Page Navigator in Java

This component is used for navigating through records in cases where the results set is huge and records are displayed as set of records of some predefined size.

Features
- Easy navigation of records
- User can configure the no of records per page

public class PageNavigator {


    int min =1, max,total , recSize;

    /**
  * This is the constructor
  * @param sRecSize the numer of records to display in a page.
     */

     public PageNavigator(int sRecSize)
      {
     this.recSize = sRecSize;
     this.max= sRecSize;
       }


    /**
     * function to decrement the records set when the 'Next' button is clicked
     */

    public void changeNextValue()
    {

         if(total==0)
         return;
         max=max+recSize;
         min =max-(recSize-1);
         if (max >= total)
             {
                max=total;
                min=(max/recSize)*recSize +1;
             }

         if(min>total)
            {
            min =max-(recSize-1);
            }



       }

    /**
     * function to decrement the records set when the 'Prev' button is clicked
     */

        public void changePrevValue() {
        int test = max;
        if(total==0) return;

        max=max-recSize;
        min=min-recSize;

        if (min< 0)
        {
         min=1;
         }


         if(test%recSize !=0 )
         {
             max=test-(test%recSize);


         }
            if(max >total )
                max=total;
            if( max <=0 )   max=recSize;
            if( total <recSize )
            max=total;


        }

    /**
     * function to get the first set of records or the First page
     */
     public void changeToFirstPage()
     {

         if(total==0) { min=max=0;return; }
         min = 1 ;
         max=recSize;
         if (total<= recSize && total >0)
         {
          max=total;

          }

         }

    /**
     * function to get the last set of records or the Last page
     */
     public void changeToLastPage()
     {

         if(total==0) { min=max=0;return; }

         max=total;
         int pageNo = total/recSize;
         min  =   pageNo*recSize +1 ;
         if (total<= recSize)
         {
          min=1;
         }



      }
    /**
     * Retrieve the total count of records based on the parameters.Function gets the generated query and updates the value of variable 'total' to the number of records.
     *
     * @param  selectStmt List the colums to be retrieved from table.
     * @param  tableName List the table to select the value from.
     * @param  isWhereClausePresent Determin if a Where clause exist for the query.
     * @param  WhereClause   The dynamically constructed query string to append to the where clause
     *
     */



    public void getTotalCount(String selectStmt,String tableName , boolean isWhereClausePresent,String WhereClause)
    {
           if(isWhereClausePresent)
           {
           String query = "select "+selectStmt+ " from "+tableName +"Where " +WhereClause;
           }
           else
           {
               String query = "select "+selectStmt+ " from "+tableName + "";
           }


           //Run the query and get the total count


           if(total<recSize && total>0)
           {
           min = 1;
           max= total;
           }
           if(total==0) min =0;max =0;

        }


   /**
  * Retrieve records based on the parameters . Function executes the generated query and retrieve the results
  *
  * @param  selectStmt List the colums to be retrieved from table.
  * @param  tableName  List the table to select the value from.
  * @param  isWhereClausePresent  Determin if a Where clause exist for the query.
  * @param  WhereClause   The dynamically constructed query string to append to the where clause
  *
  *
  */


       public void getRecordSet(String selectStmt,String tableName , boolean isWhereClausePresent,String WhereClause)
       {
   if(isWhereClausePresent)
           {
         String query = "SELECT * FROM (select " +selectStmt +",ROWNUM ROWIDX from " +tableName+ " WHERE "+WhereClause +"  ) WHERE  ROWIDX >=" +min+" AND ROWIDX <="+max;
         }
         else
         {
     String query = "SELECT * FROM (select " +selectStmt +",ROWNUM ROWIDX from " +tableName+ " ) WHERE  ROWIDX >=" +min+" AND ROWIDX <="+max;
      }

       }



  /**
   * Determine which navation to take from any of these : 'First','Prev','Next','Last'
   *
   * @param  buttonType determine which page to navigate to.
   *
   */

    public void buttonAction(int buttonType)
    {

  switch (buttonType)
  {
    case 1: changeToFirstPage();getRecordSet("*" ,"testTable" , true , "age>30"); break;
    case 2: changePrevValue();getRecordSet("*" ,"testTable" , true , "age>30"); break;
    case 3: changeNextValue();getRecordSet("*" ,"testTable" , true , "age>30"); break;
    case 4: changeToLastPage();getRecordSet("*" ,"testTable" , true , "age>30"); break;

  }

    }

       /*
        * The  number of records to display in a page can be made configurable.
        *
        */

    public static void main(String[] args) {

        int pageSize =100; //used to set the records per page

        PageNavigator pageNavigator = new PageNavigator(pageSize);

        pageNavigator.getTotalCount("*" ,"userdetails" , true , "age>30"); //Specify the fileds to be selected , the table  and the where Clause if any.
        pageNavigator.getRecordSet("*" ,"testTable" , true , "age>30");
            //The navigation  First ,Prev , Next ,Last can be some actions/ button /links in the page
        pageNavigator.buttonAction(3); //Calling Next  to return next set of records

        }
}