Set Interface in Java

Introduction to Set Interface in Java

Java provides an interface to store and manipulate data known as Collection Interface. The collection is the super interface for a Set interface that helps store any type of object and manipulate it. Set interface stands out as a Collection that does not allows duplicate data in it, i.e. if d1 and d2 are two data entries in the same Set, then the result of d1.equals(d2) should be false. Almost one null element is allowed in Set. Set models the mathematical set abstraction.

Some of the implementations of sets are HashedSet, LinkedHashSet, or TreeSet as sorted representation.

Examples to Implement Set Interface in Java

Below are the examples of Set Interface in Java:

1. HashSet

Code:

import java.util.*;
public class Main{
public static void main(String[] args)
{
// Set demonstration using HashSet
Set<Integer > hash = new HashSet<Integer>();
hash.add(1);
hash.add(4);
hash.add(1);
hash.add(3);
hash.add(2);
System.out.print("Set output without duplicates");
System.out.println(hash);
}
}

Output:

2. TreeSet

Code:

import java.util.*;
public class Main{
public static void main(String[] args)
{
// Set demonstration using TreeSet
Set<Integer> tree = new TreeSet<Integer>();
tree.add(1);
tree.add(4);
tree.add(1);
tree.add(3);
tree.add(2);
System.out.print("Set output without duplicates and sorted data "); System.out.println(tree);
}
}

Output:

Methods of Set Interface in Java

Methods supported by Set for various data object storage and manipulation.

• add(Element e): Adds a specified element in the set.
• addAll(Collection<?> c): Adds all the elements present in the specified collection.
• clear(): Removes all the elements from the set.
• contains(Object o): Returns true if Set contains the same object as the specified object.
• containsAll(Collection<?> c): Returns true if set contains all of the elements in the specified collection.
• size(): Returns the number of elements in the Set.
• equals(Object o): It compares and returns true if our object is equal to the object specified.
• hashCode(): It returns the hashcode value for the set.
• isEmpty(): It returns true if the set contains no element.
• iterator(): It returns an iterator on the set, which helps to trace through the complete set.
• remove(Object o): Removes the specified element from the existing set.
• removeAll(Collection<?> c): Removes the specified collection from the existing set.
• toArray(): It returns the particular array containing all the elements as in Set.

Usage of methods in Our Code:

Code:

import java.util.LinkedHashSet;
public class Main
{
public static void main(String[] args)
{
LinkedHashSet<String> linked = new LinkedHashSet<String>();
// Adding element to LinkedHashSet
linked.add("Apple");
linked.add("Ball");
linked.add("Cat");
linked.add("Dog");
// Cannot add new element as Apple already exists
linked.add("Apple");
linked.add("Egg");
System.out.println("Size of LinkedHashSet: " + linked.size());
System.out.println("Old LinkedHashSet:" + linked);
System.out.println("Remove Dog from LinkedHashSet: " + linked.remove("Dog"));
System.out.println("Trying Remove Zoo which is not present "+ "present: " +        linked.remove("Zoo"));
System.out.println("Check if Apple is present=" + linked.contains("Apple"));
System.out.println("New LinkedHashSet: " + linked);
}
}

Output:

Converting HashSet to TreeSet

HashSet is generally used for search, delete and insert operations. HashSet is faster than TreeSet and uses a hash table. TreeSet whereas used for storing purpose due to its sorted data storage property. TreeSet uses TreeMap from the backend on Java. In order to store sorted data, insert elements into a hashmap and then insert data into a tree to get it sorted.

There are 3 ways to do this:

1. Pass the HashSet created

Code:

import java.util.*;
public class Main
{
public static void main(String[] args)
{
Set<Integer > hash = new HashSet<Integer>();
hash.add(1);
hash.add(4);
hash.add(1);
hash.add(3);
hash.add(2);
System.out.print("HashSet");
System.out.println(hash);
//adding HashSet as a parameter to TreeSet constructor
Set< Integer> treeSet = new TreeSet<>(hash);
// Print TreeSet
System.out.println("TreeSet: " + treeSet);
}
}

Output:

2. Using addAll() method

Code:

import java.util.*;
public class Main
{
public static void main(String[] args)
{
Set<Integer > hash = new HashSet<Integer>();
hash.add(1);
hash.add(4);
hash.add(1);
hash.add(3);
hash.add(2);
System.out.print("HashSet");
System.out.println(hash);
//converting HashSet to TreeSet using addAll() method
Set<Integer> treeSet = new TreeSet<>();
treeSet.addAll(hash);
// Print TreeSet
System.out.println("TreeSet: " + treeSet);
}
}

Output:

3. Using for-each loop

Code:

import java.util.*;
public class Main
{
public static void main(String[] args)
{
Set<Integer > hash = new HashSet<Integer>();
hash.add(1);
hash.add(4);
hash.add(1);
hash.add(3);
hash.add(2);
System.out.print("HashSet");
System.out.println(hash);
//converting HashSet to TreeSet using for each loop
Set<Integer> treeSet = new TreeSet<>();
for (Integer i : hash)
{
treeSet.add(i);
}
// Print TreeSet
System.out.println("TreeSet: " + treeSet);
}
}

Output:

Recommended Article

This is a guide to Set Interface in Java. Here we discuss the Introduction to Set Interface and how it is used to store and manipulate data in Java and its methods. You can also go through our other suggested articles to learn more –

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