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javanullpointerexceptionnull

Is null check needed before calling instanceof?

Will null instanceof SomeClass return false or throw a NullPointerException?

Solution

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

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

    The Java 11 Language Specification expresses this concisely in section 15.20.2, "Type comparison operator instanceof". (Java 17 expresses this less concisely, after the introduction of instanceof pattern matching.)

    "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."

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