java ThreadLocal 理解

一 ThreadLocal  有什么用

 ThreadLocal并不是一个Thread，而是Thread的局部变量。

 ThreadLocal 对多线程提供了另一种思路：给线程产生一个特殊的"局部变量"，绑定到线程，随着线程的改变 get()方法得到value也改变。例如在线程1里面用 threadLocal.get()方法,得到的就是线程1的value；线程2里面用 threadLocal.get().get()方法,得到的就是线程2的value。threadLocal.get()倒地得到的value是多少取决于你在哪个线程下用 threadLocal.set（value）；

 

public class ThreadLocal1 {

public class ThreadLocal1 {
    public String s ;
    public static void main(String[] args) throws InterruptedException {
        int a=0;
        int b=0;
       Variable v = new Variable();
       Vector<Integer> arrayList = new Vector<>();
        // 启动100个线程 并且传入变量
        for (int i = 0; i < 100; i++) {
           Thread thread =  new T1(v,i,i,arrayList);
           thread.start();
            a=a+i+i;
        }

        Thread.sleep(1000);
        arrayList.sort(null);
        for (int i = 0; i < 100; i++) {
            b+=arrayList.get(i);
            // 输出m方法的返回值
            System.out.print(arrayList.get(i)+",");
        }

        System.out.println();
        System.out.println("a的和"+a);
        System.out.println("b的和"+b);
    }
}
class Variable{
    public ThreadLocal<Integer> l1 = new ThreadLocal<>();
    public ThreadLocal<Integer> l2 = new ThreadLocal<>();
    public int m(){
        //System.out.println(l1.get()+l2.get());
        return l1.get()+l2.get();
    }
}
class T1 extends Thread{
    Variable v = null;
    int a,b;
    Vector<Integer> arrayList = null;
    T1(){

    }
    T1(Variable v,int a ,int b,Vector<Integer> arrayList){
       this.v = v;
       this.a = a;
       this.b=b;
       this.arrayList = arrayList;
    }
    @Override
    public void run() {
        // 对v对象的值进行  值传递
            v.l1.set(new Integer(a));
            v.l2.set(new Integer(b));
            arrayList.add(v.m());
    }
}

String s ; public static void main(String[] args) throws InterruptedException { int a=0; int b=0; Variable v = new Variable(); Vector<Integer> arrayList = new Vector<>(); for (int i = 0; i < 100; i++) { Thread thread = new T1(v,i,i,arrayList); thread.start(); a=a+i+i; } Thread.sleep(1000); arrayList.sort(null); for (int i = 0; i < 100; i++) { b+=arrayList.get(i); System.out.print(arrayList.get(i)+","); } System.out.println(); System.out.println("a的和"+a); System.out.println("b的和"+b); } } class Variable{ public ThreadLocal<Integer> l1 = new ThreadLocal<>(); public ThreadLocal<Integer> l2 = new ThreadLocal<>(); public int m(){ //System.out.println(l1.get()+l2.get()); return l1.get()+l2.get(); } } class T1 extends Thread{ Variable v = null; int a,b; Vector<Integer> arrayList = null; T1(){ } T1(Variable v,int a ,int b,Vector<Integer> arrayList){ this.v = v; this.a = a; this.b=b; this.arrayList = arrayList; } @Override public void run() { v.l1.set(new Integer(a)); v.l2.set(new Integer(b)); System.out.println(Thread.currentThread().getName()); arrayList.add(v.m()); } }