CODEWITHSUNDEEP
javaswingjpanel
adi1ya
adi1ya

Reputation: 402

Why the color of JPanel not changing even when the button is clicked?

I am doing Head First Java when I stumbled upon this problem and I don't know how to solve it.

I want to change the color of my JPanel widget when the button is clicked I am using Mac OS. 

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

public class SimpleGui implements ActionListener {
    JFrame frame;
    JButton button;

    public static void main(String[] args) {
        SimpleGui gui = new SimpleGui();
        gui.go();
    } //close main

    public void go() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        button = new JButton("changes colour");
        button.addActionListener(this);

        MyPanel drawPanel = new MyPanel();

        frame.getContentPane().add(BorderLayout.SOUTH,button);
        frame.getContentPane().add(BorderLayout.CENTER,drawPanel);

        frame.setSize(300, 300);
        frame.setVisible(true);
   } //close go


    public void actionPerformed(ActionEvent event) {
        frame.repaint();
        button.setText("color changed");
    }
} // close actionPerformed

// the widget whose color i want to change 
class MyPanel extends JPanel {

    public void paintComponent(Graphics g) {
        g.setColor(Color.green); // i choose green as a color 
        g.fillRect(20, 50, 100, 100);
    } //close paintComponent
} //close MyPanel

Upvotes: 0

Views: 113

Answers (2)

camickr
camickr

Reputation: 324118

but the JFrame widow have green rectangle even before i click on the button.

That is because you already hard code the color green in the paintComponent method. So it will always be green.

Your class should have a property to set the color of the rectangle. Something like:

class MyPanel extends JPanel 
{
    private Color rectangleColor = getBackground();

    @Override
    public void paintComponent(Graphics g) 
    {
        super.paintComponent(g);

        g.setColor( rectangleColor); // i choose green as a color 
        g.fillRect(20, 50, 100, 100);
    }

    public void setRectangleColor(Color rectangleColor)
    {
        this.rectangleColor = rectangleColor;
        repaint();
    }
}

Then in the ActionListener of the button you use:

//frame.repaint();
drawPanel.setRectangleColor( Color.GREEN );
button.setText("color changed");

The 'drawPanel` variable will also need to be an instance variable in your class.

Now with this design you could have multiple buttons. Each button could change the rectangle to a different color.

Upvotes: 1

Parsamlm
Parsamlm

Reputation: 72

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

public class SimpleGui implements ActionListener {
JFrame frame;
JButton button;

public static void main(String[] args) {
    SimpleGui gui = new SimpleGui();
    gui.go();
} //close main

public void go() {
    frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    button = new JButton("changes colour");
    button.addActionListener(this);

    MyPanel drawPanel = new MyPanel();

    frame.getContentPane().add(BorderLayout.SOUTH,button);
    frame.getContentPane().add(BorderLayout.CENTER,drawPanel);

    frame.setSize(300, 300);
    frame.setVisible(true);
   } //close go


@Override
public void actionPerformed(ActionEvent event) {
    frame.repaint();
    button.setText("color changed");
}
} // close actionPerformed

// the widget whose color i want to change 
class MyPanel extends JPanel {
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    this.setBackground(Color.white);
    g.setColor(Color.green); // i choose green as a color 
    g.fillRect(20, 50, 100, 100);
} //close paintComponent
} //close MyPanel

paintCompenent should be paintComponent

Upvotes: 1

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