Explain ThreadLocal in detail

One 、 brief introduction

ThreadLocal Provide thread local variables . These variables are different from normal variables , Because every thread is accessing ThreadLocal At instance time 《 Through its getiset Method ) All have their own 、 Independently initialized variable copies .ThreadLocal Instances are usually private static fields in a class , The purpose of using it is to hope that the State 《 for example , user lID Or business ID) Associated with threads .

The main methods are as follows ：

Two 、 Small case demo

class Hourse{ 
    
    // Not recommended at work 
// ThreadLocal<Integer> saleValue = new ThreadLocal(){ 
    
// @Override
// protected Integer initialValue() { 
    
// return 0;<