paintComponent（）方法不绘制到JPanel

Question

将显示JFrame和JPanel，但paintComponent方法不在JPanel上绘制。我只看到我添加的JLabel、JTextField和JButton，而没有看到应该在JPanel上绘制的内容。

package h02;

import javax.swing.*;

public class Circles extends JFrame {

    public Circles() {

    // JFrame and its properties

    JFrame frame = new JFrame();

    frame.setSize(500,500);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLocation(100, 100);
    frame.setTitle("Circles");
    frame.add(new CirclesPanel());
    frame.setVisible(true);

}

public static void main(String[] args) {

        new Circles();
    }

}

    package h02;

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

    public class CirclesPanel extends JPanel implements ActionListener {

        // Fields

    private JTextField enterDiameter;
    private JButton drawButton;
    private int diameter;
    private final int Y = 470;

    // making the panel

    public CirclesPanel() {

        enterDiameter = new JTextField("100", 5);
        enterDiameter.addActionListener(this);
        drawButton = new JButton("Teken");
        drawButton.addActionListener(this);
        add(new JLabel("Diameter"));
        add(enterDiameter);
        add(drawButton);

    }

    // find the diameter

    public void findDiameter() {

        int diameterString = Integer.parseInt(enterDiameter.getText());
        diameter = diameterString;
    }

    // draw circles


    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        int centre = getWidth() / 2;
        g.drawLine(30, Y, Y , Y);
        g.setColor(Color.ORANGE);
        g.fillOval(centre, Y, diameter, diameter);
        g.setColor(Color.BLACK);
        g.drawOval(centre, Y, diameter, diameter);
        g.drawOval(centre, Y, diameter / 2, diameter);
    }

    // on action performed...

    public void actionPerformed(ActionEvent e) {
        findDiameter();
        repaint();
    }

}

Answer 1

问题是圆圈中的“Y”。元素是绘制的，但在框架之外，尝试减少Y，你肯定会看到你的元素。

或者增加帧大小。