simple program but not able to get the required output

[vamsi naki]

Hi,
i wrote a simple code that changes the color of the frame when the button is clicked ,the thing is when i run the program i am getting the output of the previous program (a frame that just displays a button) which i wrote .I am using eclipse indigo .Eclipse says there is an error in the project but where the error is it is not showing.

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

public class redorgreen {

	public static void main(String []args)
	{
		test t =new test();
	    	
	}
}

class test extends JFrame implements ActionListener
{

	test()
	{
	setSize(500, 500);
	setVisible(true);
	setLayout(new FlowLayout());
	JButton red=new JButton();
	JButton green =new JButton();
	red.setActionCommand("red");
	green.setActionCommand("green");
	red.addActionListener(this);
	green.addActionListener(this);
	
	
	
	setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	}
	
	public void actionPerformed(ActionEvent evt)
	{
	if(evt.getActionCommand().equals("red"))
	{
		getContentPane().setBackground(Color.red);
	repaint();
	}
		else
		getContentPane().setBackground(Color.green);
	repaint();
	}
			
}

[Shtilmark Pollo]

I think your code must be something like that:

public class RedOrGreen extends JFrame implements ActionListener {   
    public RedOrGreen() {
	setSize(500, 500);  
	setVisible(true);  
	setLayout(new FlowLayout());  
	setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
	JButton red=new JButton("red");  
	JButton green =new JButton("green");  
	red.addActionListener(this);  
	green.addActionListener(this);
	add(red);
	add(green);
    }

      
    public void actionPerformed(ActionEvent evt) {  
	if(evt.getActionCommand().equals("red"))
	    getContentPane().setBackground(Color.red);  
	else  
	    getContentPane().setBackground(Color.green);  
	repaint();  
    } 

    public static void main(String []args) {  
	SwingUtilities.invokeLater(new Runnable() {
		public void run() {
		    RedOrGreen t = new RedOrGreen();  
		    t.pack();
		    t.setVisible(true);
		}
	    });
    }  
} 

[Hitesh P Patel]

vamsi naki wrote:when the button is clicked

How you are getting Button in frame without adding it to container ?

[Campbell Ritchie]

Eclipse should always show you where the error is, with a little red icon with a cross in. Hover your mouse over that and you get more details. What it cannot tell you is whether you are using object‑oriented design or not, and that isn’t even close! In my opinion addActionListener(this) is an abomination against object‑oriented programming, and all the people who write books using it ought to be strung up and beaten with several megabytes of C code

Start here. You will want some sort of class. How about this?

package ...
import ...

/**
 * blah blah blah
 */
public class ColourListener implements ActionListener
{
   private final Component comp;
   private final Color colour;

   /**
    * yadayadayada...
    */
   public ColourListener(Component comp, Color colour)
   {
      this.comp = comp;
      this.colour = colour;
   }

 
   /**
    * rhubarb rhubarb rhubarb...
    */
  public void actionPerformed(ActionEvent evt)
   {
       comp.....
   }
}

There are obviously bits you will have to fill in for yourself. Search for my posts on this forum with “ColourListener” as a keyword, and you will find more. But I don’t think you will find a complete class.

[Campbell Ritchie]

Welcome to the Ranch Shtilmark Pollo.

If you are using the action command without setting it, won’t you suffer a null pointer exception?

[Shtilmark Pollo]

Campbell Ritchie wrote:Welcome to the Ranch Shtilmark Pollo.

Gracias:)

Campbell Ritchie wrote:
If you are using the action command without setting it, won’t you suffer a null pointer exception?

I dont think so. If action command not set then getActionCommand return button text.
From javax.swing.AbstractButton

    public String getActionCommand() {
        String ac = getModel().getActionCommand();
        if(ac == null) {
            ac = getText();
        }
        return ac;
    }

[vamsi naki]

Hitesh P Patel wrote:

vamsi naki wrote:when the button is clicked

How you are getting Button in frame without adding it to container ?

i should have checked i forgot to add the buttons to the container


Thanks Campbell Ritchie ,Shtilmark Pollo and Hitesh P Patel .I have to go through a lot of topics in GUI i guess,cause i dont know anything about ColourListener.I will refer to your posts Campbell Ritchie.