Problem : Create a dynamic HashMap that contains key-value pairs.

Program :

Step 1 - Coding

Create a text file c:\sunilos\TestHashMap.java  and copy below contents.

import java.util.*;

/*
 * A program of HashMap.
 */

public class TestHashMap {

    public static void main(String[] args) {

        HashMap hMap = new HashMap();

        // Below HashMap contains RollNo and their respective marks

        hMap.put("RN1001", new Integer(890));
        hMap.put("RN1002", new Integer(900));
        hMap.put("RN1003", new Integer(780));
        hMap.put("RN1004", new Integer(950));

        /*
         * You can insert any object in the HashMap. Primitive data type need to
         * be converted into Objects before inserting.
         */


        // Display the size of Map
        System.out.println("Size of Map is " + hMap.size());

        Object obj = hMap.get("RN1002");
        // Display the value of given key
        System.out.println("Value of Index # = " + obj);


        // Remove the value of given key
        System.out.println("Remove the value of given key "
                + hMap.remove("RN1002"));

         // Will remove all elements
        hMap.clear();

        // Show that HashMap is Empty or not
        System.out.println("Is Empty :-" + hMap.isEmpty());

    }

}

Step 2 - Deployment

1. Create a folder 'c:\sunilos'. 
2. Create or copy TestHashMap.java  into 'c:\sunilos' folder.
3. Open your command prompt and go to  'c:\sunilos'
   
4. Compile TestHashMap.java with help of 
• javac TestHashMap.java command. Compiled class file will be created in the same folder
  
5. Congratulations!! your Java program is ready to serve.

Step 3 - Testing

1. Make sure you are on Command Prompt under c:\sunilos directory
   
2. Now start your java program from command prompt with help of 
• java TestHashMap command.

Output

Size of Map is 4
Value of Index # = 900
Remove the value of given key 900
Is Empty :-true


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