keyto8_3.java

Java程序设计第八章的课后练习题目的答案 欢迎大家来参考

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

public class KeyTo8_3 extends JApplet implements Runnable{
	int Rectangle1_x;
	int Rectangle1_y;
	int dx;
	int dy;
	int Rectangle2_x;;
	int Rectangle2_y;;
	int xPosition;
	int yPosition;
	int wordSize=20;
	int Direct_x;
	int Direct_y;
	int xLeft;
	int xRight;
	int yTop;
	int yBottom;
	int xFlag;
	int yFlag;
	double Random;
	boolean st;
	String str="Java Programming";
	Font wordFont;
	Thread TextThread;
	Image OffScreen;
	Graphics drawOffScreen;
	public void init(){
		wordFont=new Font("TimesRoman",Font.BOLD,wordSize);
		Rectangle1_x=getSize().width;
	    Rectangle1_y=getSize().height;
	    dx=20;
	    dy=20;
	    Rectangle2_x=Rectangle1_x-2*dx;
	    Rectangle2_y=Rectangle1_y-2*dy;
	    xPosition=Rectangle1_x/2;
	    yPosition=Rectangle1_y/2;

	    
	    xLeft=dx;
	    xRight=Rectangle1_x-dx-str.length();
	    yTop=dy+8;
	    yBottom=Rectangle1_y-dx;
	    xFlag=1;
	    yFlag=1;
	    Random=Math.random()*Math.PI*2;
	    Direct_x=xLeft+(int)(Math.cos(Random)*(xRight-xLeft));
	    Direct_y=yTop+(int)(Math.sin(Random)*(yBottom-yTop));
	    st=true;
	    OffScreen=createImage(Rectangle1_x,Rectangle1_y);
	    drawOffScreen=OffScreen.getGraphics();
	}
	
	public void start(){
		if(Direct_x>Direct_y){
			Direct_x=Direct_x/Direct_y;
			Direct_y=1;
		}
		else{
			Direct_y=Direct_y/Direct_x;
			Direct_x=1;
		}
		if(TextThread==null){
			TextThread=new Thread(this);
			TextThread.start();
		}
	}
	public void stop(){
		if(TextThread!=null){
			TextThread.stop();
			TextThread=null;
		}
	}
	public void run(){

		while(true){
			xPosition+=Direct_x*xFlag;
			yPosition+=Direct_y*yFlag;
			if(xPosition<=xLeft){
			
				xFlag=1;
				if(Direct_x<0)
				   Direct_x*=-1;
			}
			if(xPosition>=xRight-str.length()*wordSize/2-2)
				xFlag=-1;	
			if(yPosition<=yTop+wordSize/2){
			
				   yFlag=1;
				   if(Direct_y<0)
				      Direct_y*=-1;
			}
			if(yPosition>=yBottom-wordSize/2+6)
				   yFlag=-1;
			
			
			
			
			if(xPosition<xLeft)
			   xPosition=xLeft;
			if(xPosition>xRight-str.length()*wordSize/2-2)
			   xPosition=xRight-str.length()*wordSize/2-2;
			if(yPosition<yTop+wordSize/2)
			   yPosition=yTop+wordSize/2;
			if(yPosition>yBottom-wordSize/2+6)
			   yPosition=yBottom-wordSize/2+6;
			   
			repaint();
			try{
				Thread.sleep(20);
			}catch(InterruptedException e){}
		}
	}

	public void paint(Graphics g){
		if(st==true){
		  drawOffScreen.setColor(Color.blue);
		  drawOffScreen.fillRect(0,0,Rectangle1_x,Rectangle1_y);
		}
        
    	drawOffScreen.setColor(Color.black);
		drawOffScreen.fillRect(dx,dy,Rectangle1_x-2*dx,Rectangle1_y-2*dy);
		drawOffScreen.setColor(Color.red);
		drawOffScreen.setFont(wordFont);
		drawOffScreen.drawString(str,xPosition,yPosition);
		g.drawImage(OffScreen,0,0,this);
		st=false;
	}
	public void update(Graphics g){
		paint(g);
	}
}