ThreadLocal線程局部變量

與之前寫的Unsafe一樣，都是為了解決并發通路變量的問題。與synchronized等加鎖不同的，ThreadLocal完全不提供鎖，而是利用空間換時間，為每個線程都提供了變量的獨立副本，保障線程安全。

package com.chen.thread;

import java.text.SimpleDateFormat;
import java.util.Random;

/**
 * Created by CHEN on 2016/9/28.
 */
public class ThreadLocalExample implements Runnable {
    //建立一個SimpleDateFormat的本地線程變量
    private static final ThreadLocal<SimpleDateFormat> formatter =
            new ThreadLocal<SimpleDateFormat>() {
        //初始化
                @Override
        protected SimpleDateFormat initialValue() {
            return new SimpleDateFormat("yyyyMMdd HHmm");
        }
    };

    public static void main(String[] args) throws InterruptedException {
        ThreadLocalExample obj = new ThreadLocalExample();
        for (int i = ; i < ; i++) {
            Thread t = new Thread(obj, "" + i);
            Thread.sleep(new Random().nextInt());
            t.start();
        }
    }

    @Override
    public void run() {
        //輸出構造時的變量值
        System.out.println("Thread Name= " + Thread.currentThread().getName() + " default Formatter = " + formatter.get().toPattern());
        try {
            Thread.sleep(new Random().nextInt());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //對目前線程造成影響
        formatter.set(new SimpleDateFormat());
        //影響之後的結果
        System.out.println("Thread Name= " + Thread.currentThread().getName() + " formatter = " + formatter.get().toPattern());
    }

}