How to make the background gradient of a JPanel

Question

I want to know how to make background gradient which is in another JPanel. Many articles found in internet,but all of them had demostrated how to overide the paintComponent() of the JPanel not how to do for a jPanel which is inside it.
I use Netbeans IDE. I created a new JPanel class and could overide its paintComponent(). I have another jpanel on it (dragged & dropped on to the parent JPanel). I want to make its background gradient.

Here is how I tried for parent. It worked. How can I overide this for child jpanel ?

public void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        Color color1 = getBackground();
        Color color2 = color1.darker();
        int w = getWidth();
        int h = getHeight(); 
        GradientPaint gp = new GradientPaint(
                0, 0, color1,
                0, h, color2);

        g2d.setPaint(gp);
        g2d.fillRect(0, 0, w, h);
        }

Solution 1

If you are careful to invoke super.paintComponent(g), you can add the gradient directly to the panel as shown below.

For usability, I would resist the temptation to try making the individual components transparent. Note also that opacity is controlled by the Look & Feel.

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

/**
* @see http://stackoverflow.com/q/12220853/230513
*/
public class GradientPanel extends JPanel {

    private static final int N = 32;

    public GradientPanel() {
        this.setBorder(BorderFactory.createEmptyBorder(N, N, N, N));
        this.add(new JLabel("Test:", JLabel.CENTER));
        this.add(new JTextField("This is a test."));
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        Color color1 = getBackground();
        Color color2 = color1.darker();
        int w = getWidth();
        int h = getHeight();
        GradientPaint gp = new GradientPaint(
            0, 0, color1, 0, h, color2);
        g2d.setPaint(gp);
        g2d.fillRect(0, 0, w, h);
    }

    private void display() {
        JFrame f = new JFrame("GradientPanel");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new GradientPanel().display();
            }
        });
    }
}

Solution 2

I think this is what you were trying to do

jPanel1 = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                Graphics2D g2d = (Graphics2D) g;
                g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
                int w = getWidth();
                int h = getHeight();
                Color color1 = new Color(81,80,106);
                Color color2 = new Color(165,164,241);
                GradientPaint gp = new GradientPaint(0, 0, color1, 0, h, color2);
                g2d.setPaint(gp);
                g2d.fillRect(0, 0, w, h);
            }
        };

Comments

[Débora]

thanks for your answer. What you have mentioned is already implemented for my parent JPanel( the codes also mentioned in my question). What I ask is, lets say, if another JPanel is required to add to your 'GradientPanel'. and make its background gradient. Then how it can be done ?

[trashgod]

Ah, you want to alter the background of a JPanel for which you do not have source code access. You could use UIManager.put() to supply your own PanelUI with a custom implementation of paint().