java 之 线程间变量共享

import java.util.Random;

public class StaticTest {

	private static int data = 0;

	public static void main(String[] args) {
		//开三个线程
				for(int i=0;i<3;i++) {
					new Thread(new Runnable() {

						@Override
						public void run() {
							//每个线程data值都一样，下边的程序有解释
						 data = new Random().nextInt();
							System.out.println(Thread.currentThread().getName() + " has put data ："+ data);
						}

					}).start();
				}
	}

}

运行结果：

Thread-1 has put data ：367396051
Thread-2 has put data ：367396051
Thread-0 has put data ：367396051

import java.util.HashMap;
import java.util.Map;
import java.util.Random;


public class ThreadScopeShareData {

	//静态，会造成一样的随机值，此处有点不理解
	private static int data = 0;
	//以线程作为key
	private static Map<Thread,Integer> threadData = new HashMap<Thread, Integer>();

	public static void main(String[] args) {
		//开三个线程
		for(int i=0;i<3;i++) {
			new Thread(new Runnable() {

				@Override
				public void run() {
					//每个线程data值都一样，因为是静态变量，一改全改，最后的结果跟最后的线程data值一样
					//被后来的线程data值覆盖了，因为静态变量只有一份
//					data = new Random().nextInt();
					//这样就不同了
					int data = new Random().nextInt();
					System.out.println(Thread.currentThread().getName() + " has put data ："+ data);
					threadData.put(Thread.currentThread(), data);
					new A().get();
					new B().get();
				}

			}).start();
		}
	}
	static class A {
		public void get() {
			int data = threadData.get(Thread.currentThread());
			System.out.println("A from  "+Thread.currentThread().getName()+" get data : " +data);
		}
	}

	static class B {
		public void get() {
			int data = threadData.get(Thread.currentThread());
			System.out.println("B from  "+Thread.currentThread().getName()+" get data : " +data);
		}
	}
}

map模拟了ThreadLocal。

运行结果：

Thread-0 has put data ：1500573848
Thread-2 has put data ：1307429900
Thread-1 has put data ：-1173968999
A from  Thread-1 get data : -1173968999
A from  Thread-0 get data : 1500573848
A from  Thread-2 get data : 1307429900
B from  Thread-1 get data : -1173968999
B from  Thread-0 get data : 1500573848
B from  Thread-2 get data : 1307429900