java - 在调用instanceof之前是否需要进行null检查？(Is null check needed before calling instanceof?)

Question

null instanceof SomeClass返回false还是抛出NullPointerException ？

  ask by Johan Lübcke translate from so

Answer 1

No, a null check is not needed before using instanceof.

(不，使用instanceof之前不需要进行空检查。)

The expression x instanceof SomeClass is false if x is null .

(如果x为null则表达式x instanceof SomeClass为false 。)

From the Java Language Specification, section 15.20.2, "Type comparison operator instanceof" :

(根据Java语言规范的第15.20.2节“类型比较运算符instanceof” ：)

"At run time, the result of the instanceof operator is true if the value of the RelationalExpression is not null and the reference could be cast to the ReferenceType without raising a ClassCastException . Otherwise the result is false ."

(“在运行时，结果instanceof运算符是true ，如果RelationalExpression的值不null ，并引用可以转换为引用类型不提高一个ClassCastException 。否则，结果是false 。”)

So if the operand is null, the result is false.

(因此，如果操作数为null，则结果为false。)