applet1.java

模拟球的自由落体

import java.awt.*;
import java.applet.Applet;
import java.awt.event.*;
import java.math.*;
public class Applet1 extends Applet implements ActionListener
{
	int h,t,a,b,k=10000;
	Button btn;
	public void paint(Graphics g)
	{
		g.setColor(Color.black);
		g.drawLine(10,145,140,145);
		g.setColor(Color.red);
		g.fillOval(60,130-h+t*t/k-15,30,30);
		if(a==0)t+=50;
		else t-=50;
		if(a==0&&t*t/k>h)
		{
			a=1;
			h=h*3/4;
			t=(int)Math.sqrt((h)*k);
		}
		else if(a==1&&t<0)
		{
			a=0;
			t=0;
		}
		try{
			Thread.sleep(50);
		}
		catch(InterruptedException e)
		{
			showStatus(e.toString());
		}
		if(h!=0&&b==1)repaint();
		else
		{
			h=100;
			b=0;
		}
	}
	public void init()
	{
		b=0;
		h=100;
		btn=new Button("拍");
		add(btn);
		btn.addActionListener(this);
	}
	public void actionPerformed(ActionEvent e)
	{
		if(e.getSource()==btn)
		{
			b=1;
			repaint();
		}
	}
	public void statr()
	{
		h=100;
		b=0;
	}
}