int primitivI[] = {1,1,1};
Integer wrapperI[] = {2,22,2};
1. System.out.println(primitivI instanceof Object);//true
2. System.out.println(primitivI instanceof Object[]);//Compilation Error Why ????
3. System.out.println(wrapperI instanceof Object);//true
4. System.out.println(wrapperI instanceof Object[]);//true
Here I have two arrays of integer (primitve,Wrapper) type but I have got different result for instanceof operator
see the line number 2 and 4
line no 4 will compile successfully and give result true but in case of line 2, why does it result in a compilation error?
From line 1 and 3 it is clear that the two arrays are instanceof object but in case of Object[], why do the
results differ?
JLS 15.20.2. says :
If a cast of the RelationalExpression to the ReferenceType would be rejected as a compile-time error, then the instanceof relational expression likewise produces a compile-time error. In such a situation, the result of the instanceof expression could never be true.
That means that if at compile time the compiler knows that X cannot be instanceof Y, the expression X instanceof Y would give a compile time error.
You can get simpler examples that don't compile, without trying with arrays :
String s = "dgd";
System.out.println(s instanceof Integer);
Similarly, your 2nd example doesn't compile, since int[] cannot be cast to Object[]. All your other examples compile, since primitivI can be cast to Object and wrapperI can be cast to both Object and Object[].