import javax.swing.JOptionPane; import javax.swing.JFrame; import java.awt.Graph

ID: 3562607 • Letter: I

Question

import javax.swing.JOptionPane;
import javax.swing.JFrame;
import java.awt.Graphics;

public class PalindromeClient extends JFrame
{
private Palindrome palind;
boolean started = false;

public PalindromeClient( )
{
   palind = new Palindrome( );
   setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   setSize( 570, 400 );
   setVisible( true );
}

public Palindrome getPalindrome( )
{
return palind;
}

public void setStarted( boolean b )
{
started = b;
}

public boolean recursivePalindrome( String pal )
{
// ***** Student writes the body of this method *****

   // Using recursion, determine if a String representing
   // a word or a sentence is a palindrome
   // If it is, return true, otherwise return false

// We call the method animate inside the body of this method
// The call to animate is already coded below

animate( pal );

   //
   // Student code starts here
   //

      return true; // replace this dummy return statement
   //
   // End of student code
   //
}

public void animate( String pal )
{
   palind.updatePalindrome( pal );
   palind.setStarted( true );
   started = true;
   repaint( );
   try
   {
       Thread.sleep( 1000 );      // wait for the animation to finish
   }
   catch ( Exception e )
   {
   }
}

public void paint( Graphics g )
{
    if ( started )
    {
     super.paint( g );
     palind.draw( g );
    }
}

public String getPalString( )
{
boolean goodInput = false;
String palString = "";
// palString is limited to 26 characters
while ( !goodInput )
{
   try
   {
    palString = JOptionPane.showInputDialog( null, "Enter a word or phrase between 1 and 26 characters long" );
    if ( palString != null )
    {
     if ( palString.length( ) <= 26 && palString.length( ) >= 1 )
        goodInput = true;
    }
    else
    {
     System.exit( 0 );
    }
   }
   catch ( Exception e )
   { }
}
return palString;
}

public static void main( String [] args )
{
   PalindromeClient app = new PalindromeClient( );
   // ask user for input
   boolean result = false;

   // the program will loop until the user clicks on "Cancel"
   while ( true )
   {
    String appPal = app.getPalString( );
    ( app.getPalindrome( ) ).setPalString( appPal );
    app.setStarted( true );
    // start
    result = app.recursivePalindrome( ( app.getPalindrome( ) ).getPalString( ) );
    // finish last step in animation
    ( app.getPalindrome( ) ).setResult( result );
    app.repaint( );
    System.out.println( "The correct result is " + ( app.getPalindrome( ) ).getExactResult( ) );
    System.out.println( "Your result is " + result );
    System.out.println( "Done " );
    // done
    JOptionPane.showMessageDialog( null, "Done" );
   }
}
}

Explanation / Answer

if(pal.length() == 0 || pal.length() == 1)
// if length =0 OR 1 then it is
return true;
if(pal.charAt(0) == pal.charAt(pal.length()-1))
// check for first and last char of String:
// if they are same then do the same thing for a substring
// with first and last char removed. and carry on this
// until you string completes or condition fails
return recursivePalindrome(pal.substring(1, pal.length()-1));

// if its not the case than string is not.
return false;

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import javax.swing.JOptionPane; import javax.swing.JFrame; import java.awt.Graph

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