Java 在JPanel上绘制矩形

我想在一张三角板上画一个角。我能用下面的代码画画

public class DrawingColor extends JFrame
{
    public static void main(String[] args) 
    {
        DrawingColor d = new DrawingColor();
    }

    public DrawingColor()
    {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        getContentPane().add(new MyComponent());
        setSize(400,400);
        setVisible(true);
    }

    public class MyComponent extends JComponent
    {
        @Override
        public void paint(Graphics g)
        {
            int height = 200;
            int width = 120;
            g.setColor(Color.red);
            g.drawRect(10, 10, height, width);
            g.setColor(Color.gray);
            g.fillRect(11, 11, height, width);
            g.setColor(Color.red);
            g.drawOval(250, 20, height, width);
            g.setColor(Color.magenta);
            g.fillOval(249, 19, height, width);
        }
    }
}

但是getContentPane（）.add（新的MyComponent（））； 我需要在框架中添加一个基础面板，而不是此语句。在基础面板上，我想添加MyComponent面板

  JPanel basePanel = new JPanel();
  basePanel = new MyComponent();
  getContentPane().add(basePanel);

如果我这样做，矩形就看不见了。有什么想法吗？ 我还需要在运行时更改矩形的大小。有可能吗？

1）对于Swing JComponent，您必须使用

paintComponent（）

而不是

paint（）

方法

2） 您的

JComponent

不会返回

PreferredSize

比如说

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ComponentEvent;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class CustomComponent extends JFrame {

    private static final long serialVersionUID = 1L;

    public CustomComponent() {
        setTitle("Custom Component Graphics2D");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public void display() {
        CustomComponents cc = new CustomComponents();
        /*cc.addComponentListener(new java.awt.event.ComponentAdapter() {

            @Override
            public void componentResized(ComponentEvent event) {
                setSize(Math.min(getPreferredSize().width, getWidth()),
                        Math.min(getPreferredSize().height, getHeight()));
            }
        });*/
        add(cc, BorderLayout.CENTER);

        CustomComponents cc1 = new CustomComponents();
        add(cc1, BorderLayout.EAST);

        pack();
        // enforces the minimum size of both frame and component
        setMinimumSize(getSize());
        //setMaximumSize(getMaximumSize());
        setVisible(true);

    }

    public static void main(String[] args) {
        CustomComponent main = new CustomComponent();
        main.display();
    }
}

class CustomComponents extends JComponent {

    private static final long serialVersionUID = 1L;

    @Override
    public Dimension getMinimumSize() {
        return new Dimension(100, 100);
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(400, 300);
    }

    @Override
    public Dimension getMaximumSize() {
        return new Dimension(800, 600);
    }

    @Override
    public void paintComponent(Graphics g) {
        int margin = 10;
        Dimension dim = getSize();
        super.paintComponent(g);
        g.setColor(Color.red);
        g.fillRect(margin, margin, dim.width - margin * 2, dim.height - margin * 2);
    }
}

---

我试着画一个正方形和圆形，在运行时动态地改变大小…附上完整的代码…如果有帮助的话

import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Rectangle2D;
import javax.swing.*;
import java.*;
import java.awt.Canvas;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;                    

class DisplayCanvas extends Canvas
{
    static boolean clip = false;
    static boolean clipfurther = false;
    static boolean  isReset = false, isSlider = false;
    int w, h;
    static int wi = 300, hi = 300;
    public DisplayCanvas()
    {
        //setSize(300, 300);
    setBounds(20, 40, 300, 300);
    setBackground(Color.white);
    }
    public void paint(Graphics g)
    {
        Graphics2D g2=(Graphics2D) g;
    w = getSize().width;
    h = getSize().height;

    if(clip)
    {
        // Ellipse2D e = new Ellipse2D.Float(w/4.0f,h/4.0f,w/2.0f,h/2.0f);
        Rectangle2D r = null;
        if(isSlider)
        {
            r = new Rectangle2D.Float((w)/(4.0f), (h)/(4.0f), wi/2.0f, hi/2.0f);
        //     isSlider=false;
        }
        else
        r = new Rectangle2D.Float(w/4.0f, h/4.0f, wi/2.0f, hi/2.0f);
            //g2.setClip(e);

        System.out.println("Width : "+ wi +" Height : "+ hi);
        g2.setClip(r);
        System.out.println(g2.getClipBounds());

        if(shape.selectedcolor == "red")
        {
            g2.setColor(Color.red);
        }
        else if(shape.selectedcolor == "blue")
        {
            g2.setColor(Color.BLUE);
        }
        else if(shape.selectedcolor == "yellow")
        {
            g2.setColor(Color.yellow);
        }

