java - Animate ball JPanel subclass is not abstract错误

Question

我制作了一个简单的形状程序，它在 JPanel 中为球制作动画。我的公共(public)类形状标记错误，指出形状不是抽象的(请参见下面的屏幕截图)

Shape is not abstract and does not override abstract method actionPerformed(ActionEvent) in ActionListener

Abstract error Screenshot

形状.java:

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionListener;
import java.awt.geom.Ellipse2D;
import javafx.event.ActionEvent;
import javax.swing.*;

 public class Shape extends JPanel implements ActionListener {
    Timer t = new Timer(5, this);

    double x = 0;
    double y = 0;
    double velX = 2;
    double velY = 2;

   public void painComponent(Graphics g) {
       super.paintComponent(g);
       Graphics2D g2 = (Graphics2D) g;
       Ellipse2D circle = new Ellipse2D.Double(x, y, 40, 40);

       g2.fill(circle);
       t.start(); 
   }

   public void actionPerformed(ActionEvent e) {
       if (x < 0 || x > 560) {
           velX = -velX;
       }

       if(y < 0 || y > 360) {
           velY = -velY;
       }

       x += velX;
       y += velY;
       repaint();
   }
}

主要.java:

import javax.swing.JFrame;

public class Main {
    public static void main(String[] args) {
        Shape s = new Shape();
        JFrame f = new JFrame();
        f.add(s);
        f.setVisible(true);
        f.setSize(600,400);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setTitle("Moving Ball");
    }
}

Answer 1

取而代之的是:

import javafx.event.ActionEvent;

你可能想要这个:

import java.awt.event.ActionEvent;

在 paintComponent() 和 actionPerformed() 的实现中，使用 @Override ，它“通知编译器该元素旨在覆盖父类(super class)中声明的元素。”然后，编译器可以帮助您识别拼写和类型错误。

public class Shape extends JPanel implements ActionListener {
    …
    @Override
    public void paintComponent(Graphics g) {…}

    @Override
    public void actionPerformed(ActionEvent e) {…}
}

您可以覆盖 getPreferredSize() 以反射(reflect)您选择的几何形状。此外，请考虑重构数字常量。

@Override
public Dimension getPreferredSize() {
    return new Dimension(560, 360);
}