Java rules for casting

Question

When can a certain object be cast into another object? Does the casted object have to be a subtype of the other object? I'm trying to figure out the rules...

Edit: I realized that I didn't explain my issue at all: basically I am casting an object to an interface type. However, at run-time, I get a java.lang.ClassCastException. What needs to happen with my object so that I can cast it to this interface? Does it have to implement it?

Thanks

Answer 1

In Java there are two types of reference variable casting:

• Downcasting: If you have a reference variable that refers to a subtype object, you can assign it to a reference variable of the subtype. You must make an explicit cast to do this, and the result is that you can access the subtype's members with this new reference variable.

• Upcasting: You can assign a reference variable to a supertype reference variable explicitly or implicitly. This is an inherently safe operation because the assignment restricts the access capabilities of the new variable.

Yes, you need to implement the interface directly or indirectly to enable assigning your class object reference to the interface type.