// CalcPI3.java 
class CalcPI3 
{ 
public static void main (String [] args) 
{ 
MyThread mt = new MyThread (); 
mt.start (); 
try 
{ 
mt.join (); 
} 
catch (InterruptedException e) 
{ 
} 
System.out.println ("pi = " + mt.pi); 
} 
} 
class MyThread extends Thread 
{ 
boolean negative = true; 
double pi; //缺省初始化成0.0 
public void run () 
{ 
for (int i = 3; i < 100000; i += 2) 
{ 
if (negative) 
pi -= (1.0 / i); 
else 
pi += (1.0 / i); 
negative = !negative; 
} 
pi += 1.0; 
pi *= 4.0; 
System.out.println ("Finished calculating PI"); 
} 
}