图像显示

1 使用Graphics.drawImage(Image img, int x, int y, ImageObserver observer)
方法显示图像。

2 使用Component.getToolkit.getImage(String path)语句获得Image实例对象。

例：
package drawimage;

import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class DrawImage extends Frame
{
    private static final long serialVersionUID = 1L;
 
    public DrawImage()
 {
   this.addWindowListener(new WindowAdapter()
      {
       public void windowClosing(WindowEvent e)
       {
        dispose();
        System.exit(0);
       }
   
       });
 }
 public static void main(String[] args)
 {
  System.out.println("Starting DrawImage.");
  DrawImage mainFrame = new DrawImage();
  Image img = mainFrame.getToolkit().getImage("love.jpg");
  
  mainFrame.setSize(400,400);
  mainFrame.setTitle("DrawImage");
  mainFrame.setVisible(true);
  Graphics g = mainFrame.getGraphics();
  while(!g.drawImage(img,150,150,mainFrame));
  
 

 }

}

图像重画

package drawimage;

import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class DrawImage extends Frame
{
 Image img = getToolkit().getImage("love.jpg");
    private static final long serialVersionUID = 1L;
 public void paint(Graphics g)
 {
  g.drawImage(img,0,0,this);
 }
    public DrawImage()
 {
   this.addWindowListener(new WindowAdapter()
      {
       public void windowClosing(WindowEvent e)
       {
        dispose();
        System.exit(0);
       }
   
       });
 }
 public static void main(String[] args)
 {
  System.out.println("Starting DrawImage.");
  DrawImage mainFrame = new DrawImage();
  
  mainFrame.setSize(400,400);
  mainFrame.setTitle("DrawImage");
  mainFrame.setVisible(true);
  /*Graphics g = mainFrame.getGraphics();
  while(!g.drawImage(img,150,150,mainFrame));
  */
 

 }

}

双缓冲技术：

1  Component.createImage方法创建内存Image对象
2  在Image对象上进行绘制的结果就成了一幅图像
3  在Image对象上执行与组件表面同样的绘制，Image
     对象中的图像就是组件表面内容的复制，当组件重画    时，只需要将内存中的Image对象在组件上画出；

package drawline;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
//import java.util.Enumeration;
import java.util.Vector;

public class DrawLine1 extends Frame
{
 int orgX;
 int orgY;
 int endX;
 int endY;
 Image oimg = null;
 Graphics og = null;
 Vector<MyLine> vLines = new Vector<MyLine>();
 
 public void paint(Graphics g)
 {
  if(oimg != null)
  {
    g.drawImage(oimg,0,0,this);
  }
  /*g.setColor(Color.RED);
  g.setFont(new Font(null,Font.ITALIC|Font.BOLD,30));
  Enumeration<MyLine> e = vLines.elements();
  while(e.hasMoreElements())
  {
   MyLine line = (MyLine)e.nextElement();
      line.drawMe(g);
  }*/
  //g.drawLine(orgX, orgY, endX, endY);
 }
 private static final long serialVersionUID = 9004940250333651314L;

 public DrawLine1()
 {
  setSize(400,400);
  setTitle("Drawline");
  setVisible(true);
  
  Dimension d = getSize();
  oimg = createImage(d.width,d.height);
  og = oimg.getGraphics();
  
     addWindowListener(new WindowAdapter()
     {
      public void windowClosing(WindowEvent e) {
       dispose();
       System.exit(0);
      }
   
     });
  
  this.addMouseListener(new MouseAdapter()
  {
      
      
      public void mousePressed(MouseEvent e)
      {
       orgX = e.getX();
       orgY = e.getY();
       
      }
      public void mouseReleased(MouseEvent e)
      {
       endX = e.getX();
       endY = e.getY();
       Graphics g = getGraphics();
       g.setColor(Color.RED);
       g.setFont(new Font(null,Font.ITALIC|Font.BOLD,30));
       g.drawString(orgX + "," + orgY,orgX,orgY);
       g.drawString(e.getX() + "," + e.getY(), e.getX(),e.getY());
       g.drawLine(orgX, orgY, e.getX(),e.getY());
       
       og.setColor(Color.RED);
       og.setFont(new Font(null,Font.ITALIC|Font.BOLD,30));
       og.drawString(orgX + "," + orgY,orgX,orgY);
       og.drawString(e.getX() + "," + e.getY(), e.getX(),e.getY());
       og.drawLine(orgX, orgY, e.getX(),e.getY());
       /*vLines.add(new MyLine(orgX,orgY,endX,endY));
       repaint();*/
      }//为什么用getGraphics().setColor(Color.RED)是不用导java.awt.Graphics包
      //Enumeration<MyLine>???????????????????????????
      
      
     });
 }

 public static void main( String[] args) {
  System.out.println("String DrawLine");
   new DrawLine1();
  
  
  
 }
}

//构建主框架对象时是先调用paint（）还是构造函数