要實現執行緒範圍內的資料共享，就是說不管是A模組還是B模組，如果它們現在在同一個執行緒上執行，它們操作的資料應該是同一個，下面的做法就不行：

package javaplay.thread.test;

import java.util.Random;

public class ThreadScopeShareData {

	private static int data = 0;

	public static void main(String[] args) {
		for (int i = 0; i < 2; i++) {
			new Thread(new Runnable() {

				@Override
				public void run() {
					data = new Random().nextInt();
					System.out.println(Thread.currentThread().getName() + " has put data : " + data);
					new A().get();
					new B().get();
				}

			}).start();

		}
	}

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

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

}
 

output:

Thread-0 has put data : 840132982
Thread-1 has put data : -1767656158
A from Thread-0 get data : -1767656158
A from Thread-1 get data : -1767656158
B from Thread-0 get data : -1767656158
B from Thread-1 get data : -1767656158

在這個執行緒範圍內，不管哪個模組去取這個變數拿到的都是同一個變數；換了另外一個執行緒就是另外一份資料了；即執行緒內共享，執行緒外獨立；

package javaplay.thread.test;

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

public class ThreadScopeShareData {

	private static int data = 0;
	private static Map<Thread, Integer> threadData = new HashMap<Thread, Integer>();

	public static void main(String[] args) {
		for (int i = 0; i < 2; i++) {
			new Thread(new Runnable() {

				@Override
				public void run() {
					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);
		}
	}

}
 

output:

Thread-0 has put data : -74463225
Thread-1 has put data : -2119679267
A from Thread-1 get data : -2119679267
A from Thread-0 get data : -74463225
B from Thread-1 get data : -2119679267
B from Thread-0 get data : -74463225

資料庫的連線就是一個典型的應用