学步园

public class Pi_thread extends Thread{

 private int start_wy;
 private int num_steps_wy=100000000;
 double step,x,sum = 0.0;
 public Pi_thread(int start)
 {
	this.start_wy=start;
 }
 public void run() 
{
  
  int i;
  step=1.0/(double)num_steps_wy;
  for(i=start_wy;i<num_steps_wy;i+=2)
  {
   x=(i+0.5)*step;
   sum=sum+4.0/(1.0+x*x);
  }

 }
 public void seril_pi()
 {
  int i;
  step=1.0/(double)num_steps_wy;
  for(i=1;i<num_steps_wy;i++)
  {
   x=(i+0.5)*step;
   sum=sum+4.0/(1.0+x*x);
  }
 }

 public static void main(String[] args) throws InterruptedException {

  double pi_wy,sum_wy=0.0,seri_t_wy,para_t_wy;


  Pi_thread thread1=new Pi_thread(1);
  Pi_thread thread2=new Pi_thread(2);

  double t1=System.currentTimeMillis();

  thread1.start();
  thread2.start();
  thread1.join();
  thread2.join();

  double t2=System.currentTimeMillis();

  sum_wy=thread1.sum+thread2.sum;
  pi_wy=thread1.step*sum_wy;
  para_t_wy=t2-t1;
  System.out.println("并行结果: "+pi_wy);
  System.out.println("并行时间: "+para_t_wy);
  
  Pi_thread thread3=new Pi_thread(3);

  t1=System.currentTimeMillis();

  thread3.seril_pi();

  t2=System.currentTimeMillis();

  pi_wy=thread3.sum*thread3.step;

  seri_t_wy=t2-t1;
  System.out.println("窜行结果： "+pi_wy);
  System.out.println("串行时间： "+seri_t_wy);
  System.out.println("加速比： "+(seri_t_wy/para_t_wy));
  
 }

}

并行结果: 3.1415926135900225
并行时间: 484.0
窜行结果： 3.1415926135904266
串行时间： 1000.0
加速比： 2.0661157024793386