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Easy Question (URGENT Please) ....

Hi,
I am new in Java. I have writtena Java program that gives an user-interface.
I have made two JPanels. One JPanel (top) is used for drawing area and the lower JPanel is used for some JButtons, JTextField and one JList. Everything works perfrctly except the ActionListener of the JList...
When I add the ActionListener for the JList, it gives the following error:
"interface javax.swing.event.ListSelectionListener is an abstract class. It cannot be instantiated.
new ListSelectionListener()."
I am new in Java, if you have any suggestion to fix it, please modify the lines in my code.
I have written within /*...*/ the line of codes, creating the problem.
Thanks..
Here is my complete code (In single file):
//***********************************
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.util.*;

public class CustomPanelTest extends JFrame {
private JPanel buttonPanel;
private CustomPanel myPanel;
private JButton b1, b2, b3;
private JTextField t1;
private JList randomList;
public static int myint=0;
String mychoice = "random";

private String randomNames[] =
{ "one", "two", "three",
"four", "five", "six" };

public CustomPanelTest()
{
super( "CustomPanel Test" );

myPanel = new CustomPanel(); // instantiate canvas
myPanel.setBackground( Color.green );

b2 = new JButton( "Clear" );
b2.addActionListener(
new ActionListener() {
public void actionPerformed( ActionEvent e )
{
myint=0;
myPanel.draw( CustomPanel.CIRCLE );
}
}
);

b1 = new JButton( "Draw" );
b1.addActionListener(
new ActionListener() {
public void actionPerformed( ActionEvent e )
{
if (myint == 0)
myint = 250;
myPanel.draw( CustomPanel.CIRCLE );
} }
);

b3 = new JButton( "About");
b3.addActionListener(
new ActionListener() {
public void actionPerformed( ActionEvent e )
{
JOptionPane.showMessageDialog( null,
"Robert\n" + "Login: vle" );

}
}
);

t1 = new JTextField( 10 );
t1.addActionListener(
new ActionListener() {
public void actionPerformed( ActionEvent e )
{
myint = 250;
myint = Integer.parseInt( e.getActionCommand() );
}
}
);

// create a list with the items in the colorNames array
randomList = new JList( randomNames );
randomList.setVisibleRowCount( 1 );
randomList.setSelectionMode( ListSelectionModel.SINGLE_SELECTION );
/*
//Following code creating problem...
randomList.addListSelectionListener(
new ListSelectionListener() {
public void actionPerformed( ActionEvent e )
{
mychoice = "one";
mychoice = e.getActionCommand();

}
}
);

//Above code creating problem.. */

buttonPanel = new JPanel();
buttonPanel.setLayout( new GridLayout( 1, 5 ) );
buttonPanel.add( t1 );
buttonPanel.add( b1 );
buttonPanel.add( b2 ); buttonPanel.add( b3 );
buttonPanel.add( new JScrollPane( randomList ) );

Container c = getContentPane();
c.add( myPanel, BorderLayout.CENTER );
c.add( buttonPanel, BorderLayout.SOUTH );

setSize( 800, 450 );
show(); }

public static void main( String args[] )
{
CustomPanelTest app = new CustomPanelTest();

app.addWindowListener(
new WindowAdapter() {
public void windowClosing( WindowEvent e )
{ System.exit( 0 );
}
}
);
}
} class CustomPanel extends JPanel {
public final static int CIRCLE = 1;
public static int total;
CustomPanelTest myclass;
Random r = new Random();
int xval, yval;

public void paintComponent( Graphics g )
{
super.paintComponent( g );
for (int i=0; i<CustomPanelTest.myint; i++)
{
xval = r.nextInt() % 800;
yval = r.nextInt() % 450;

if (xval < 0)
xval -= 2*xval;

if (yval < 0)
yval -= 2*yval;

g.fillOval( xval, yval, 5, 5 );

}

}

public void draw( int s )
{
repaint();
}
}
//**********************************

tooki

ASKER

Adjusted points to 250

sankars98

ListSelectionListener doesnot contain
any method called "actionPerformed()"
You did not implement "valueChanged()"
method. That's why you are getting
this error.

