java - JPanel/JPanel 上的随机矩形

Question

我需要创建一个在 JFrame 或 JPanel 上显示多个矩形的程序。这是我到目前为止提出的代码:

import javax.swing.*;
import java.util.Random;
import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;


public class RandomRectangles extends JFrame {
private static final int FRAME_HEIGHT = 300;
private static final int FRAME_WIDTH = 250;

private JButton fewer;
private JButton more;
private Random generator = new Random();
private int count;
private JPanel display;
private JPanel panel;

public RandomRectangles()
{
    count =  generator.nextInt(100);

    setSize(FRAME_WIDTH, FRAME_HEIGHT);
    this.setTitle("Random Rectangles");

    display = new JPanel(new BorderLayout());
    setLayout(new BorderLayout());
    //display = new JPanel(new GridLayout(2,2));
    JPanel buttons = new JPanel();

    fewer = new JButton("Fewer");
    more = new JButton("More");

    buttons.add(fewer);
    buttons.add(more);

    class  fewerNum implements ActionListener
    {
        public void actionPerformed(ActionEvent event)
        {
            count = count / 2;
        }
    }

    ActionListener listener = new fewerNum();
    fewer.addActionListener(listener);

    class  moreNum implements ActionListener
    {
        public void actionPerformed(ActionEvent event)
        {
            count = count * 2;
        }
    }

    ActionListener listener2 = new moreNum();
    more.addActionListener(listener2);

    for (int i = 0; i <= count; i++)
    {
     // display.add(new RectangleComponent());
       add(new RectangleComponent());
    }


    //add(display, BorderLayout.CENTER);
    add(buttons, BorderLayout.SOUTH);
}

}

上面的代码可以编译，但是有几个缺陷。这些按钮在单击时不执行任何操作，而是将 RectangleComponent 对象添加到框架或面板。我还创建了一个单独的 RectangleComponent 类来绘制矩形对象

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.util.Random;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class RectangleComponent extends JComponent{

private Random generator = new Random();
private int xLeft;
private int yTop;

public RectangleComponent()
{
    xLeft = generator.nextInt(100);
    yTop = generator.nextInt(100);
}

public void paintComponent(Graphics g)
{
    Graphics2D g2 = (Graphics2D) g;
    Rectangle rec = new Rectangle(xLeft, yTop, 20, 40);
    int amount = generator.nextInt(100);
    g2.draw(rec);
}

}

我要做的是:编写一个程序，在随机位置显示多个矩形。提供生成更少或更多随机矩形的按钮“更少”和“更多”。每次用户点击“更少”时，计数应该减半。每次用户点击“更多”时，计数都应该加倍。

Answer 1

你的 [更多] 和 [更少] 按钮只是设置矩形的数量，而不是添加或删除它们。你必须以某种方式重新创建它们。

如果您只想显示矩形，则不需要创建 RectangleComponent - 您可以覆盖 JFrame 的绘制调用 super.paint，然后放置和绘制矩形。在这种情况下，您必须在所有 ActionListener 的 jframe 上添加 repaint()。

编辑:更好的想法是添加一个 jpanel 并仅在此面板上绘制矩形，否则矩形将覆盖按钮并在单击按钮后“消失”，查看此 simple demo