Set

Set Interface in Java

Overview

The Set interface in Java represents a collection of unique elements. It is part of the java.util package and extends the Collection interface. Elements in a Set are unordered and do not allow duplicates.

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Characteristics of Set Interface

Feature	Details
Package	java.util
Allows Duplicates	No
Maintains Insertion Order	No (but LinkedHashSet maintains order)
Subinterfaces	NavigableSet
Implementations	HashSet, LinkedHashSet, TreeSet

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Key Features of Set Interface

• No Duplicates: A Set does not allow duplicate elements. If you try to add a duplicate, it will not be inserted.
• Unordered: The elements in a Set are unordered (except for LinkedHashSet and TreeSet).
• Dynamic Size: The size of a Set can grow or shrink as needed.
• Rich API: Provides various methods for adding, removing, and checking elements.

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Initializing Different Types Using the Set Interface

You can initialize a Set with various data types using its implementations like HashSet, LinkedHashSet, etc. Here's how:

Set<Type> stringSet = new HashSet<>();
Set<Type> stringSet = new LinkedHashSet<>();
Set<Type> stringSet = new TreeSet<>();
...
..
.

• Using HashSet _{HashSetDataStructure.java}

  Set<String> stringSet = new HashSet<>();
  Set<Integer> integerSet = new HashSet<>();
  Set<Double> doubleSet = new HashSet<>();

• Using LinkedHashSet _{LinkedHashSetDataStructure.java}

  Set<String> linkedStringSet = new LinkedHashSet<>();
  Set<Integer> linkedIntegerSet = new LinkedHashSet<>();

• Using TreeSet _{TreeSetDataStructure.java}

  Set<String> treeSet = new TreeSet<>();
  Set<Integer> treeIntegerSet = new TreeSet<>();

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Use Cases for Set Implementations

Implementation	Use Case
HashSet	Best for storing unique elements with no concern for order. Example: Storing user IDs.
LinkedHashSet	Maintains insertion order. Example: Storing elements and iterating them in the order they were added.
TreeSet	Stores elements in sorted order. Example: Maintaining a sorted list of elements for quick lookups.

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Commonly Used Methods

Object : Integer, Boolean, String, etc (Every type of objects).

SetType : HashSet, LinkedHashSet, TreeSet, etc (Every type of Set).

Set<Object> set = new SetType<>();

Method	Description	Return Type	Example
add(E e)	Adds the specified element to the set.	boolean	set.add("Hello");
remove(Object o)	Removes the specified element from the set.	boolean	set.remove("Hello");
size()	Returns the number of elements in the set.	int	set.size();
contains(Object o)	Checks if the set contains the specified element.	boolean	set.contains("Hello");
clear()	Removes all elements from the set.	void	set.clear();
isEmpty()	Checks if the set is empty.	boolean	set.isEmpty();
iterator()	Returns an iterator over the elements in the set.	Iterator	Iterator<String> iterator = set.iterator();
toArray()	Converts the set to an array.	Object[]	Object[] arr = set.toArray();
equals(Object o)	Compares the specified object with this set for equality.	boolean	set.equals(obj);
hashCode()	Returns the hash code value for this set.	int	set.hashCode();

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Example Code

import java.util.HashSet;
import java.util.Set;

public class SetInterface {
    public static void main(String[] args) {
        // Create a set
        Set<String> set = new HashSet<>();

        // Add elements
        set.add("Apple");
        set.add("Banana");
        set.add("Cherry");

        // Check if an element exists
        System.out.println("Contains 'Banana': " + set.contains("Banana"));

        // Remove an element
        set.remove("Banana");
        System.out.println("Set after removal: " + set);

        // Check size
        System.out.println("Size of the set: " + set.size());

        // Iterate over elements
        System.out.println("Set elements:");
        for (String fruit : set) {
            System.out.println(fruit);
        }

        // Clear the set
        set.clear();
        System.out.println("Is set empty? " + set.isEmpty());
    }
}

For more: SetInterface.java

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More to Set Implementations :

• HashSet _{HashSetDataStructure.java}

• LinkedHashSet _{LinkedHashSetDataStructure.java}

• TreeSet _{TreeSetDataStructure.java}