swing如何在java面板上移动图形元素？

Question

我目前正在做一个简单的类似乒乓球的游戏，但我被矩形的定位绊住了。 我想把它的Y位置改为实际面板高度的一半

package com.game;
import javax.swing.*;
import java.awt.*;

public class Main {

    public static void main(String[] args) {
        JFrame frame = new JFrame("gEngine");
        Player playerOne = new Player(frame);
        Player playerTwo = new Player(frame);
    }
}


package com.game;

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

public class Player {
    public Player(JFrame frame) {
        MyPanel panel = new MyPanel();
        frame.add(panel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setBackground(Color.BLACK);
        frame.setSize(1280, 720);
        frame.setVisible(true);
    }
}
class MyPanel extends JPanel {
    public void paintComponent(Graphics g) {
        g.setColor(Color.WHITE);
        g.fillRect(50, 60, 20, 120);
    }
}

Answer 1

你的代码有很多“问题”。我建议你找些教程什么的。你可以使用frame.setVisible(true)和Player的类构造函数中的内容。您是否意识到，每次创建Player对象时，所有这些都将应用于JFrame？这有必要吗？也许你应该只做一次。此外，为了根据组件的位置和大小来paint组件，您可以执行g.fillRect(50, getHeight() / 2, 20, 120);

public class Test {

    public static void main(String[] args) {
        JFrame frame = new JFrame("gEngine");
        Player playerOne = new Player();
        Player playerTwo = new Player();

        // Set the proper layout manager
        frame.setLayout(new GridLayout());

        frame.add(playerOne.getMyPanel());
        frame.add(playerTwo.getMyPanel());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setBackground(Color.BLACK);
        frame.setSize(1280, 720);
        frame.setVisible(true);
    }

    public static class Player {
        private JPanel myPanel;

        public Player() {
            this.myPanel = new MyPanel();
        }

        public JPanel getMyPanel() {
            return myPanel;
        }

    }

    static class MyPanel extends JPanel {
        @Override
        public void paintComponent(Graphics g) {
            // let the component be painted "natural"
            super.paintComponent(g);
            // Do custom painting
            g.setColor(Color.WHITE);
            g.fillRect(50, getHeight() / 2, 20, 120);
        }
    }

}

编辑（基于评论）：

背景是默认的，因为GridLayout将屏幕分割为两个面板（在画面中间）。即使框架有BLACK背景，这两个面板也覆盖了它。所以你看到的背景是来自面板，而不是框架。要更改它，您必须更改面板的背景（并使其不透明）：

static class MyPanel extends JPanel {
    public MyPanel() {
        super();
        setOpaque(true);
        setBackground(Color.BLACK);
    }

    @Override
    public void paintComponent(Graphics g) {
        // let the component be painted "natural"
        super.paintComponent(g);
        // Do custom painting
        g.setColor(Color.WHITE);
        g.fillRect(50, getHeight() / 2, 20, 120);
    }
}