

class Shuffle {
 public static void main(String[] args){
         List<String> list = new ArrayList<String>();
         
  for (String a : args)
              list.add(a);
      
  Collections.shuffle(list, new Random());
         System.out.println(list);
     }
}

Output of Above Java Program
When This Programs is Executed through the Command Line with Argument as Follows

C:>Java Programs>Java Shuffle Java Programming Language Tutorial

It will Result the Following Output:

[Java,Programming,Language,Tutorial]

[ Read More ]

Copy all elements of Java ArrayList to an Object Array Example

Here is a Java Program to Copy all elements of Java ArrayList to an Object Array Example

import java.util.ArrayList;
 
class CopyElementsOfArrayListToArrayExample {
 
  public static void main(String[] args) {
    ArrayList arrayList = new ArrayList();
   
    arrayList.add("1");
    arrayList.add("2");
    arrayList.add("3");
    arrayList.add("4");
    arrayList.add("5");
   
    Object[] objArray = arrayList.toArray();
   
    System.out.println("ArrayList elements are copied into an Array. Now Array Contains..");
    for(int index=0; index < objArray.length ; index++)
      System.out.println(objArray[index]);
  }
}

Output of Above Java Program
ArrayList elements are copied into an Array. Now Array Contains..
1
2
3
4
5

[ Read More ]

Append all elements of other Collection to Java ArrayList

Here is a Java Program to Append all elements of other Collection to Java ArrayList Example

import java.util.ArrayList;
import java.util.Vector;
 
class ArrayListExample {
 
  public static void main(String[] args) {
 
    ArrayList arrayList = new ArrayList();

    arrayList.add("1");
    arrayList.add("2");
    arrayList.add("3");
   
    Vector v = new Vector();
    v.add("4");
    v.add("5");

    arrayList.addAll(v);

    System.out.println("After appending all elements of Vector, ArrayList contains..");
    for(int i=0; i<arrayList.size(); i++)
      System.out.println(arrayList.get(i)); 
  }
}

Output of Above Java Program
After appending all elements of Vector, ArrayList contains..
1
2
3
4
5

[ Read More ]

Add an element to specified index of Java ArrayList

Here is a Java Program to Add an element to specified index of Java ArrayList Example

import java.util.ArrayList;

class AddElementToSpecifiedIndexArrayListExample { 
  public static void main(String[] args) {
   
    ArrayList arrayList = new ArrayList();
    
    arrayList.add("1");
    arrayList.add("2");
    arrayList.add("3");
   
    
    arrayList.add(1,"INSERTED ELEMENT");
   
    
    System.out.println("ArrayList Contents : ");
    
    for(int index=0; index < arrayList.size(); index++)
      System.out.println(arrayList.get(index));
   
  }
}

Output of Above Java Program
ArrayList Contents :
1
INSERTED ELEMENT
2
3

[ Read More ]

To Calculate the Power and Square Root of a Given Number

Here is a Java Program to Calculate the Power and  Square Root of a Given Number

import java.util.Scanner;

class power_sqrt {
 public static void main(String a[]){
    int power;
    float base;
        
  Scanner sc=new Scanner(System.in);  
  
  System.out.println("Enter the value of exponent");
  power=sc.nextInt();
  System.out.println("Enter the value for base");
  base=sc.nextFloat();
  number pow=new number();
  number sqr=new number();
  System.out.println("the value for power fun:-> "+pow.power(base, power));
  System.out.println("the value for square this is sqr of base:-> "+sqr.squre(base));
 } 
}

class number{
 float base;
 int expo;
 float power(float a,int b){
  if(b==1)
   return a;
  if(b==0)
   return 1;  
  else
   return(a*power(a,b-1));  
 }
 
 float squre(float base){  
  return base*base;  
 }
}

Output of Above Java Program
Enter the value of exponent
5
Enter the value for base
8
the value for power fun:-> 32768.0
the value for square this is sqr of base:-> 64.0

[ Read More ]

To Demonstrate the Simple Array Iterator

Here is a Java Program to Demonstrate the Simple Array Iterator.

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Iterator that works over an array of Objects
 * Use it: Iterator iter = new ArrayIterator( myArray );
 *
 */
class SimpleArrayIterator implements Iterator{

   /**
    * True if we are debugging, includes main
    * test driver code.
    */
   static final boolean debugging = true;

   /**
    * Reference to the original array we will
    * iterate over. Not a copy of the array.
    */
   Object[] array;

   /**
    * How far down the array we have iterated so far.
    */
   int pos;

   /**
    * public constructor
    *
    * @param a The array we are to iterate over. It must
    * be an array of Objects of some sort not
    * int[] etc.
    */
 public SimpleArrayIterator( Object[] a ){
  array = a;
  pos = 0;
    }

   /**
    * Is there yet another element in the array
    * to go?
    *
    * @return true if there are more elements
    */
 public boolean hasNext(){
  return( pos < array.length );
    }

