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When will instanceof return false

 
Ranch Hand
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instanceof ofcourse returns false when null is used... like null instance of Integer returns false.

Barring that , what are the cases when it returns false..because instanceof gives a compiler error when used between incompatible types.
And when invoked between an object and class belonging to same hierarchy it always returns true.

pls explain.
 
Greenhorn
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class BBB { }
class CCC extends BBB { }
The instanceof operator is useful when it is necessary to find the
runtime type of an object. The declared type might be a supertype.

class DDD extends BBB { }
public class X {
public static void main(String[] args) {
BBB c = new CCC();
BBB d = new DDD();
X.checkIt(c); // prints true
X.checkIt(d); // prints false
}
private static void checkIt(BBB b) {
System.out.println(b instanceof CCC);
}
}
 
Vepa Sritej
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Thanks Allan..
 
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Also you can use "instanceof" operator with interfaces:

reference instanceof InterfaceX

Using instanceof with Interfaces as a second parameter never leads to compile time error. It checks if the reference's Class or up in the hierarchy implements the Inteface.
 
Greenhorn
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when you assign sub class to super class instance then instanceof true or else returns false.If Honda extends Car
if say
car[] c1=new Honda(); that is works fine
 
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