particletree.java

面向对象技术

import java.awt.*;
import java.applet.*;
//定义ParticleTree类
public class ParticleTree extends java.applet.Applet implements Runnable 
{
    fPointTree root; //定义类fPointTree的对象root
    Image      im; //定义Image类
    Graphics   offscreen; //定义一个Graphics类
    Thread     mainThread = null; //定义主线程
    int        width = 200; //定义applet的宽度
    int        height = 300; //定义applet的高度
    int        iteration = 0; 
    double     kVY = -15, kVX = 0; //初始速度
    int        kMaxIteration = 30;
    // 定义参数并赋值
    double     kChanceOfBranchPoint = 0.3;
    double     kScaleAtBranch = 0.7;
//初始化程序    
public void init() {
  resize(width, height);
  try {
    im = createImage(width, height);
    offscreen = im.getGraphics();
  } catch (Exception e) {
    offscreen = null;
  }
  root = new fPointTree((double)width/2, height, kVX, kVY, null, null); 
}
// 使用递归的方法，画出Applet。    
public void paintApplet (Graphics g, fPointTree current) {
    int  i;
    g.setColor(Color.blue);
    if (current.left!=null) {
      g.drawLine((int) current.x, (int) current.y, (int) current.left.x, (int) current.left.y);
      paintApplet(g, current.left);
    }
    if (current.right!=null) {
      g.drawLine((int) current.x, (int) current.y, (int) current.right.x, (int) current.right.y);
      paintApplet(g, current.right);
    }
}
//更新数据
public void update(Graphics g) {
    paint(g);
}
//paint()方法
public void paint(Graphics g) {
    if (offscreen != null) {
	offscreen.setColor(Color.white);
    	offscreen.fillRect(0,0, width, height);    
	paintApplet(offscreen, root);
	g.drawImage(im, 0, 0, this);
    }
    else {
	paintApplet(g, root);
    }
}
//启动线程
public void start() {
  if (mainThread == null) {
    mainThread = new Thread(this);
    mainThread.start();
  }
}
//停止线程
public void stop() {
    mainThread.stop();
    mainThread = null;
}
//对整个树作递归操作，当遇到树叶节点时，对该节点添加一个新节点，或者根据自动生成的随机数
//将该节点转化为一个树杈节点，并添加一个左节点和一个右节点。
public void AddOneLevel (fPointTree current) {
  if (current.left==null && current.right==null) {
    if (Math.random() < kChanceOfBranchPoint) {
      //如果是一个树杈节点，对该点添加一个左节点和右节点，并且随机地改变该点的速度
      current.left = new fPointTree(current.x + current.vX, 
				    current.y + current.vY,
				    kScaleAtBranch * (current.vX + Math.max(Math.abs(current.vX), Math.abs(current.vY)) * (Math.random() * 0.5 - 0.25)),
				    kScaleAtBranch * (current.vY + Math.max(Math.abs(current.vX), Math.abs(current.vY)) * (Math.random() * 0.5 - 0.25)),
				    null,null);
      current.right = new fPointTree(current.x + current.vX, 
				    current.y + current.vY,
				    kScaleAtBranch * (current.vX + Math.max(Math.abs(current.vX), Math.abs(current.vY)) * (Math.random() * 0.5 - 0.25)),
				    kScaleAtBranch * (current.vY + Math.max(Math.abs(current.vX), Math.abs(current.vY)) * (Math.random() * 0.5 - 0.25)),
				    null,null);
    }
    else {
      //如果不是一个树杈节点，只增加一个新的左节点，不改变该点的速度
      current.left = new fPointTree(current.x + current.vX, 
				    current.y + current.vY,
				    current.vX + Math.max(Math.abs(current.vX), Math.abs(current.vY)) * (Math.random() * 0.5 - 0.25),
				    current.vY + Math.max(Math.abs(current.vX), Math.abs(current.vY)) * (Math.random() * 0.5 - 0.25),
				    null,null);
    }
  }
  else {
    // 如果不在叶子节点上，对整个树继续作递归操作。
    if (current.left!=null)
      AddOneLevel(current.left);
    if (current.right!=null)
      AddOneLevel(current.right);
  }
}
 
//运行
public void run() {
  while (mainThread!=null) {
    try {mainThread.sleep(200);}
    catch (InterruptedException e) {}
    if (iteration < kMaxIteration) {
      repaint();	
      AddOneLevel(root);
    }
    else if (iteration > 1.5 * kMaxIteration) {
      iteration = 0;
      root = new fPointTree((double)width/2, height, kVX, kVY, null, null); 
      repaint();
      AddOneLevel(root);
    }
    iteration++;
    
  }
  mainThread = null;
}
}