   /**
    * Get the next element of the array.
    *
    * @return Next element of a the array. You must cast
    * it back to its proper type from Object.
    * @exception NoSuchElementException
    */
   public Object next() throws NoSuchElementException{
      if ( pos >= array.length )
         throw new NoSuchElementException();

      return array[pos++];
   }

   /**
    * Remove the current object from the array.
    * Not implemented.
    *
    * @exception UnsupportedOperationException
    * @exception IllegalStateException
    */
   public void remove() throws UnsupportedOperationException , IllegalStateException {
      throw new UnsupportedOperationException();
   }

  
   public static void main ( String[] args ) {
      if ( debugging ) {
         String[] fruits = new String [] { "apple" , "orange" , "apricot"};
         for ( Iterator iter = new SimpleArrayIterator( fruits ); iter.hasNext(); ) {
            String key = (String) iter.next();
            System.out.println( key );
            }
         }
      }
   }

Output of Above Java Program
apple
orange
apricot

[ Read More ]

Java Program to Demonstrate the TreeSet

Here is a Java Program to Demonstrate the TreeSet

import java.util.Iterator;
import java.util.SortedSet;
import java.util.TreeSet;

class SSorted {
  public static void main(String[] argv) throws Exception {
    SortedSet<String> set = new TreeSet<String>();
    set.add("b");
    set.add("c");
    set.add("a");

    Iterator it = set.iterator();
    while (it.hasNext()) {
       Object element = it.next();
 System.out.println(element);
    }
    String[] array = (String[]) set.toArray(new String[set.size()]);
  }
}

Output of Above Java Program
a
b
c

[ Read More ]

To Demonstate the AWT Frames in Java

Here is a Java Program to Demonstrate the Frame in AWT Java.

import java.awt.*;
import java.awt.event.*;

class MyFrame extends Frame implements WindowListener, ActionListener{
 Button b1,b2,b3,b4,b5;
 public MyFrame(String title) {
  super(title);
  setSize(200,100);
  setVisible(true);
  addWindowListener(this);
  
  setLayout(new BorderLayout());
  b1=new Button("North");
  add(b1,BorderLayout.NORTH);
  b2=new Button("South");
  add(b2,BorderLayout.SOUTH);
  b3=new Button("East");

  add(b3,BorderLayout.EAST);
  b4=new Button("West");
  add(b4,BorderLayout.WEST);
  b5=new Button("Center");
  add(b5,BorderLayout.CENTER);
  b1.addActionListener(this);
  b2.addActionListener(this);
  b3.addActionListener(this);
 }

 public void windowOpened(WindowEvent we){} 
 
 public void windowClosing(WindowEvent we){
  dispose();
 } 
 public void windowClosed(WindowEvent we) {}
 public void windowActivated(WindowEvent we) {}
 public void windowDeactivated(WindowEvent we) {}
 public void windowIconified(WindowEvent we) {}
 public void windowDeiconified(WindowEvent we){} 

 public void actionPerformed(ActionEvent ae) {
  if(ae.getSource()==b1)
   javax.swing.JOptionPane.showMessageDialog(this,"Left");

  if(ae.getSource()==b2)
   javax.swing.JOptionPane.showMessageDialog(this,"Center");

  if(ae.getSource()==b3)
   javax.swing.JOptionPane.showMessageDialog(this,"Right");
 }

 public static void main(String args[]) {
  MyFrame frm=new MyFrame("My Frame");
 }
}

Output of Above Java Program

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Java Program to Demonstrate the Method Override

Here is a Java Program to Demonstrate the Method Override

class A {
  int i, j;
  A(int a, int b) {
    i = a;
    j = b;
  }
  // display i and j
  void show() {
    System.out.println("i and j: " + i + " " + j);
  }
}
class B extends A {
  int k;
  B(int a, int b, int c) {
    super(a, b);
    k = c;
  }
  // display k -- this overrides show() in A
  void show() {
    System.out.println("k: " + k);
  }
}
  
class Override{
  public static void main(String args[]) {
    B subOb = new B(1, 2, 3);
    subOb.show(); // this calls show() in B
  }
}

Output of Above Java Program
k: 3

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To Demonstrate the Calling of Constructor

Here is a Java Program to Demonstrate the Calling of Constructor.

// Create a super class.
class A {
  A() { 
    System.out.println("Inside A's constructor.");
  }
}

// Create a subclass by extending class A.
class B extends A {
  B() {
    System.out.println("Inside B's constructor.");
  }
}

// Create another subclass by extending B.
class C extends B {
  C() {
    System.out.println("Inside C's constructor.");
  }
}
  
class CallingCons {
  public static void main(String args[]) {
    C c = new C();
  }
}

Output of Above Java Program
Inside A's constructor.
Inside B's constructor.
Inside C's constructor.

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