java awt唯一的repaint（），update（），paint（）的问题

Question

这是具有给定要求的练习。

• 仅awt，因此没有FX或Swing
• 2类首先是绘制2个按钮的主，然后将
• 随机绘制一个矩形或圆形绘制，如果您按Draw Button，则
• 用帆布部分按下另一个类，我们将对象
• 从对象中清除了 画布如果您按“清除”按钮，
• 两个类都需要扩展框架，

我大部分都解决了它，但是我现在有一个问题 清除按钮也可以工作绘制按钮，但问题是我不能接一个地绘制多个对象。 如果我绘制一个对象，然后另一个对象，则第一个由于repaint（）方法而消失。 我的两个想法是Override Update（）或将阵列列表中的图形安全性，或者

public class Main extends Frame implements ActionListener {
CanvasPart c;

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

}

public Main() {
    super();
    setSize and Title....

    Button draw = new Button("draw");
    Button clear = new Button("clear");
    draw.addActionListener(this);
    clear.addActionListener(this);

    **new Panel and adding buttons**
    c = new CanvasPart();


}//Main

@Override
public void actionPerformed(ActionEvent act) {
    try {
        if(act.getActionCommand().equals("clear")) {
            c.clear();
        }

        if(act.getActionCommand().equals("draw")) {
            c.repaint();
        }
    }catch(Exception exep) {
        exep.printStackTrace();
    }

}

public class CanvasPart extends Frame{
Canvas canvas = new Canvas();
public DrawFrame() {
    **set size location and name ....**
}

@Override
public void paint(Graphics gra) {
    super.paint(gra);
    Graphics2D gra2D = (Graphics2D) gra;
**pick random rectangle or circle......
and paint them on canvas **
}


    public void clear(){
    repaint();
}

我希望问题以某种方式可以理解。因为很难找到解决方案或想法，这很难。

Answer 1

将您绘制的每种形状保持在某种list中，这样，您可以继续将形状添加到列表中，然后继续绘制列表中的内容。

import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagLayout;
import java.awt.Panel;
import java.awt.Rectangle;
import java.awt.Shape;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Ellipse2D;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public final class Main {
    public static void main(String[] args) {
        new Main();
    }

    public Main() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                Frame frame = new Frame();
                frame.add(new MainPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class MainPane extends Panel {

        private DrawingPane drawingPane;

        public MainPane() {
            setLayout(new BorderLayout());
            Button rectangleButton = new Button("Rectangle");
            Button circleButton = new Button("Circle");
            Button clearButton = new Button("Clear");
            Panel buttonPane = new Panel(new GridBagLayout());
            buttonPane.add(rectangleButton);
            buttonPane.add(circleButton);
            buttonPane.add(clearButton);

            rectangleButton.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    drawingPane.addRectangle();
                }
            });
            circleButton.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    drawingPane.addCircle();
                }
            });
            clearButton.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    drawingPane.clear();
                }
            });

            add(buttonPane, BorderLayout.NORTH);

            drawingPane = new DrawingPane();
            add(drawingPane);
        }

    }

    public class DrawingPane extends Panel {

        private List<Shape> shapes = new ArrayList<>();
        private Random rnd = new Random();

        public DrawingPane() {
        }

        public void addRectangle() {
            int width = rnd.nextInt(getWidth() / 2) + 5;
            int height = rnd.nextInt(getWidth() / 2) + 5;
            int x = rnd.nextInt(getWidth() - width);
            int y = rnd.nextInt(getHeight() - height);
            shapes.add(new Rectangle(x, y, width, height));
            repaint();
        }

        public void addCircle() {
            int width = rnd.nextInt(getWidth() / 2) + 5;
            int height = rnd.nextInt(getWidth() / 2) + 5;
            int x = rnd.nextInt(getWidth() - width);
            int y = rnd.nextInt(getHeight() - height);
            shapes.add(new Ellipse2D.Double(x, y, width, height));
            repaint();
        }

        public void clear() {
            shapes.clear();
            repaint();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        @Override
        public void paint(Graphics g) {
            super.paint(g);
            Graphics2D g2d = (Graphics2D) g.create();
            for (Shape shape : shapes) {
                g2d.draw(shape);
            }
        }

    }
}

nb：我知道，它不使用多个frame s，那是因为这不是一个好主意做一些工作