What does casting mean?

**sev51** · 01-26-2009, 09:13 PM

I don't really understand what is meant by the term casting? I gather that it is converting from one data type to another.. but for example how might you use it for Classes and not necessarily primitive data types??

**angryboy** · 01-26-2009, 10:05 PM

you got it, its converting one data type to another.
all classes are child classes of java.lang.Object, so you can freely cast any class to Object class, or any class within the same family.

**sev51** · 01-27-2009, 12:34 AM

Thanks for the confirmation :)

**Steve11235** · 01-27-2009, 05:31 PM

Casting is used when you, as the developer, have a reference to an object of type ClassA, but you know that the object type is actually of type ClassB, where ClassB extends ClassA.

This comes into play for generic methods that return Object. You want to invoke methods of the actual type, so you have to explicitly cast the Object to MyClass. Essentially, you are telling the compiler you know what you are doing.

At runtime, if the Object is *not* a MyClass, you will get a RunTimeException.