多线程面试题

多线程-用JAVA写一个多线程程序，写四个线程，其中二个对一个变量加1，另外二个对一个变量减1

加1：

import java.util.concurrent.atomic.AtomicLong;

public class SafePlusCounter implements Runnable{
	
	public SafePlusCounter(AtomicLong count){
		plus(count);
	}
	
	public long plus(AtomicLong count){
		long i = count.incrementAndGet();
		System.out.println(i);
		return i;
	}
	
	public void run() {
		
	}
}

　　

减1：

import java.util.concurrent.atomic.AtomicLong;

public class SafeMinusCounter implements Runnable{
	
	public SafeMinusCounter(AtomicLong count){
		minus(count);
	}
	
	public long minus(AtomicLong count){
		long i = count.decrementAndGet();
		System.out.println(i);
		return i;
	}

	public void run() {
	}
	
}

　　在main方法启多线程，一共4个，两加两减：

public class SafeCounting {
	
	public static void main(String[] args) throws InterruptedException {
		 final AtomicLong count = new AtomicLong(0);
		for(int i=0;i<100;i++){
			SafePlusCounter plusCounter1 = new SafePlusCounter(count);
			SafePlusCounter plusCounter2 = new SafePlusCounter(count);
			SafeMinusCounter minusCounter1 = new SafeMinusCounter(count);
			SafeMinusCounter minusCounter2 = new SafeMinusCounter(count);
			new Thread(plusCounter1).start();
			new Thread(plusCounter2).start();
			new Thread(minusCounter1).start();
			new Thread(minusCounter2).start();
		}
		System.out.println("final 结果 "+count);
	}
}