imageapplettracebyio.java

《Java实例入门》所有实例的源代码。所有的源文件都是.java文件

/**
 * Title:
 * Description:
 * Copyright:    Copyright (c) 2001
 * Company:
 * @author
 * @version 1.0
 */

import java.applet.Applet;
import java.awt.*;
import java.awt.image.*;

public class imageAppletTraceByIO extends Applet implements ImageObserver
{

    Image img = null;    
    int Mx = 0;
    int My = 0;							//鼠标按下的位置
    int width = 0;
    int height = 0;						//选定区域的宽和高

    public void init()
    {
        img = getImage(getCodeBase(), "fun.jpg");		//下载图像        
        resize(200,200) ;
        width = 100;
        height = 100;
    }

    public boolean mouseDown(Event event, int i, int j)
    {
        Mx = i;
        My = j;							//记录鼠标按下的位置
        repaint();
        return true;
    }

    public void paint(Graphics g)
    {
    	//由于类component实现了接口ImageObserver，所以方法drawImage
	//中的ImageObserver型参数为this
        g.drawImage(img, 0, 30, this);				//显示原始图像
        g.drawString("This is the original picture", 10,20);
        if(Mx > 0)
        {
            int i = Math.max(0, Mx - width / 2);
            int j = Math.max(0, My - height / 2);		//计算左上角图标
            g.copyArea(i, j, width, height, 280, 0);
            g.drawString("Using copyArea method", 280, 120);
            g.drawString("Using clipRect method", 430, 120);	//将图像的一部分拷贝
            g.clipRect(430 + i, j, width, height);		//设置裁减区域
            g.drawImage(img, 430, 0, this);
        }
    }
    //重载imageUpdate()方法以实现对图形下载情况的跟踪
	public boolean imageUpdate(Image img, int infoflags, int x, int y, int width, int height){
		if((infoflags & WIDTH)==0)					//图像宽度是否有效
			System.out.println("width="+width+"(not available)");
		else
			System.out.println("width="+width+"(available)");
		if((infoflags & HEIGHT)==0)					//图像高度是否有效
			System.out.println("height="+height+"(not available)");
		else
			System.out.println("height="+height+"(available)");
		if ((infoflags & ALLBITS)==0){					//图像是否被完全下载
			System.out.println("Image not loaded");
			return true;
		}
		else{
			System.out.println("Image is completely loaded");
			repaint();
			return false;								//不需要继续跟踪
		}
	}    
}