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Use instanceof carefully
interface MyInterface{}
class A{}
public class B{
public static void main(String[] args) {
B b = new B();
if (b instanceof MyInterface){
System.out.println("b is MyInterface");
}
}
}
This code will compile. Althougt the condition b instanceof MyInterface
will not succeed the code will compile. But when we add the following condition:
if (b instanceof A){
System.out.println("b is A");
}
compilation fails. The class B must be on the same path of inheritance tree with class A. In order to make such comparision class B must be subclass of A, or class A must be subclass of B. If we add extends A to the declaration of class B the condition b instanceof A
will return true. If we add extends B
to the declaration of class A, the condition b instanceof A
will not succeed, but in both cases compilation will succeed.
For interfaces there are not such restriction. You can check an instance of any class against any interface.
Author: Jafar N.Aliyev (Jsoft)
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