How to change Flowlayout via ItemListener

Question

I can not use grouped Checkbox to change FlowLayout's alignment. I'm sure select the checkbox will be into the "itemStateChanged" method, but .setAlignment() or .setLayout() both doesn't work!! Has any method to resolve this problem? thank you.

import java.awt.*;
import java.awt.event.*;
public class flowlayout
{
static Checkbox cb1 = new Checkbox("Left");
static Checkbox cb2 = new Checkbox("Center");
static Checkbox cb3 = new Checkbox("Right");    
static Frame frm = new Frame("Frame Title");    

public static void main(String args[])  {
    frm.setLayout(new FlowLayout());
    CheckboxGroup cg = new CheckboxGroup();
    cb1.setCheckboxGroup(cg);
    cb2.setCheckboxGroup(cg);
    cb3.setCheckboxGroup(cg);       
    cb1.addItemListener(new ItmLis());
    cb2.addItemListener(new ItmLis());
    cb3.addItemListener(new ItmLis());      
    frm.setSize(400,200);
    frm.add(cb1);
    frm.add(cb2);
    frm.add(cb3);   
    frm.setVisible(true);       
}   

static class ItmLis implements ItemListener
{
    public void itemStateChanged(ItemEvent e)
    {
        if(cb1.getState()==true)
        {
            frm.setLayout(new FlowLayout(FlowLayout.LEFT));
        }
        else if(cb2.getState())
        {
            frm.setLayout(new FlowLayout(FlowLayout.CENTER));
        }
        else if(cb3.getState())
        {
            frm.setLayout(new FlowLayout(FlowLayout.RIGHT));
        }
    }
}
}

Answer 1

• LayoutManager haven't implemented notifiers that there is relayout for any, part or whole container

• have to notify LayoutManager by container.validate(); and container.repaint(); (in Java7 to use revalidate() for JFrame too)

• have to kill current JVM instance by add WindowKistener (only overrode kill JVM there)

• use Swing over the prehistoric AWT

AWT version

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

public class MyFlowLayout {

    static Checkbox cb1 = new Checkbox("Left");
    static Checkbox cb2 = new Checkbox("Center");
    static Checkbox cb3 = new Checkbox("Right");
    static Frame frm = new Frame("Frame Title");

    public MyFlowLayout() {
        frm.setLayout(new FlowLayout());
        CheckboxGroup cg = new CheckboxGroup();
        cb1.setCheckboxGroup(cg);
        cb2.setCheckboxGroup(cg);
        cb3.setCheckboxGroup(cg);
        cb1.addItemListener(new ItmLis());
        cb2.addItemListener(new ItmLis());
        cb3.addItemListener(new ItmLis());
        frm.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        frm.setSize(400, 200);
        frm.add(cb1);
        frm.add(cb2);
        frm.add(cb3);
        frm.setVisible(true);
    }

    public static void main(String args[]) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                MyFlowLayout fs = new MyFlowLayout();
            }
        });
    }

    private class ItmLis implements ItemListener {

        @Override
        public void itemStateChanged(ItemEvent e) {
            if (cb1.getState() == true) {
                frm.setLayout(new FlowLayout(FlowLayout.LEFT));
                validateLayout();
            } else if (cb2.getState()) {
                frm.setLayout(new FlowLayout(FlowLayout.CENTER));
                validateLayout();
            } else if (cb3.getState()) {
                frm.setLayout(new FlowLayout(FlowLayout.RIGHT));
                validateLayout();
            }
        }

        public void validateLayout() {
            frm.validate();
            frm.repaint();
        }
    }
}

Swing version

import java.awt.*;
import java.awt.event.*;
import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JRadioButton;
import javax.swing.SwingUtilities;

public class MyFlowLayout {

    static JRadioButton cb1 = new JRadioButton("Left");
    static JRadioButton cb2 = new JRadioButton("Center");
    static JRadioButton cb3 = new JRadioButton("Right");
    static JFrame frm = new JFrame("Frame Title");

    public MyFlowLayout() {
        frm.setLayout(new FlowLayout());
        ButtonGroup cg = new ButtonGroup();
        cg.add(cb1);
        cg.add(cb2);
        cg.add(cb3);
        cb1.addItemListener(new ItmLis());
        cb2.addItemListener(new ItmLis());
        cb3.addItemListener(new ItmLis());
        frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        // or WindowListener too
        /*frm.addWindowListener(new WindowAdapter() {
         @Override
         public void windowClosing(WindowEvent e) {
         System.exit(0);
         }
         });*/
        frm.setSize(400, 200);
        frm.add(cb1);
        frm.add(cb2);
        frm.add(cb3);
        frm.setVisible(true);
    }

    public static void main(String args[]) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                MyFlowLayout fs = new MyFlowLayout();
            }
        });
    }

    private class ItmLis implements ItemListener {

        @Override
        public void itemStateChanged(ItemEvent e) {
            if (cb1.isSelected() == true) {
                frm.setLayout(new FlowLayout(FlowLayout.LEFT));
                validateLayout();
            } else if (cb2.isSelected() == true) {
                frm.setLayout(new FlowLayout(FlowLayout.CENTER));
                validateLayout();
            } else if (cb3.isSelected() == true) {
                frm.setLayout(new FlowLayout(FlowLayout.RIGHT));
                validateLayout();
            }
        }

        public void validateLayout() {
            frm.validate();
            frm.repaint();
        }
    }
}