In Java, can I use a primitive type literal or type variable in an instanceof expression?

Question

Can I use a primitive type literal or type variable in an instanceof expression?

class MyClass {
    {
         boolean b1 = null insta         


        

Answer 1

1. You can't do it.
2. Even if you could, you can't use it.

A typical usage of instanceof looks like

void somemethod(Collection c) {
    if (c instanceof List) {...}
}

somemethod(new ArrayList());

The important thing here is that you get an object of a supertype (here: Collection) which may or may not be instance of a subtype (here: List). With primitives this is impossible:

void anothermethod(double x) {
    .... // <------ X
}

anothermethod(42);

At the point X there's a variable x of type double, there's no hidden information about some int 42. The actual parameter 42 didn't masquerade as double, it's got converted to a double. That's why instanceof makes no sense for primitives.