ThreadLocal：每个线程自身的存储本地、局部区域，类似于容器,每个线程都会在其中有一定存储空间
常用的方法get/set/initialValue
官方建议为private static
每个线程存储自己的数据，更改不会影响其他线程
ThreadLocal 子类InheritableThreadLocal：
继承上下文环境的数据

public class my {//Integer 初始值为null//private static ThreadLocal<Integer> threadlocal=new ThreadLocal<>();//更改初始值需要创建ThreadLocal的子类重写initialValue或者使用lambda(jdk8)private static ThreadLocal<Integer> threadlocal=new ThreadLocal <Integer>() {//父类匿名内部类重写方法 protected Integer initialValue() { return 200; } };//private static ThreadLocal<Integer> threadlocal=new ThreadLocal.withInitial(()->200);public static void main(String[]args) throws InterruptedException{ //获取值 System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get()); //设置值 threadlocal.set(99); System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get()); new Thread(new test()).start(); new Thread(new test()).start();}public static class test implements Runnable{ public void run() { threadlocal.set((int)(Math.random()*100)); System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get()); }}}

每个线程自身的数据更改不会影响其他线程

public class my {private static ThreadLocal<Integer> threadlocal=new ThreadLocal <Integer>() {//父类匿名内部类重写方法 protected Integer initialValue() { return 1; } };public static void main(String[]args) throws InterruptedException{ for(int i=0;i<5;i++) { new Thread(new test()).start(); }}public static class test implements Runnable{ public void run() { //修改不会影响其他线程 Integer left=threadlocal.get(); System.out.println(Thread.currentThread().getName()+"-->"+left); threadlocal.set(left-1); System.out.println(Thread.currentThread().getName()+"还剩下"+threadlocal.get()); }}}

分析ThreadLocal运行环境:

public class my {private static ThreadLocal<Integer> threadlocal=new ThreadLocal <Integer>() {//父类匿名内部类重写方法 protected Integer initialValue() { return 1; } };public static void main(String[]args) throws InterruptedException{ new Thread(new test()).start();//两个打印的内容在不同的线程里 //当start()之后，线程才从main转换到其他线程，所以构造器里的是main线程的}public static class test implements Runnable{ public test() { threadlocal.set(100); //属于main线程，修改不会影响start内的线程 System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get()); } public void run() { System.out.println(Thread.currentThread().getName()+"还剩下"+threadlocal.get()); }}}

子类InheritableThreadLocal:

public class my {private static ThreadLocal<Integer> threadlocal=new InheritableThreadLocal<>();public static void main(String[]args) throws InterruptedException{ System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get()); threadlocal.set(2); //此线程由main线程开辟，拷贝一份main线程的数据给此线程 //即将main线程里的2给此线程 new Thread(()->{ System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get()); threadlocal.set(200); System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get()); }).start();}}