list.addListSelectionListener( new ListSelectionListener(){
public void valueChanged( ListSelectionEvent e ){
if(e.getValueIsAdjusting())
System.out.println( ((JList)e.getSource()).getSelectedValue());
}
});

tooki

ASKER

Hi,
Thank you very much for helping me. Yes, ListSelectionListener does not conatin any method named "actionPerformed()", but this is one function, I have declared, and it has been defined there itself. Please see the ActionListener() code for the JButton b1(the ActionListener of b1 works perfectly), where similarly I have declared a local function named "actionPerformed()". Also I have not used any method named "valueChanged()", however please IGNORE the above code, and following is the simplified code for the entire file. This code works PERFECTLY when the ActionListener part of the JList is OMITTED! The error with the ActionListener(while included) is the same, that I got previously.
Thanks alot...

Here is the complete code:
//***********************

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

public class CustomPanelTest extends JFrame {
private JPanel buttonPanel;
private CustomPanel myPanel;
private JButton b1;
private JList randomList;
String mychoice = "random";
private static int myint=0;

private String randomNames[] =
{ "one", "two", "three",
"four", "five", "six" };

public CustomPanelTest()
{
super( "CustomPanel Test" );

myPanel = new CustomPanel(); // instantiate canvas
myPanel.setBackground( Color.green );

b1 = new JButton( "Draw" );
b1.addActionListener(
new ActionListener() {
public void actionPerformed( ActionEvent e )
{
if (myint == 0)
myint = 250;
myPanel.draw( CustomPanel.CIRCLE );

}
}
);

// create a list with the items in the colorNames array
randomList = new JList( randomNames );
randomList.setVisibleRowCount( 1 );
randomList.setSelectionMode( ListSelectionModel.SINGLE_SELECTION );
/*
//Following code creating problem...
randomList.addListSelectionListener(
new ListSelectionListener() {
public void actionPerformed( ActionEvent e )
{
mychoice = "one";
mychoice = e.getActionCommand();

}
}
);

//Above code creating problem.. */

buttonPanel = new JPanel();
buttonPanel.setLayout( new GridLayout( 1, 2 ) );
buttonPanel.add( b1 );
buttonPanel.add( new JScrollPane( randomList ) );

Container c = getContentPane();
c.add( myPanel, BorderLayout.CENTER );
c.add( buttonPanel, BorderLayout.SOUTH );

setSize( 800, 450 );
show(); }

public static void main( String args[] )
{
CustomPanelTest app = new CustomPanelTest();

app.addWindowListener(
new WindowAdapter() {
public void windowClosing( WindowEvent e )
{
System.exit( 0 );
}
}
);
}
}

class CustomPanel extends JPanel {
public final static int CIRCLE = 1;
public void paintComponent( Graphics g )
{
super.paintComponent( g );
g.fillOval( 10, 10, 5, 5 );
}

public void draw( int s )
{
repaint();
}
}

//********************************

ASKER CERTIFIED SOLUTION

Jod

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Jod

This version of the code will get you the selected value of the list - you will see it printed out - and put it into mychoice as a string.

//***********************

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

public class CustomPanelTest extends JFrame {
private JPanel buttonPanel;
private CustomPanel myPanel;
private JButton b1;
private JList randomList;
String mychoice = "random";
private static int myint=0;

private String randomNames[] =
{ "one", "two", "three",
"four", "five", "six" };

public CustomPanelTest()
{
super( "CustomPanel Test" );

myPanel = new CustomPanel(); // instantiate canvas
myPanel.setBackground( Color.green );

b1 = new JButton( "Draw" );
b1.addActionListener(
new ActionListener() {
public void actionPerformed( ActionEvent e )
{
if (myint == 0)
myint = 250;
myPanel.draw( CustomPanel.CIRCLE );

}
}
);

