Map Data Structure Tutorial

On By monigarrIn algorithm design, java, tutorial

What are Map Data Structures?

The Map interface maps unique keys to values. The key is an object we use to retrieve a value.The Dictionary class defined a data structure for mapping keys to values. It was most useful when we wanted to access data with a specific key instead of an integer index. It’s an obsolete class now and the Map interface is used to obtain key/value storage features.

How & Why use Map Data Structures?

  • Store the value of a key in a Map object, to be retrieved later with it’s key.
  • When no items are found in the Map, several methods throw a NoSuchElementException.
  • ClassCastException is thrown when an object is incompatible with the map elements.
  • If null is not allowed in the map and we attempt to use a null object, a NullPointerException is thrown.
  • If we try to change a unmodifiable map, an UnsupportedOoperationException is thrown.

Code sample to show map functionality with HashMap class:

import java.util.*;
public class MapDemo {
   public static void main(String[] args) {
     Map map1 = new HashMap();
     map1.put("Monica", "5");
     map1.put("Walter", "8");
     map1.put("Isaac","7");
     map1.put("Leola","3");
     System.out.println();
     System.out.println(" Map Elements ");
     System.out.print("t" + map1);
   }
}

Code Output:

Map Elements
     {Walter=8, Isaac=7, Leola=3, Monica=5}

References