We have one more collection, called Map. We will take an example and discuss Map as we proceed with the code. This interface takes the values in the form of a key and value pair. 

We create a class, hashMapexample, and within that the we define HashMap. HashMap requires two types of argument, such as Integer and String:

package coreJava;

import java.util.HashMap;

public class hashMapexample {

    public static void main(String[] args) {

       HashMap<Integer, String> hm= new HashSet<Integer, String>();

    }
}

Here, Integer is the key and String is the value. Now if you type hm. in your IDE, you will see a few methods present in HashMap; let's use the put method:

        hm.put(0, "hello");
        hm.put(1, "goodbye");
        hm.put(2, "morning");
        hm.put(3, "evening");

The put method takes the input in the form of keys and values. Also, the value of the key needs to be an integer, it can be a string as well. The key is just something we define for...