5.1.5 Narrowing Reference Conversions

The following conversions are called the narrowing reference conversions:

• From any class type S to any class type T, provided that S is a superclass of T. (An important special case is that there is a narrowing conversion from the class type Object to any other class type.)
• From any class type S to any interface type K, provided that S is not final and does not implement K. (An important special case is that there is a narrowing conversion from the class type Object to any interface type.)
• From type Object to any array type.
• From type Object to any interface type.
• From any interface type J to any class type T that is not final.
• From any interface type J to any class type T that is final, provided that T implements J.
• From any interface type J to any interface type K, provided that J is not a subinterface of K and there is no method name m such that J and K both declare a method named m with the same signature but different return types.
• From any array type SC[] to any array type TC[], provided that SC and TC are reference types and there is a narrowing conversion from SC to TC.

Such conversions require a test at run time to find out whether the actual reference value is a legitimate value of the new type. If not, then a ClassCastException is thrown.