Java – Set Interface – Ameerpet Technologies

Set:

Set doesn’t allow duplicates.
Set is not index based.

HashSet Methods are:

boolean add(E e)	Adds the specified element to this set if it is not already present.
void clear()	Removes all of the elements from this set.
Object clone()	Returns a shallow copy: the elements themselves are not cloned.
boolean contains(Object o)	Returns true if this set contains the specified element.
boolean isEmpty()	Returns true if this set contains no elements.
Iterator<E> iterator()	Returns an iterator over the elements in this set.
boolean remove(Object o)	Removes the specified element from this set if it is present.
int size()	Returns the number of elements in this set (its cardinality).

Note: Set is not providing any methods to perform index-based operations.

Implementations are:

HashSet: It doesn’t maintain insertion order
LinkedHashSet: It maintains insertion order of elements.
TreeSet: It maintains sorted order of elements.

Program to store elements into HashSet and display:

import java.util.*;
class Code
{
            public static void main(String[] args) {
                        Set<Integer> set = new HashSet<Integer>();
                        set.add(50);
                        set.add(40);
                        set.add(30);
                        set.add(20);
                        set.add(10);
                        System.out.println(“Set : ” + set);
            }
}
Output: Random order of elements

Program to store elements into LinkedHashSet and display:

import java.util.*;
class Code
{
            public static void main(String[] args) {
                        Set<Integer> set = new LinkedHashSet<Integer>();
                        set.add(50);
                        set.add(40);
                        set.add(30);
                        set.add(20);
                        set.add(10);
                        System.out.println(“Set : ” + set);
            }
}
Output: 50, 40, 30, 20, 10

Program to store elements into TreeSet and display:

import java.util.*;
class Code
{
            public static void main(String[] args) {
                        Set<Integer> set = new TreeSet<Integer>();
                        set.add(50);
                        set.add(40);
                        set.add(30);
                        set.add(20);
                        set.add(10);
                        System.out.println(“Set : ” + set);
            }
}
Output: 10, 20, 30, 40, 50

Remove duplicates in ArrayList:

ArrayList is ordered and allow duplicates.
To remove duplicates in array, we simply convert into Set and display

import java.util.*;
class Code
{
            public static void main(String[] args) {
                        List<Integer> list = new ArrayList<Integer>();
                        for(int i=1 ; i<=4 ; i++) {
                                    list.add(i+2);
                                    list.add(i+3);
                        }
                        System.out.println(“List : ” + list);
                        Set<Integer> set = new HashSet<Integer>(list);
                        System.out.println(“Set : ” + set);
            }
}

Output:    List : [3, 4, 4, 5, 5, 6, 6, 7]
                 Set : [3, 4, 5, 6, 7]

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