在 Java 中的 Jframe 上绘制简单的矩形 [英] drawing simple rectangles on a Jframe in java

问题描述

我像这样扩展 JFrame:

I am extending JFrame like this:

public GameFrame() {
    this.setBounds(30, 30, 500, 500);
    this.setDefaultCloseOperation(EXIT_ON_CLOSE);
    initializeSquares();
}

private void initializeSquares(){
    for(int i = 0; i < 5; i++){
        this.getContentPane().add(new Square(i*10, i*10, 100, 100));
    }
    this.setVisible(true);
}

然而，屏幕上只绘制了一个正方形，有人知道为什么吗?

However, only one square is being drawn on the screen, does anybody know why?

我的 Square 类也如下所示:

also My Square class looks like this:

private int x;
private int y;
private int width;
private int height;
public Square(int x, int y, int width, int height){
    this.x = x;
    this.y = y;
    this.width = width;
    this.height = height;
}

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawRect(x, y, width, height);
}

推荐答案

JFrame 的 contentPane 默认使用 BorderLayout.当你向它添加一个 Square 时，它​​会被默认添加 BorderLayout.CENTER 并覆盖任何以前添加的 Squares.您需要阅读所有可用于 Swing GUI 的布局管理器.

The JFrame's contentPane uses BorderLayout by default. When you add a Square to it, it gets added by default BorderLayout.CENTER and covers up any previously added Squares. You will want to read up on all the layout managers available to Swing GUI's.

例如，从这里开始:在容器内布置组件

但话虽如此，我会做不同的事情.我只会创建一个 JPanel 并使其能够绘制多个正方形.例如像这样:

But having said this, I would do things differently. I would create just one JPanel and make it able to paint multiple squares. For example something like so:

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.util.ArrayList;
import java.util.List;

import javax.swing.*;

public class GameFrame extends JFrame {
   public GameFrame() {
      super("Game Frame");
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      Squares squares = new Squares();
      getContentPane().add(squares);
      for (int i = 0; i < 15; i++) {
         squares.addSquare(i * 10, i * 10, 100, 100);
      }

      pack();
      setLocationRelativeTo(null);
      setVisible(true);

   }

   public static void main(String[] args) {
      new GameFrame();
   }

}

class Squares extends JPanel {
   private static final int PREF_W = 500;
   private static final int PREF_H = PREF_W;
   private List<Rectangle> squares = new ArrayList<Rectangle>();

   public void addSquare(int x, int y, int width, int height) {
      Rectangle rect = new Rectangle(x, y, width, height);
      squares.add(rect);
   }

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

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      Graphics2D g2 = (Graphics2D) g;
      for (Rectangle rect : squares) {
         g2.draw(rect);
      }
   }

}

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