Java AWT |帆布类

Canvas 类是Java AWT 的一部分。画布是一个空白的矩形区域，用户可以在其中绘制或捕获用户的输入。 Canvas 类继承了 Component 类。
Canvas 类的构造函数是：

1. Canvas() ：创建一个新的空白画布。
2. Canvas(GraphicsConfiguration c) ：创建具有指定图形配置的新画布。

Canvas类中常用的方法

Method	Explanation
addNotify()	Creates the peer of the canvas.
createBufferStrategy(int n)	Creates a new strategy for multi-buffering on this component.
createBufferStrategy(int n, BufferCapabilities c)	Creates a new strategy for multi-buffering on this component with the required buffer capabilities
getBufferStrategy()	Returns the BufferStrategy used by this component.
paint(Graphics g)	paints this component.
update(Graphics g)	updates this canvas.

下面的程序说明了 Canvas 类的使用：

• 程序 1：创建画布并绘制画布。
  

Java

// Java Program to create a to create
// a canvas and paint the canvas
import java.awt.*;
import javax.swing.*;
class canvas extends JFrame {
 
    // constructor
    canvas()
    {
        super("canvas");
 
        // create a empty canvas
        Canvas c = new Canvas() {
 
            // paint the canvas
            public void paint(Graphics g)
            {
                // set color to red
                g.setColor(Color.red);
 
                // set Font
                g.setFont(new Font("Bold", 1, 20));
 
                // draw a string
                g.drawString("This is a canvas", 100, 100);
            }
        };
 
        // set background
        c.setBackground(Color.black);
 
        add(c);
        setSize(400, 300);
        show();
    }
 
    // Main Method
    public static void main(String args[])
    {
        canvas c = new canvas();
    }
}

• 输出：
  

• 程序2：创建一个画布并在画布上添加鼠标监听器（在画布上单击或拖动鼠标的点会出现一个半径为5的圆）。
  

Java

// Java Program to create a
// canvas and mouse listener to the
// canvas ( a circle of radius 5 will appear
// at the points where mouse are clicked or
//  dragged on the canvas)
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
 
class canvas extends JFrame implements MouseListener, MouseMotionListener {
 
    // create a canvas
    Canvas c;
 
    // constructor
    canvas()
    {
        super("canvas");
 
        // create a empty canvas
        c = new Canvas() {
            public void paint(Graphics g)
            {
            }
        };
 
        // set background
        c.setBackground(Color.black);
 
        // add mouse listener
        c.addMouseListener(this);
        c.addMouseMotionListener(this);
 
        add(c);
        setSize(400, 300);
        show();
    }
 
    // mouse listener  and mouse motion listener methods
    public void mouseClicked(MouseEvent e)
    {
        Graphics g = c.getGraphics();
 
        g.setColor(Color.red);
 
        // get X and y position
        int x, y;
        x = e.getX();
        y = e.getY();
 
        // draw a Oval at the point
        // where mouse is moved
        g.fillOval(x, y, 5, 5);
    }
 
    public void mouseMoved(MouseEvent e)
    {
    }
 
    public void mouseDragged(MouseEvent e)
    {
        Graphics g = c.getGraphics();
 
        g.setColor(Color.red);
 
        // get X and y position
        int x, y;
        x = e.getX();
        y = e.getY();
 
        // draw a Oval at the point where mouse is moved
        g.fillOval(x, y, 5, 5);
    }
 
    public void mouseExited(MouseEvent e)
    {
    }
 
    public void mouseEntered(MouseEvent e)
    {
    }
 
    public void mouseReleased(MouseEvent e)
    {
    }
 
    public void mousePressed(MouseEvent e)
    {
    }
    // main class
    public static void main(String args[])
    {
        canvas c = new canvas();
    }
}

• 输出：
  

参考： https: Java/awt/Canvas.html