Java 在对象之间切换时如何去掉矩形内的圆

我有一个组合框，在其中我可以选择绘制矩形、圆形或徒手绘制。 如果我选择画一个圆，它会画得很完美。如果我然后切换到绘制一个矩形，它会在矩形内绘制一个圆。如果我先画一个矩形，然后画一个圆，也会发生同样的情况。（见下图）

我的问题是：

如何在绘制圆和矩形之间切换，而不使圆出现在矩形内

如何在拖动鼠标时显示矩形/圆形。我的意思是，在我释放鼠标点击之前，线条如何显示

为什么徒手画画不行

这是我的testclass：

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

public class Lab6 extends JFrame implements ActionListener {
    int startX, startY, endX, endY, w, h;
    ArrayList<Shape> shapeList =  new ArrayList<Shape>();
    Container cp = getContentPane();

    private JPanel topPanel;
    private JComboBox comboBox;    
    private final String[] boxOptions = new String[] {"Rektangel", "Cirkel", "Frihand"};   


    public Lab6(String title) {
        super(title);
        this.setLayout(new BorderLayout());
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setLocationRelativeTo(null);        
        this.setSize(840, 500);    
        this.initComponents();
        this.setVisible(true);
    }


    private void initComponents() {
        topPanel = new JPanel(new GridLayout(1,2));     
        topPanel.setPreferredSize(new Dimension(0,40));

        comboBox = new JComboBox(boxOptions);
        comboBox.setSelectedIndex(0);          
        comboBox.addActionListener(this);                          

        topPanel.add(comboBox);
        this.add(topPanel, BorderLayout.PAGE_START);          
    }

    @Override
    public void paint(Graphics g) {
        for (Shape s : shapeList) {
            s.draw(g);
        }
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource().equals(comboBox)) {     
            JComboBox cb = (JComboBox)e.getSource();
            if (cb.getSelectedItem().equals("Rektangel")) {                
                cp.addMouseListener(new MouseAdapter() {            
                    @Override
                    public void mousePressed(MouseEvent e) {                   
                        startX = e.getX();     
                        startY = e.getY(); 
                    }
                    @Override
                    public void mouseReleased(MouseEvent e) {
                        endX = e.getX();
                        endY = e.getY();

                        int width = startX - endX;
                        int height = startY - endY;
                        w = Math.abs(width);
                        h = Math.abs(height);

                        Rectangle r =  new Rectangle(startX, startY, w, h);

                        shapeList.add(r);
                        repaint();
                    }
                });                  
            }
            else if (cb.getSelectedItem().equals("Cirkel")) {

                cp.addMouseListener(new MouseAdapter() {            
                    @Override
                    public void mousePressed(MouseEvent e) {                   
                        startX = e.getX();     
                        startY = e.getY(); 
                    }
                    @Override
                    public void mouseReleased(MouseEvent e) {
                        endX = e.getX();
                        endY = e.getY();

                        int width = startX - endX;
                        int height = startY - endY;
                        w = Math.abs(width);
                        h = Math.abs(height);

                        Circle c =  new Circle(startX, startY, w, h);

                        shapeList.add(c);
                        repaint();
                    }
                });   
            }
            else if (cb.getSelectedItem().equals("Frihand")) {   //I need help with this part

               cp.addMouseListener(new MouseAdapter() {            
                @Override
                public void mousePressed(MouseEvent e) {            
                    startX = e.getX();
                    startY = e.getY();
                }
                @Override
                public void mouseDragged(MouseEvent e) {

                    FreeHand fh =  new FreeHand(startX, startY, e.getX(), e.getY());

                    shapeList.add(fh);
                    repaint();
                }
            });  

            }
        }
    }

    public static void main(String args[]) {
        new Lab6("Drawing Program");
    }
}

