自己实现一个ThreadLocal

public class 

> UserThreadLocal

<T> {
    Map<Thread,T> thenCurrMap=new HashMap<>();

    public void Set(T v){
        thenCurrMap.put(Thread.currentThread(),v);
    }

    public T get(){
        return thenCurrMap.getOrDefault(Thread.currentThread(),null);
    }

    static volatile int number=0;
    public static void main(String[] args) {
        UserThreadLocal<Integer> userThreadLocal=new UserThreadLocal<>();


        for (int i=0;i<10;i++){

            new Thread(new Runnable() {
                @Override
                public void run() {
                    userThreadLocal.Set(number++);

                    System.out.println(userThreadLocal.get());
                }
            }).start();
        }
    }

}