What Is Bound in Java

Upper-bound is when you specify (? … extends Field) means argument can be any Field or subclass of Field. Lower-bound is when you specify (? super Field) means argument can be any Field or superclass of Field.

How do you use bound in Java?

To declare a bounded type parameter, list the type parameter’s name, followed by the extends keyword, followed by its upper bound, which in this example is Number . Note that, in this context, extends is used in a general sense to mean either “extends” (as in classes) or “implements” (as in interfaces).

What is bounded wildcards in Java?

A bounded wildcard is one with either an upper or a lower inheritance constraint. The bound of a wildcard can be either a class type, interface type, array type, or type variable. Upper bounds are expressed using the extends keyword and lower bounds using the super keyword.