Will null instanceof SomeClass return false or throw a NullPointerException?
转载于:https://stackoverflow.com/questions/2950319/is-null-check-needed-before-calling-instanceof
Using a null reference as the first operand to instanceof returns false.
No, it's not. instanceof would return false if its first operand is null.
No. Java literal null is not an instance of any class. Therefore it can not be an instanceof any class. instanceof will return either false or true therefore the <referenceVariable> instanceof <SomeClass> returns false when referenceVariable value is null.
Just as a tidbit:
Even (((A)null)instanceof A) will return false.
(If typecasting null seems surprising, sometimes you have to do it, for example in situations like this:
public class Test
{
public static void test(A a)
{
System.out.println("a instanceof A: " + (a instanceof A));
}
public static void test(B b) {
// Overloaded version. Would cause reference ambiguity (compile error)
// if Test.test(null) was called without casting.
// So you need to call Test.test((A)null) or Test.test((B)null).
}
}
So Test.test((A)null) will print a instanceof A: false.)
P.S.: If you are hiring, please don't use this as a job interview question. :D