// create a list with the items in the colorNames array
randomList = new JList( randomNames );
randomList.setVisibleRowCount( 1 );
randomList.setSelectionMode( ListSelectionModel.SINGLE_SELECTION );

randomList.addListSelectionListener(
new ListSelectionListener() {
public void valueChanged( ListSelectionEvent e )
{
mychoice = (String)(((JList)e.getSource()).getSelectedValue());
System.out.println(mychoice);

}
}
);

buttonPanel = new JPanel();
buttonPanel.setLayout( new GridLayout( 1, 2 ) );
buttonPanel.add( b1 );
buttonPanel.add( new JScrollPane( randomList ) );

Container c = getContentPane();
c.add( myPanel, BorderLayout.CENTER );
c.add( buttonPanel, BorderLayout.SOUTH );

setSize( 800, 450 );
show(); }

public static void main( String args[] )
{
CustomPanelTest app = new CustomPanelTest();

app.addWindowListener(
new WindowAdapter() {
public void windowClosing( WindowEvent e )
{
System.exit( 0 );
}
}
);
}
}

class CustomPanel extends JPanel {
public final static int CIRCLE = 1;
public void paintComponent( Graphics g )
{
super.paintComponent( g );
g.fillOval( 10, 10, 5, 5 );
}

public void draw( int s )
{
repaint();
}
}
//********************************

sankars98

:-)))))

tooki , you have to include the
following checking condition inside
your valueChanged() function.
Because valueChanged() func. will
be called twice for a single click.
( 1st time for mouse down , 2nd
time mouse up )

if(e.getValueIsAdjusting())

sgoms

Lets get a few concepts right,

sgoms

/**** Event Model ****/
continued...

sgoms

having problems posting ...
please see,
https://www.experts-exchange.com/jsp/qShow.jsp?ta=java&qid=10236354

tooki

ASKER

Hi Jod, sankars98, Jod......

Thank you all very very much.....Thanks a lot for your great explanation...It works....
Still one small question:
Can you tell me why it prints "twice" on the STDOUT the value of "mychoice" for the statement: System.out.println(mychoice);
Also:
In the Public class of the program, I have written:
setSize(800, 450); However, when I execute the .class file and change the size of the screen by using mouse, how can I can I capture the changed size for oth in the x-axis and y-axis dircetion?
(It is helpful for me, because, I am drawing in my drawing area, JPanel and the size of what I draw is based on the setSize value. If I can get the new size, I can probably dynamically change the figure I draw... ..)

Thanks alot....
tooki

tooki

ASKER

Hi Jod, sankars98, sgoms....

Thank you all very very much.....Thanks a lot for your great explanation...It works....
Still one small question:
Can you tell me why it prints "twice" on the STDOUT the value of "mychoice" for the statement: System.out.println(mychoice);
Also:
In the Public class of the program, I have written:
setSize(800, 450); However, when I execute the .class file and change the size of the screen by using mouse, how can I can I capture the changed size for oth in the x-axis and y-axis
dircetion?
(It is helpful for me, because, I am drawing in my drawing area, JPanel and the size of what I draw is based on the setSize value. If I can get the new size, I can probably dynamically change
the figure I draw... ..)

Thanks alot....
tooki

Jod

See sankars comment further up, as the reason it is printing twice is my fault - you should have the code like this:

public void valueChanged( ListSelectionEvent e )
{

if(e.getValueIsAdjusting()) {
mychoice = (String)(((JList)e.getSource()).getSelectedValue());
System.out.println(mychoice);
}
}

....was getting tired so just posted code once it was working with no extras...

Jod

Oh yes, and to get the size of the JPanel you are drawing in to just do this:

class CustomPanel extends JPanel {
public final static int CIRCLE = 1;
public void paintComponent( Graphics g )
{
super.paintComponent( g );
int w = getWidth(); // width of panel
int h = getHeight(); // height of panel
g.fillOval( w/2, h/2, 5, 5 );
}

public void draw( int s )
{
repaint();
}
}

This will always draw you an oval in the middle of the panel - whatever size you scale it to.

So just scale your graphics relative to the current width and height of the component you are drawing in.

See! a nice short answer for a change...

tooki

ASKER

Hi Jod....

Thank you very very much...
tooki