如何使jPanel半透明？

Question

I want to add a jPanel which is semi transparent. But other components which are placed inside the jPanel such as buttons and labels should be displayed with 100% opacity. I am using netbeans to design the GUIs. Normally i drag and drop the swing components in the palette to design the GUI(I don't code them). I can't see any property in properties window to achieve this. Please help me. As I am quite new to java please give me a detailed answer. Thanks in advance.

Answer 1

You can use JPanel.setBackground(Color bg); to make the panel semi-transparent. What matter is the color's property. You can construct a color with alpha values to set the transparent degree of the color.

panel.setBackground(new Color(213, 134, 145, 123));

The last parameter is actual the alpha value and you can adjust it to see the effect.

Here is the code:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;

import javax.swing.BorderFactory;
import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class PanelTest {
    public static void main(String[] args) {

        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                PanelTest test = new PanelTest();
                test.createUI();
            }
        };
        SwingUtilities.invokeLater(runnable);
    }

    public void createUI(){
        JFrame frame = new JFrame("Panel Test");

        JPanel panel = new JPanel();

        panel.setBackground(new Color(213, 134, 145, 123));
        JButton button = new JButton("I am a button");

        JLabel label = new JLabel("I am a label");
        label.setFont(new Font("Arial", Font.BOLD, 15));

        JTextField textField = new JTextField();

        panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
        panel.add(button);
        panel.add(Box.createVerticalStrut(20));
        panel.add(label);
        panel.add(Box.createVerticalStrut(20));
        panel.add(textField);

        panel.setBorder(BorderFactory.createEmptyBorder(30, 30, 30, 30));

        BottomPanel buttomPanel = new BottomPanel();
        buttomPanel.add(panel);
        frame.add(buttomPanel,BorderLayout.CENTER);

        frame.setResizable(false);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    @SuppressWarnings("serial")
    class BottomPanel extends JPanel{
        @Override
        protected void paintComponent(Graphics g) {
            for (int y = 0; y < 200; y = y + 20) {
                g.drawString("I am the string on the bottom", 5, y);
            }
        }
    }
}

Here is the effect and hope it can help you.

Answer 2

You can simply create your jPanel using drag and drop, as you always do and then for changing the panel's color and making it transparent or semi-transparent you can use this code:

panel.setBackground(new Color(0.0f, 0.0f, 0.0f, 0.5f));

You can change the color by changing first three parameters of Color constructor, which represent RGB and you can change transparency by changing fourth parameter, which is the alpha value of color.