        //g2.setColor(Color.RED);
        g2.fillRect(0, 0, w, h);
        }
    else if(clipfurther)
    {
        //Rectangle r = new Rectangle(w/4, h/4, w/4, h/4);
        Ellipse2D r = new Ellipse2D.Float(w/4.0f, h/4.0f, wi/2.0f, hi/2.0f);
        g2.clip(r);
        //g2.setColor(Color.green);
        //g2.setColor(Color.getColor(shape.selectedcolor));

        if(shape.selectedcolor == "red")
        {
            g2.setColor(Color.red);
        }
        else if(shape.selectedcolor == "blue")
        {
        g2.setColor(Color.BLUE);
        }
        else if(shape.selectedcolor == "yellow")
        {
        g2.setColor(Color.yellow);
        }

        g2.fillRect(0, 0, w, h);
        }
    }   
}

class RadioListener implements ActionListener
{
    public void actionPerformed(ActionEvent e)
    {
        if(e.getSource() == shape.circle)
        {
        shape.selectedcolor = shape.selectedcolor_reset;
        System.out.println("Inside circle "+            shape.selectedcolor_reset);
        System.out.println("2222222222");
        DisplayCanvas.clip = true;
        DisplayCanvas.clipfurther = false;
        shape.canvas.repaint();
    }
    if (e.getSource() == shape.square)
    {
        shape.selectedcolor = shape.selectedcolor_reset;
        System.out.println("333333333333333");
        DisplayCanvas.clip = false;
        DisplayCanvas.clipfurther = true;
        shape.canvas.repaint();
    }                  
    }
}

class shape extends JFrame implements ActionListener
{
    static String fname;
    static JPanel panel, draw;
    static Container contentpane, draw_pane;
    static JFrame frame;
    static JLayeredPane layer, draw_layer;
    static JTextField user;
    static JButton reset, cancel;

    static JLabel file1, file2;
    static JTextField text1;
    static JRadioButton circle, square;
    static JInternalFrame iframe, errmessage;
    static JComboBox colors;
    static JEditorPane sqc;
    static JScrollPane scroller;
    static JSlider slider;
    String colors_array[]={"...", "red", "blue", "yellow"};
    static DisplayCanvas canvas;
    static String selectedcolor, selectedcolor_reset;

    shape()
    {
        canvas=new DisplayCanvas();

    panel= new JPanel();
    panel.setBounds(20,20,250,140);
    //panel.setLayout(new FlowLayout(10, 10, 10));
    panel.setLayout(null);
    contentpane = getContentPane();
    contentpane.add(canvas);
    //draw_pane=getContentPane();

    layer = new JLayeredPane();
    layer.setBounds(50,245,300,205);
    layer.setForeground(Color.blue);

    draw_layer = new JLayeredPane();
    draw_layer.setBounds(200, 200, 80, 30);
    draw_layer.setForeground(Color.BLACK);

    draw = new JPanel();
    draw.setBounds(20, 20, 250, 300);
    draw.setLayout(null);

    reset = new JButton("RESET");
    reset.setBounds(360, 60, 100, 25);

    circle = new JRadioButton("Square");
    circle.setBounds(400, 100, 100, 40);
    circle.setActionCommand("encryption");

    square = new JRadioButton("Circle");
    square.setBounds(330,100, 60, 40);
    square.setActionCommand("decryption");

    colors = new JComboBox(colors_array);
    colors.setBounds(405, 140, 80, 30);
    colors.setVisible(true);

    file1 = new JLabel(" Select Color :");
    file1.setBounds(320, 130, 150, 50);
    //defining the Button Group for the Radio Buttons

    ButtonGroup group = new ButtonGroup();
    group.add(circle);
    group.add(square);

    cancel = new JButton("Exit");
    cancel.setBounds(365, 250, 85, 25);

    file2 = new JLabel("SIZE :");
    file2.setBounds(336, 180, 150, 50);
    setslider(0, 100, 100, 25, 5);
    slider.setBounds(386, 190, 100, 50);

        slider.setVisible(true);

    panel.add(file2);
    panel.add(layer);
        panel.add(circle);
    panel.add(square);
    panel.add(colors);
    panel.add(slider);
    panel.add(file1);
    panel.add(reset);
    panel.add(cancel);
    //panel.add(new CircleDraw());