课堂上徒手（我需要这部分的帮助）：

在课堂上：

import java.awt.Graphics;
import javax.swing.JPanel;

public abstract class Shape extends JPanel {

    private int startX, startY, width, height;    

    public Shape() {
        this(0, 0, 1, 1);
    }

    public Shape(int startX, int startY, int width, int height) {
        this.startX = startX;
        this.startY = startY;
        this.width = width;
        this.height = height;
    }

    public abstract void draw(Graphics g);

    @Override
    public int getX() {
        return startX;
    }

    @Override
    public int getY() {
        return startY;
    }

    @Override
    public int getWidth() {
        return width;
    }

    @Override
    public int getHeight() {
        return height;
    }
}

---

有很多事情正在发生

覆盖

JFrame

在执行自定义绘制之前，不调用

super.paint

每次更改形状时添加新的

MosueListener

相反，创建一个自定义组件，从类似

JPanel

的东西扩展，并覆盖它的

paintComponent

方法。使用此组件具有基本的绘图表面（控件应包含在另一个组件中）

确保在执行任何自定义绘制之前调用

super.paintComponent

，以免中断绘制链

有关详细信息，请参阅和

创建一个

鼠标侦听器

，并将其注册到面板。当用户选择不同的形状时，更改面板内的状态变量（通过setter），该变量告诉

MouseListener

当用户开始绘图时应该做什么

已更新…

创建从

JPanel

扩展的自定义类

public static class ShapePane extends JPanel {

}

重写类

paintComponent

方法

public static class ShapePane extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

}

为布局管理器提供一些大小调整提示

public static class ShapePane extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

    public Dimension getPreferredSize() {
        return new Dimension(200, 200);
    }

}

提供一种可以改变形状类型的方法…这样你就知道该画什么了

public static class ShapePane extends JPanel {

    public enum ShapeType {

        CIRCLE,
        RECTANGLE
    }

    private ShapeType currentShapeType;

    public void setCurrentShapeType(ShapeType currentShapeType) {
        this.currentShapeType = currentShapeType;
    }

    public ShapeType getCurrentShapeType() {
        return currentShapeType;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

}

向自定义类添加一个

mouseStener

，以创建所需类型的形状

public static class ShapePane extends JPanel {

    public enum ShapeType {

        CIRCLE,
        RECTANGLE
    }

    private ShapeType currentShapeType;

    public ShapePane() {
        addMouseListener(new MouseAdapter() {

            private Point clickPoint;

            @Override
            public void mousePressed(MouseEvent e) {
                clickPoint = e.getPoint();
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                Point releasePoint = e.getPoint();
                int x = Math.min(releasePoint.x, clickPoint.x);
                int y = Math.min(releasePoint.y, clickPoint.y);
                int width = Math.abs(clickPoint.x - releasePoint.x);
                int height = Math.abs(clickPoint.y - releasePoint.y);
                switch (getCurrentShapeType()) {
                    case CIRCLE:
                        // Make a circle
                        break;
                    case RECTANGLE:
                        // Make a rectangle...
                        break;
                }
                repaint();
            }

        });
    }

    public void setCurrentShapeType(ShapeType currentShapeType) {
        this.currentShapeType = currentShapeType;
    }

    public ShapeType getCurrentShapeType() {
        return currentShapeType;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

}

填空

创建另一个

JPanel

（这次只需创建一个实例），将控件添加到其中

创建

JFrame

的实例，将自定义类添加到该实例和控制面板（确保它们的布局正确，以免相互覆盖-有关详细信息，请参阅）

---

对控件使用适当的侦听器来确定用户想要绘制的形状类型，并相应地设置

currentShapeType

属性…

有许多事情正在进行

覆盖

JFrame

在执行自定义绘制之前，不调用

super.paint

每次更改形状时添加新的

MosueListener

相反，创建一个自定义组件，从类似

JPanel

的东西扩展，并覆盖它的

paintComponent

方法。使用此组件具有基本的绘图表面（控件应包含在另一个组件中）

确保在执行任何自定义绘制之前调用

super.paintComponent

，以免中断绘制链

有关详细信息，请参阅和

创建一个

鼠标侦听器

，并将其注册到面板。当用户选择不同的形状时，更改面板内的状态变量（通过setter），该变量告诉

MouseListener

当用户开始绘图时应该做什么

已更新…

创建从

JPanel

扩展的自定义类

public static class ShapePane extends JPanel {

}

重写类

paintComponent

方法

public static class ShapePane extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

