Casting down

[zaher]

Hi,
//------------------------------------
class Parent{}
class Child extends Parent{}

class A {
public static void main(String[] s)
{
Parent p = new Parent();
Child c = (Child) p; // compiles fine
//but gives a cast Exception at runtime
}
}
Can you explain why it is giving a cast exception at runtime please?
Thank you

[Edwin Keeton]

Because p is not in fact a Child but a Parent. At compile-time the compiler "trusts" you when you cast down, but at run-time the object that you cast better actually be what you said it was or you'll get a runtime exception.

[zaher]

Thank you . It's clear now

[RaviKumar Golagani]

Hi,
At compile-time the compiler "trusts" you when you cast down, but at run-time it finds that you are Casting with the parent object,since both are incompatible or you'll get a runtime exception.
Child c = (Child) p;
By above line of code, it is nothing but saying parent = child,which is wrong.Parent can have all the properties of the child,but child cannot have all the properties of the parent.
Cheers,
Ravi

[Valentin Crettaz]

zaher,
Welcome to Javaranch, a friendly place for Java greenhorns
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Thanks Pardner! Hope to see you 'round the Ranch!