    //draw.add(draw_layer);
    // draw_pane.add(draw);
    contentpane.add(panel);
    //   contentpane.add(draw);
    //  contentpane.add(scroller);
    RadioListener radio = new RadioListener();
    circle.addActionListener(radio);
    square.addActionListener(radio);
    reset.addActionListener(this);
    cancel.addActionListener(this);

    colors.addActionListener(new ActionListener()
    {
        public void actionPerformed(ActionEvent ae)
        {                           
            JComboBox cb = (JComboBox)ae.getSource();
        selectedcolor = (String)cb.getSelectedItem();
        System.out.println(selectedcolor);
        selectedcolor_reset = selectedcolor;
        System.out.println("SELECTED "+ cb.getSelectedIndex());
        canvas.repaint();
        }
        });

    addWindowListener(new WindowAdapter()
    {
        public void windowClosing(WindowEvent e)
        {
            System.exit(0);
        }
    });
    }

    public void actionPerformed(ActionEvent e) 
    {
        if(e.getSource()== cancel)
    {
        System.exit(0);
    }
    if (e.getSource() == reset)
    {
        System.out.println("111111111");
        DisplayCanvas.clip = true;
        DisplayCanvas.clipfurther = false;
        DisplayCanvas.isReset = true;
        shape.selectedcolor = "...";
        System.out.println(" PREVIOUS " + selectedcolor_reset);
        DisplayCanvas.hi = DisplayCanvas.wi = 300;
        canvas.repaint();
    }
    }
    public class SliderListener implements ChangeListener 
    {
        public SliderListener() 
        {
    }
    public void stateChanged(ChangeEvent e) 
        {
        JSlider slider = (JSlider)e.getSource();
        System.out.println(slider.getValue());
        DisplayCanvas.wi = slider.getValue() * 3;
        DisplayCanvas.hi = DisplayCanvas.wi;
        DisplayCanvas.isSlider = true;
        canvas.repaint();
    }
    }
    public void setslider(int min,int max,int init,int mjrtk,int mintk)
    {
        slider = new JSlider(JSlider.HORIZONTAL, min, max, init);
    slider.setPaintTicks(true);
    slider.setMajorTickSpacing(mjrtk);
    slider.setMinorTickSpacing(mintk);
    slider.setPaintLabels(true);
    slider.addChangeListener((ChangeListener) new SliderListener());
    }
}

public class display 
{
    static JFrame frame;
    /**
      * @param args the command line arguments
      */
    public static void main(String[] args) 
    {
        // TODO code application logic here
    frame=new shape();

    frame.setBounds(380, 200, 500, 400);
    frame.setTitle("SHAPE AND COLOR");
    frame.setVisible(true);

    }
}

---

由于要在运行时更改矩形的尺寸，请尝试以下代码：

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

public class RectangleTest extends JFrame {

    private int x;
    private int y;
    private static JButton buttonFullSize;
    private static JButton buttonHalfSize;

    public RectangleTest() {
        x = 0;
        y = 0;

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final JPanel basePanel = new JPanel();
        basePanel.setLayout(new BorderLayout());

        final MyComponent component = new MyComponent(400, 400);
        component.setOriginAndSize(0, 0, 100, 100);
        buttonFullSize = new JButton("DRAW FULL SIZE");
        buttonFullSize.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent ae) {
                component.setOriginAndSize(x++, y++,
                    (basePanel.getHeight() / 4), (basePanel.getWidth() / 4));            
            }
        });

        buttonHalfSize = new JButton("DRAW HALF SIZE");
        buttonHalfSize.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent ae) {
                component.setOriginAndSize(x++, y++,
                    (basePanel.getHeight() / 8), (basePanel.getWidth() / 8));
            }
        });

        basePanel.add(buttonHalfSize, BorderLayout.PAGE_START);
        basePanel.add(component, BorderLayout.CENTER);
        basePanel.add(buttonFullSize, BorderLayout.PAGE_END);

        setContentPane(basePanel);
        pack();
        setVisible(true);               
    }

    public static void main(String... args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new RectangleTest();                
            }
        });
    }
}

class MyComponent extends JComponent {

    private int x;
    private int y;
    private int width;
    private int height;
    private int compWidth;
    private int compHeight;

    MyComponent(int w, int h) {
        this.compWidth = w;
        this.compHeight = h;
    }

    public void setOriginAndSize(int x, int y, int w, int h) {
        this.x = x;
        this.y = y;
        this.width = w;
        this.height = h;
        repaint();
    }

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

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(getBackground());
        g.fillRect(x, y, width, height);
        g.setColor(Color.RED);
        g.drawOval(x, y, width, height);
        g.setColor(Color.MAGENTA);
        g.fillOval(x, y, width, height);
    }
}

---

@mKorbel：这段代码运行得很好，但是已经有一个jpanel，它被添加到jframe中，在jpanel上面我想添加CustomComponents。JPanel面板=新的JPanel（）；框架。添加（面板）；panel.add（新的CustomComponents（））；对于此代码，我无法看到矩形。@Sathish请阅读我关于使用的LayoutManager的回答，请阅读链接的BorderLayout教程请缩进您的代码。+1，有趣的问题，帮助我了解了一些事情：-）我尝试格式化代码，但他不接受，天知道为什么，尽管它工作得很好。-1用于使用Canvas类进行自定义绘制。Swing应用程序应该在JComponent或JPanel上进行自定义绘制，并且应该重写paintComponent（）方法。