ThreadLocal的空指针异常

public class ThreadLocalNPE {
    ThreadLocal<Long> longThreadLocal = new ThreadLocal<Long>();
    public void set() {
        longThreadLocal.set(Thread.currentThread().getId());
    }
    /**
     * set之前使用get方法时，get正常情况下返回null，但是直接抛出空指针异常了，原因是Long是包装类型，long是基本类型，在进行类型转换报了错
     * 而不是get方法的原因。
     * 解决方式是：将返回值 long改为Long
     * @return
     */
    public Long get() {
        return longThreadLocal.get();
    }
    public static void main(String[] args) {
        ThreadLocalNPE threadLocalNPE = new ThreadLocalNPE();
        System.out.println(threadLocalNPE.get());
        Thread thread = new Thread(() -> {
            threadLocalNPE.set();
            System.out.println(threadLocalNPE.get());
        });
        thread.start();
    }
}