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class A { public static void main(String...args) { Integer var = 10; if(var instanceof Character) // Line1 System.out.println("var is a Character"); } } I know Line 1 will not compile because the compiler has found that var is not a Character.
What I fail to understand is why the compiler throws an error instead of returning false or true.
If the compiler returns false or true (i.e treating the instanceof operation like a regular if-based validation), then it be much more useful.. would it not?
Or am I missing something obvious?
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Probably most of you have already heard that using “instanceof” is a code smell and it is considered as a bad practice. While there is nothing wrong in it and may be required at certain times, but the good design would avoid having to use this keyword.
The instanceof operator in Java is used to check whether an object is an instance of a particular class or not. objectName instanceOf className; Here, if objectName is an instance of className , the operator returns true . Otherwise, it returns false .
The java instanceof operator is used to test whether the object is an instance of the specified type (class or subclass or interface). The instanceof in java is also known as type comparison operator because it compares the instance with type. It returns either true or false.
Having a chain of "instanceof" operations is considered a "code smell". The standard answer is "use polymorphism".
It's a compilation error in accordance with JLS §15.20.2:
If a cast of the RelationalExpression to the ReferenceType would be rejected as a compile-time error, then the
instanceofrelational expression likewise produces a compile-time error. In such a situation, the result of theinstanceofexpression could never be true.
RelationalExpression is the first operand of instanceof and ReferenceType is the second.
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