When can an object reference be cast to an interface reference?

When can an object reference be cast to an interface reference?

• A. When the object is of a primitive type.
• B. When the object implements the referenced interface.
• C. When the object is null.
• D. When the object belongs to the same package as the interface.

Answer: (B)

An object reference can be cast to an interface reference when the object implements the referenced interface. This is because, in Java, interfaces define a contract that classes can implement. When a class implements an interface, it guarantees that it will provide the methods defined by that interface. Therefore, if you have an object of a class that implements a specific interface, you can safely cast that object to the interface type, allowing you to use the interface's methods. For instance, consider an interface named "Animal" and a class "Dog" that implements this interface. When you create an object of the "Dog" class, you can cast it to the "Animal" interface type because "Dog" adheres to the contract defined by "Animal". This not only allows polymorphism but is also a core feature of Java's implementation of interfaces and inheritance. Additionally, it's crucial to note that casting to an interface type is not valid if the object does not implement that interface, which is why the other choices do not hold up in this context.

An object reference can be cast to an interface reference when the object implements the referenced interface. This is because, in Java, interfaces define a contract that classes can implement. When a class implements an interface, it guarantees that it will provide the methods defined by that interface. Therefore, if you have an object of a class that implements a specific interface, you can safely cast that object to the interface type, allowing you to use the interface's methods.

For instance, consider an interface named "Animal" and a class "Dog" that implements this interface. When you create an object of the "Dog" class, you can cast it to the "Animal" interface type because "Dog" adheres to the contract defined by "Animal". This not only allows polymorphism but is also a core feature of Java's implementation of interfaces and inheritance.

Additionally, it's crucial to note that casting to an interface type is not valid if the object does not implement that interface, which is why the other choices do not hold up in this context.