1. AWT画图  Graphics类  提供绘制简单图形的方法

更新图片时用到 repaint , update , 程序不应该主动调用paint和update， 这两个方法都应该是由AWT系统负责调用，用户重写paint 即可。

示例：

public class Main {private final String RECT_SHAPE = "rect";private final String OVAL_SHAPE = "oval";private Frame f = new Frame();private Button rect = new Button("Rect");private Button oval = new Button("Oval");private String shape = "";private MyCanvas drawArea = new MyCanvas();void init(){Panel p = new Panel();p.add(rect);p.add(oval);rect.addActionListener(new ActionListener() {          @Overridepublic void actionPerformed(ActionEvent e) {// TODO Auto-generated method stubshape = RECT_SHAPE;drawArea.repaint();  //重画， 会调用paint方法。。。}});oval.addActionListener(new ActionListener() {            @Overridepublic void actionPerformed(ActionEvent e) {// TODO Auto-generated method stubshape = OVAL_SHAPE;drawArea.repaint();}});f.addWindowListener(new WindowAdapter() {public void windowClosing(WindowEvent e){System.exit(0);}});drawArea.setPreferredSize(new Dimension(250, 180));f.add(drawArea);f.add(p, BorderLayout.SOUTH);f.pack();f.setVisible(true);}public static void main(String[] args) {new Main().init();}class MyCanvas extends Canvas  // 画布{public void paint(Graphics g)  //重写paint方法{Random rand = new Random();if(shape.equals(RECT_SHAPE)){g.setColor(new Color(220, 100, 80));g.drawRect(rand.nextInt(200), rand.nextInt(120), 40, 60);}if(shape.equals(OVAL_SHAPE)){g.setColor(new Color(80, 100, 200));g.fillOval(rand.nextInt(200), rand.nextInt(120), 50, 40);}}}
}

2. 使用image类 BufferedImage 类处理位图

画板：

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.MenuItem;
import java.awt.PopupMenu;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.event.MouseMotionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.image.BufferedImage;public class HandDraw {/*** @param args*///画区大小private final int AREA_WIDTH = 500;private final int AREA_HEIGHT = 400;//鼠标坐标private int preX = -1;private int preY = -1;//右键惨淡PopupMenu pop = new PopupMenu();MenuItem redItem = new MenuItem("Red");MenuItem greenItem = new MenuItem("Green");MenuItem blueItem = new MenuItem("Blue");//Bufferedimage 对象BufferedImage image = new BufferedImage(AREA_WIDTH, AREA_HEIGHT, BufferedImage.TYPE_INT_RGB);Graphics g = image.getGraphics();private Frame f= new Frame("HandDraw");private String shape = "";private Color foreColor = new Color(255, 0, 0);private DrawCanvas drawArea = new DrawCanvas();public void init(){ActionListener menuListener = new ActionListener() {           @Overridepublic void actionPerformed(ActionEvent e) {// TODO Auto-generated method stubif( e.getActionCommand().equals("Green") ){foreColor = new Color(0, 255, 0);System.out.println("Green");}else if( e.getActionCommand().equals("Red") ){foreColor = new Color(255, 0, 0);System.out.println("Red");}else if( e.getActionCommand().equals("Blue") ){foreColor = new Color(0, 0, 255);System.out.println("Blue");}          }};redItem.addActionListener(menuListener);greenItem.addActionListener(menuListener);blueItem.addActionListener(menuListener);pop.add(redItem);pop.add(greenItem);pop.add(blueItem);drawArea.add(pop);drawArea.addMouseListener(new MouseAdapter() {public void mouseReleased(MouseEvent e){if(e.isPopupTrigger()){pop.show(drawArea, e.getX(), e.getY());}preX = -1;preY = -1;}});g.fillRect(0, 0, AREA_WIDTH, AREA_HEIGHT);drawArea.setPreferredSize(new  Dimension(AREA_WIDTH, AREA_HEIGHT));drawArea.addMouseMotionListener(new MouseMotionAdapter() {public void mouseDragged(MouseEvent e) {if( preX > 0 && preY > 0 ){g.setColor(foreColor);g.drawLine(preX, preY, e.getX(), e.getY());                  }preX = e.getX();preY = e.getY();drawArea.repaint();}});f.addWindowListener(new WindowAdapter() {public void windowClosing(WindowEvent w){System.exit(0);}});f.add(drawArea);f.pack();f.setVisible(true);}public static void main(String[] args) {// TODO Auto-generated method stubnew HandDraw().init();}class DrawCanvas extends Canvas{public void paint(Graphics g){g.drawImage(image, 0, 0, null);}}}

3. 使用ImageIO  输入 输出位图

ImageIO有静态方法  getReaderFormatNames() 等获取 支持的读入写入的图片格式。

public class Main {private final int WIDTH = 800;private final int HEIGHT = 600;BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB );Graphics g= image.getGraphics();public void zoom() throws IOException{Image srcImage = ImageIO.read(new File("/home/test/test.png")); //读取图片文件g.drawImage(srcImage, 0, 0, WIDTH, HEIGHT, null);  //将原始图片 按固定大小绘制到image中ImageIO.write(image, "jpeg", new File("/home/test/testCopy.jpg"));  //写入磁盘}public static void main(String[] args) throws IOException {// TODO Auto-generated method stubnew Main().zoom();}
}