Question

Pick a pair of concrete classes in the JDK in a parent-child relationship and discuss a few polymorphic and/or overloaded methods.

Do not use Object as the parent class - it is too trivial to address the issues to be addressed here, and in any case, Object is the final parent of all classes in Java.

Answer 1

One of the examples of parent child relationship in JDK is given as:

The parent class is AbstractSet.java and it is extended by a lot of child classes. Some of them are given as:

• HashSet.java
• HashMap.KeySet
• HashMap.Entryset, etc

Some of the methods overridden by the child classes are given as:

• public Iterator<E> iterator() -> Returns an iterator over the elements in this set. The elements are returned in no particular order.

• public int size() -> Returns the number of elements in this set (its cardinality).

• public boolean isEmpty() -> Returns true if this set contains no elements.

• public boolean contains(Object o) -> Returns true if this set contains the specified element.