Question

Methods enforced by the set interface:

import java.util.Iterator;

public interface Set<E> {
   
   /**
      Removes all of the elements from this set
   */
   void clear();
   
   /**
      Returns true if this set contains no elements
      @return true if this set contains no elements
   */
   boolean isEmpty();
   
   /**
      Returns the number of elements in this set (its cardinality)
      @return the number of elements in this set
   */
   int size();
   
   /**
      Returns an iterator over the elements in this set
      @return an iterator over the elements in this set
   */
   Iterator<E> iterator();

   /**
      Returns true if this set contains the specified element
      @param e element whose presence in this set is to be tested
      @return true if this set contains the specified element
   */
   boolean contains (E e);
   
   /**
      Adds the specified element to this set if it is not already present
      @param e element to be added to this set
      @return true if this set did not already contain the specified element
   */
   boolean add (E e);
   
   /**
      Removes the specified element from this set if it is present
      @param e element to be removed from this set, if present
      @return true if this set contained the specified element
   */
   boolean remove (E e);
}
   

Answer 1

EXPLAINATION TO THE ABOVE PROGRAM:

JAVA SET:
i. Set is an interface which extends Collection.
ii.   It is an unordered collection of objects in which duplicate values cannot be stored.
iii. Set has various methods to add, remove clear, size, etc to enhance the usage of it.
THE SET INTERFACE:
i.   Java Set interface is a member of the Java Collections Framework.
ii.   Unlike List, Set DOES NOT allow you to add duplicate elements.
iii.   Set allows us to add at most one null element only.
iv.   Set interface got one default method in Java 8: spliterator.
v.   Unlike List and arrays, Set does NOT support indexes or positions of it’s elements.
vi.   Set supports Generics and we should use it whenever possible. Using Generics with Set will avoid ClassCastException at run-time.
vii.   We can use Set interface implementations to maintain unique elements.
The Java platform contains three general-purpose Set implementations:
⦁   HashSet
⦁   TreeSet
⦁   LinkedHashSet
HashSet, which stores its elements in a hash table, is the best-performing implementation; however it makes no guarantees concerning the order of iteration.
TreeSet, which stores its elements in a red-black tree, orders its elements based on their values; it is substantially slower than HashSet.
LinkedHashSet, which is implemented as a hash table with a linked list running through it, orders its elements based on the order in which they were inserted into the set .
SET INTERFACE OPERATIONS:

Set Interface operations are use to implement some tasks like:
⦁   The size operation returns the number of elements in the Set.
⦁   The add method adds the specified element to the Set if it is not already present and returns a boolean indicating whether the element was added.
⦁   The remove method removes the specified element from the Set if it is present and returns a boolean indicating whether the element was present.
⦁   The iterator method returns an Iterator over the Set.
Iterating Elements:
In Java, Iterator is an interface available in Collection framework in java. util package. It is a Java Cursor used to iterate a collection of objects. It is used to traverse a collection object elements one by one.We import "Java.util.Iterator" package to perform this process.
The same as with lists, although possible to iterate with for and enhanced-for loops, it's better to use the Java Collections' Iterator.
JAVA SET METHODS:
1.   int size(): to get the number of elements in the Set.
2.   boolean isEmpty(): to check if Set is empty or not.
3.   boolean contains(Object o): Returns true if this Set contains the specified element.
4.   Iterator iterator(): Returns an iterator over the elements in this set. The elements are returned in no particular order.
5.   Object[] toArray(): Returns an array containing all of the elements in this set. If this set makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
6.   boolean add(E e): Adds the specified element to this set if it is not already present (optional operation).
7.   boolean remove(Object o): Removes the specified element from this set if it is present (optional operation).
8.   boolean removeAll(Collection c): Removes from this set all of its elements that are contained in the specified collection (optional operation).
9.   boolean retainAll(Collection c): Retains only the elements in this set that are contained in the specified collection (optional operation).
10.   void clear(): Removes all the elements from the set.
11.   Iterator iterator(): Returns an iterator over the elements in this set.

SET INTERFACE BULK OPERATIONS:
Bulk operations are particularly well suited to Sets. when applied, they perform standard set-algebraic operations.
Suppose s1 and s2 are sets. Here's what bulk operations do:
⦁   s1.containsAll(s2) — returns true if s2 is a subset of s1. Here, s2 is a subset of s1 if set s1 contains all of the elements in s2.
⦁   s1.addAll(s2) — transforms s1 into the union of s1 and s2. Here,The union of two sets is the set containing all of the elements contained in either set.
⦁   s1.retainAll(s2) — transforms s1 into the intersection of s1 and s2. Here,The intersection of two sets is the set containing only the elements common to both sets.
⦁   s1.removeAll(s2) — transforms s1 into the set difference of s1 and s2.