}

为布局管理器提供一些大小调整提示

public static class ShapePane extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

    public Dimension getPreferredSize() {
        return new Dimension(200, 200);
    }

}

提供一种可以改变形状类型的方法…这样你就知道该画什么了

public static class ShapePane extends JPanel {

    public enum ShapeType {

        CIRCLE,
        RECTANGLE
    }

    private ShapeType currentShapeType;

    public void setCurrentShapeType(ShapeType currentShapeType) {
        this.currentShapeType = currentShapeType;
    }

    public ShapeType getCurrentShapeType() {
        return currentShapeType;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

}

向自定义类添加一个

mouseStener

，以创建所需类型的形状

public static class ShapePane extends JPanel {

    public enum ShapeType {

        CIRCLE,
        RECTANGLE
    }

    private ShapeType currentShapeType;

    public ShapePane() {
        addMouseListener(new MouseAdapter() {

            private Point clickPoint;

            @Override
            public void mousePressed(MouseEvent e) {
                clickPoint = e.getPoint();
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                Point releasePoint = e.getPoint();
                int x = Math.min(releasePoint.x, clickPoint.x);
                int y = Math.min(releasePoint.y, clickPoint.y);
                int width = Math.abs(clickPoint.x - releasePoint.x);
                int height = Math.abs(clickPoint.y - releasePoint.y);
                switch (getCurrentShapeType()) {
                    case CIRCLE:
                        // Make a circle
                        break;
                    case RECTANGLE:
                        // Make a rectangle...
                        break;
                }
                repaint();
            }

        });
    }

    public void setCurrentShapeType(ShapeType currentShapeType) {
        this.currentShapeType = currentShapeType;
    }

    public ShapeType getCurrentShapeType() {
        return currentShapeType;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

}

填空

创建另一个

JPanel

（这次只需创建一个实例），将控件添加到其中

创建

JFrame

的实例，将自定义类添加到该实例和控制面板（确保它们的布局正确，以免相互覆盖-有关详细信息，请参阅）

---

对控件使用适当的侦听器来确定用户想要绘制的形状类型，并相应地设置

currentShapeType

属性…

有许多事情正在进行

覆盖

JFrame

在执行自定义绘制之前，不调用

super.paint

每次更改形状时添加新的

MosueListener

相反，创建一个自定义组件，从类似

JPanel

的东西扩展，并覆盖它的

paintComponent

方法。使用此组件具有基本的绘图表面（控件应包含在另一个组件中）

确保在执行任何自定义绘制之前调用

super.paintComponent

，以免中断绘制链

有关详细信息，请参阅和

创建一个

鼠标侦听器

，并将其注册到面板。当用户选择不同的形状时，更改面板内的状态变量（通过setter），该变量告诉

MouseListener

当用户开始绘图时应该做什么

已更新…

创建从

JPanel

扩展的自定义类

public static class ShapePane extends JPanel {

}

重写类

paintComponent

方法

public static class ShapePane extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

}

为布局管理器提供一些大小调整提示

public static class ShapePane extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

    public Dimension getPreferredSize() {
        return new Dimension(200, 200);
    }

}

提供一种可以改变形状类型的方法…这样你就知道该画什么了

public static class ShapePane extends JPanel {

    public enum ShapeType {

        CIRCLE,
        RECTANGLE
    }

    private ShapeType currentShapeType;

    public void setCurrentShapeType(ShapeType currentShapeType) {
        this.currentShapeType = currentShapeType;
    }

    public ShapeType getCurrentShapeType() {
        return currentShapeType;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

}

添加一个