java-JPanel上的组件未显示

我创建了一个JPanel,并对其进行了一些修改.我将其背景更改为渐变颜色,这是该类.

public class JGradientPanel extends JPanel {
     private static final int N = 32;
     private Color color1, color2;
        public JGradientPanel(Color color1, Color color2) {
            this.setBorder(BorderFactory.createEmptyBorder(N, N, N, N));

            this.color1 = color1;
            this.color2 = color2;
        }

        @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);
        }
}

现在我在面板上添加了一些组件,但是它什么都没有显示,这是代码

public JPanel getMenu() {
        JGradientPanel menu = new JGradientPanel(Color.WHITE, Color.white.darker());
        int menuHeight = (int) ((int) getHeight() * 0.07);
        menu.setPreferredSize(new Dimension(screenWidth,menuHeight));
        menu.setLayout(new GridLayout(1,10));
        menu.setBackground(Color.LIGHT_GRAY);

        //test
        JGradientButton test = new JGradientButton("test",Color.GREEN, Color.BLUE);
        menu.add(test);

        JLabel space = new JLabel(); // first blank space on the menu
        space.setBounds(0, 0, menu.getPreferredSize().width - 50, menu.getPreferredSize().height);
        space.setBorder(BorderFactory.createMatteBorder(0, 0, 0, 1, Color.GREEN));
        menu.add(space);
        JLabel moreSpaces[] = new JLabel[6];
        buttons = new JButton[buttonLabels.length];
        for(int counter = 0; counter < moreSpaces.length + buttonLabels.length; counter ++ ) {
            if(counter < 3) {
                buttons[counter] = new JButton(buttonLabels[counter]); //menu buttons

            } else {
                moreSpaces[counter - 3] = new JLabel(); // the rest of the blank in the menu
            }
        }
        // adding components to menu panel
        for(int counter = 0; counter < moreSpaces.length + buttonLabels.length; counter ++){
            if(counter < 3) {
                buttons[counter].setFocusPainted(false);
                menu.add(buttons[counter]); 
            } else {
                menu.add(moreSpaces[counter - 3]);
            }

        }
        return menu;
    }

我错过了什么还是做错了吗？我的代码有什么问题？

解决方法:

>在公共类JGradientPanel中覆盖getPreferredSize扩展了JPanel {
> Painting in Swing,由public void paintComponent(Graphics g){默认情况下永远不会返回PreferredSize to JPanel,
> JPanel返回Dimension [0,0];

编辑

>见识详实和interesting thread about GradientPaint

标签：paintcomponent,java,swing,jpanel,preferredsize
来源： https://codeday.me/bug/20191009/1878588.html