programming-examples/java/Data_Structures/Java Program to Implement Hash Tables.java

/*This is a Java Program to implement hash tables. A hash table (also hash map) is a data structure used to implement an associative array, a structure that can map keys to values. A hash table uses a hash function to compute an index into an array of buckets or slots, from which the correct value can be found.*/

/**
 * Java program to implement Hash Table
 **/

import java.util.Scanner;

class HashTable
{
    int[] arr;
    int capacity;

    /** constructor **/
    public HashTable(int capacity)
    {
        this.capacity = nextPrime(capacity);
        arr = new int[this.capacity];
    }

    /** function to insert **/
    public void insert(int ele)
    {
        arr[ele % capacity] = ele;
    }

    /** function to clear **/
    public void clear()
    {
        arr = new int[capacity];
    }

    /** function contains **/
    public boolean contains(int ele)
    {
        return arr[ele % capacity] == ele;
    }

    /** function to delete **/
    public void delete(int ele)
    {
        if (arr[ele % capacity] == ele)
            arr[ele % capacity] = 0;
        else
            System.out.println("\nError : Element not found\n");
    }

    /** Function to generate next prime number >= n **/
    private static int nextPrime( int n )
    {
        if (n % 2 == 0)
            n++;
        for (; !isPrime(n); n += 2);
        return n;
    }

    /** Function to check if given number is prime **/
    private static boolean isPrime(int n)
    {
        if (n == 2 || n == 3)
            return true;
        if (n == 1 || n % 2 == 0)
            return false;
        for (int i = 3; i * i <= n; i += 2)
            if (n % i == 0)
                return false;
        return true;
    }

    /** function to print hash table **/
    public void printTable()
    {
        System.out.print("\nHash Table = ");
        for (int i = 0; i < capacity; i++)
            System.out.print(arr[i] +" ");
        System.out.println();
    }
}

/** Class HashTableTest **/
public class HashTableTest
{
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        System.out.println("Hash Table Test\n\n");
        System.out.println("Enter size");
        /** Make object of HashTable **/
        HashTable ht = new HashTable(scan.nextInt() );
        char ch;
        /**  Perform HashTable operations  **/
        do
            {
                System.out.println("\nHash Table Operations\n");
                System.out.println("1. insert ");
                System.out.println("2. remove");
                System.out.println("3. contains");
                System.out.println("4. clear");
                int choice = scan.nextInt();
                switch (choice)
                    {
                    case 1 :
                        System.out.println("Enter integer element to insert");
                        ht.insert( scan.nextInt() );
                        break;
                    case 2 :
                        System.out.println("Enter integer element to delete");
                        ht.delete( scan.nextInt() );
                        break;
                    case 3 :
                        System.out.println("Enter integer element to check if present");
                        System.out.println("Contains : "+ ht.contains(scan.nextInt() ));
                        break;
                    case 4 :
                        ht.clear();
                        System.out.println("Hash Table Cleared\n");
                        break;
                    default :
                        System.out.println("Wrong Entry \n ");
                        break;
                    }
                /** Display hash table **/
                ht.printTable();
                System.out.println("\nDo you want to continue (Type y or n) \n");
                ch = scan.next().charAt(0);
            }
        while (ch == 'Y'|| ch == 'y');
    }
}

/*

Enter size
10

Hash Table Operations

1. insert
2. remove
3. contains
4. clear
1
Enter integer element to insert
28

Hash Table = 0 0 0 0 0 0 28 0 0 0 0

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. contains
4. clear
1
Enter integer element to insert
24

Hash Table = 0 0 24 0 0 0 28 0 0 0 0

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. contains
4. clear
1
Enter integer element to insert
14

Hash Table = 0 0 24 14 0 0 28 0 0 0 0

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. contains
4. clear
1
Enter integer element to insert
19

Hash Table = 0 0 24 14 0 0 28 0 19 0 0

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. contains
4. clear
1
Enter integer element to insert
94

Hash Table = 0 0 24 14 0 0 94 0 19 0 0

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. contains
4. clear
1
Enter integer element to insert
17

Hash Table = 0 0 24 14 0 0 17 0 19 0 0

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. contains
4. clear
3
Enter integer element to check if present
94
Contains : false

Hash Table = 0 0 24 14 0 0 17 0 19 0 0

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. contains
4. clear
3
Enter integer element to check if present
17
Contains : true

Hash Table = 0 0 24 14 0 0 17 0 19 0 0

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. contains
4. clear
2
Enter integer element to delete
17

Hash Table = 0 0 24 14 0 0 0 0 19 0 0

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. contains
4. clear
1
Enter integer element to insert
94

Hash Table = 0 0 24 14 0 0 94 0 19 0 0

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. contains
4. clear
4
Hash Table Cleared


Hash Table = 0 0 0 0 0 0 0 0 0 0 0

Do you want to continue (Type y or n)

n