How can I do a safe downcast and prevent a ClassCastException

java casting downcast
code-gijoe picture code-gijoe · Jul 24, 2010 · Viewed 7.8k times · Source

I have the following scenario:

public class A {
}

public class B extends A {
}

public class C extends B {
    public void Foo();
}

I have a method that can return class A, B or C and I want to cast safely to C but only if the class type is C. This is because I need to call Foo() but I don't want the ClassCastException.

Answer

Simon Nickerson picture Simon Nickerson · Jul 24, 2010

Can you do this?

if (obj instanceof C) {
   ((C)obj).Foo();
}
else {
   // Recover somehow...
}

However, please see some of the other comments in this question, as over-use of instanceof is sometimes (not always) a sign that you need to rethink your design.

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