What is upcasting?

What is upcasting?

• A. Casting a subclass reference to the same subclass type.
• B. Casting a subclass reference to a superclass type (implicit, always safe)
• C. Explicitly casting aSuperclass reference to a subclass type
• D. Converting an object to a primitive type

Answer: (B)

Upcasting is treating a subclass object as if it were an instance of its superclass by using a reference of the superclass type. This is allowed implicitly in many languages because every subclass is also a superclass, so the object already satisfies the behavior and interface required by the superclass. The actual object remains a subclass instance, but the access is limited to the members the superclass exposes, which enables polymorphism—methods can operate on any subclass instance through a common superclass interface. This is safe and common, and the opposite action would be downcasting, where you cast a superclass reference back to a subclass type, which can fail at runtime if the object isn’t actually that subclass. It doesn’t involve converting to a primitive type; that’s a different kind of casting.

Upcasting is treating a subclass object as if it were an instance of its superclass by using a reference of the superclass type. This is allowed implicitly in many languages because every subclass is also a superclass, so the object already satisfies the behavior and interface required by the superclass. The actual object remains a subclass instance, but the access is limited to the members the superclass exposes, which enables polymorphism—methods can operate on any subclass instance through a common superclass interface. This is safe and common, and the opposite action would be downcasting, where you cast a superclass reference back to a subclass type, which can fail at runtime if the object isn’t actually that subclass. It doesn’t involve converting to a primitive type; that’s a different kind of casting.