learning java Objects.requireNonNull 当传入参数为null时，该方法返回参数本身

        System.out.println(Objects.hashCode(obj));
        System.out.println(Objects.toString(obj));
        System.out.println(Objects.requireNonNull(obj, "obj参数不能为空"));

output:

0
null
Exception in thread "main" java.lang.NullPointerException: obj参数不能为空
    at java.base/java.util.Objects.requireNonNull(Objects.java:246)
    at ObjectTest.main(ObjectTest.java:9)