java - JComponent 子类未出现

Question

好的。我正在编写我的 Ball 类，但球没有显示。我尝试将其他组件添加到我的容器中并且它们被显示，所以我认为可以安全地假设问题出在我的球上。类代码:

import java.awt.Color;
import java.awt.Graphics;

import javax.swing.JComponent;


public class Ball extends JComponent {

public Ball() {
    ballX  = (Window.WINDOW_WIDTH - BALL_DIAMETER) / 2;
    ballY  = (Window.WINDOW_HEIGHT - BALL_DIAMETER) / 2;
}

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawRect(5, 5, 50, 50);
    g.setColor(Color.GREEN);
    g.fillOval(ballX, ballY, BALL_DIAMETER, BALL_DIAMETER);
    g.dispose();

}
public void setX(int x) {
    ballX = x;
}
public void setY(int y) {
    ballY = y;
}

private int ballX;
private int ballY;
public static final int BALL_DIAMETER = 30;
}

第一个矩形用于测试。它也没有出现......

Answer 1

确保您的组件的首选尺寸大于 (0, 0):

@Override
public Dimension getPreferredSize() {
    return new Dimension(500, 500);
}