Implementing Associate Array in Java

An associative array stores the set of elements in the form of (key, value) pairs. An associative array is a collection of unique keys and collections of values where each key is associated with one value.

An associate array is an abstract datatype like a map that is composed of a (key, value) pair, such that each key-value appears at most once in the collection. Basically, an array with named indexes is known as an associative array or hashes.

In Java, it is difficult to form the associative array however this could easily be achieved using a HashMap:

Syntax:

Map<String, String> map = new HashMap<String, String>();

// method to add the key,value pair in hashmap
map.put("geeks", "course");
map.put("name", "geeks");


// method to get the value
map.get("name"); // returns "geeks"

Steps to implement the Associative array or associative the List Array using the Map Function :

1. First initialize the map

Map<String ,String> map = new HashMap<>();

2. Then Put the Key, Value to the map using put method

map.put("geeks","Course");

3. After putting all Key Value to the map Convert the map to set using the entrySet() Method

Set<Map.Entry<String ,String> > set = map.entrySet();

4. Then Now convert the set to the List Array using the function ;

List<Map.Entry<String ,String>> list=new ArrayList<>(set);

Implementation of associate array:

Java

// Java program to implement the associate array

import java.io.*;
import java.util.*;

class GFG {

    public static void main(String[] args)
    {

        // Forming the map
        Map<String, String> map = new HashMap<>();

        // method to store the value and
        // key into the map
        map.put("name", "rohit");
        map.put("geeks", "course");
        map.put("India Capital", "Delhi");

        System.out.println(map.size());

        Set<Map.Entry<String, String> > set
                           = map.entrySet();

        List<Map.Entry<String, String> > list
                        = new ArrayList<>(set);

        for (int i = 0; i < list.size(); i++)
        {
            System.out.println(list.get(i).getKey() + ": "
                               + list.get(i).getValue());
        }
    }
}

Output

3
India Capital: Delhi
geeks: course
name: rohit

• Time Complexity: O(n)
• Space Complexity: O(n)

We can iterate through the array using the iterator() method

Syntax:

Iterator it = map.entrySet().iterator();

Java

// Java program to implement the associate array
// and iterate it using iterator() method

import java.io.*;
import java.util.*;
class GFG {
    public static void main(String[] args)
    {
        // Forming the map
        Map<String, Integer> map = new HashMap<>();

        // method to store the put the value and
        // key into the map
        map.put("Roll no", 45);
        map.put("Total Question", 113);
        map.put("Marks ", 400);

        // method to access the value based on
        // the key
        System.out.println(map.size());

        Set<Map.Entry<String, Integer> > set
            = map.entrySet();

        List<Map.Entry<String, Integer> > list
            = new ArrayList<>(set);

        // using the iterator
        Iterator it = list.iterator();
        while (it.hasNext()) {
            System.out.println(it.next());
        }
    }
}

Output

3
Total Question=113
Roll no=45
Marks =400

• Time Complexity: O(n)
• Space Complexity: O(n)