What is HashMap and HashTable in Java and Sample Program

Map Key Features 

• Map does not inherit from the Collection interface. 
• Map doesn't allow duplicate keys, but you can have duplicate values
• Key-Value Pair Storage: Maps store data as key-value pairs.
• Unique Keys: Each key in a map must be unique, although multiple keys can map to the same value.
• Null Handling: Some implementations allow null keys and/or values, while others do not.

What is HashMap 

• Uses a hash table to store the mappings.
• Allows one null key and multiple null values.
• Does not maintain any specific order of the keys.
• Not synchronized, making it suitable for single-threaded use.
• Use Case: When you don’t need sorted keys or thread safety, and you need efficient lookups and insertions.
•  Primary operations you can perform on the maps in Java are:
• Adding elements
• Removing elements
• Changing elements
• Iterating through the map

package com.example;

import java.util.HashMap;
import java.util.Map;

public class HashMapExample {
    public static void main(String[] args) {
        HashMap<Integer,String> map=new HashMap<Integer,String>();//Creating HashMap
        map.put(1,"Mango");  //Put elements in Map
        map.put(2,"Apple");
        map.put(3,"Banana");
        map.put(1,"Grapes"); //trying duplicate key

        System.out.println("Iterating Hashmap...");
        for(Map.Entry m : map.entrySet()){
            System.out.println(m.getKey()+" "+m.getValue());
        }
    }
}

What is HashTable

• Uses a hash table to store the mappings.
• Allows one null key and multiple null values.
• Does not maintain any specific order of the keys.
• Not synchronized, making it suitable for single-threaded use.
• Use Case: When you don’t need sorted keys or thread safety, and you need efficient lookups and insertions.
• Primary operations you can perform on the maps in Java are:
• Adding elements
• Removing elements
• Changing elements
• Iterating through the map

package com.example;

import java.util.Hashtable;
import java.util.Map;

public class HashTableExample {
    public static void main(String[] args) {
        Hashtable<Integer,String> hm=new Hashtable<Integer,String>();

        hm.put(100,"Amit");
        hm.put(102,"Ravi");
        hm.put(101,"Vijay");
        hm.put(103,"Rahul");

        for(Map.Entry m:hm.entrySet()){
            System.out.println(m.getKey()+" "+m.getValue());
        }
    }
}