设计4个线程，其中两个线程每次对j增加1，另外两个线程对j每次减少

public class ThreadTest1{   
	private int j;    
	public static void main(String args[]){ 
		ThreadTest1 tt=new ThreadTest1(); 
		Inc inc=tt.new Inc(); 
		Dec dec=tt.new Dec(); 
		for(int i=0;i<2;i++){  
		  Thread t=new Thread(inc); 
		  t.start();  
		  t=new Thread(dec); 
		  t.start(); 
		} 
	}    
	private synchronized void inc(){ 
		j++;  
		System.out.println(Thread.currentThread().getName()+"-inc:"+j);   
	}    
	private synchronized void dec(){ 
		j--;  
		System.out.println(Thread.currentThread().getName()+"-dec:"+j);   
	}    
	class Inc implements Runnable{ 
		public void run(){  
			for(int i=0;i<100;i++){ 
				inc(); 
			} 
		}   
	}    
	class Dec implements Runnable{ 
		public void run(){  
			for(int i=0;i<100;i++){ 
				dec(); 
			}  
		}   
	} 
}