How to set a JPanel over a JFrame?

问题

I have a class named BoardGUI extended from JFrame, in a constructor I have made a JPanel with two buttons in it. I have added this panel into my frame. Whenever I run this program, buttons get invisible. As I bring my mouse cursor over the buttons they get visible. Code is as follows:

public class BoardGUI extends JFrame {
Play pieces;
JButton a=new JButton("Undo");
JButton r=new JButton("replay");
JPanel jp=new JPanel();

public BoardGUI() {
    pieces = new Play();
    setTitle("Checkers Game");
    setSize(645, 700);
    setVisible(true);

    jp.setLayout(new FlowLayout());
    jp.setPreferredSize(new Dimension(645,35));
    a.setVisible(true);
    r.setVisible(true);
    jp.add(a);
    jp.add(r);
    add(jp,BorderLayout.SOUTH);

I am also using repaint method in my program. Can anybody point out my mistake and suggest any solution for this?

回答1:

I have a class named BoardGUI extended from JFrame, in a constructor i have made a JPanel with two buttons in it. I have added this panel into my frame. Whenever i run this program, buttons get invisible. As i bring my mouse cursor over the buttons they get visible.

setVisible(true); should be last code line in constructor, because you added JComponents to the already visible JFrame,
or to call revalidate() and repaint() in the case that JComponents are added to visible Swing GUI
there no reason to call a.setVisible(true); or r.setVisible(true); for standard JComponents, because JComponents are visible(true) by default in comparing with Top Level Containers, there you need to call JFrame/JDialog/JWindow.setVisible(true);

EDIT

(i used the very first suggestion you gave. problem remains the same.) - for example

from code

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class MyGridLayout {

    private JFrame frame = new JFrame("GridLayout, JButtons, etc... ");
    private JPanel panel = new JPanel(new GridLayout(8, 8));

    public MyGridLayout() {
        for (int row = 0; row < 8; row++) {
            for (int col = 0; col < 8; col++) {
                JButton button = new JButton("(" + (row + 1) + " / " + (col + 1) + ")");
                button.putClientProperty("column", col);
                button.putClientProperty("row", row);
                button.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        JButton btn = (JButton) e.getSource();
                        System.out.println(
                                "clicked column : "
                                + btn.getClientProperty("column")
                                + ", row : " + btn.getClientProperty("row"));
                    }
                });
                panel.add(button);
            }
        }
        frame.add(panel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocation(150, 150);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                MyGridLayout myGridLayout = new MyGridLayout();
            }
        });
    }
}

来源：https://stackoverflow.com/questions/21112572/how-to-set-a-jpanel-over-a-jframe

标签

java

swing

jframe

jpanel