Java Program to Implement Associative Array

An associative array stores elements as (key, value) pairs. It is a collection of unique keys, each associated with a specific value. It is also known as a map, is an abstract data type where each key appears at most once in the collection.

In Java, associative arrays can be implemented using the HashMap class, that provides a flexible and efficient way to manage key-value pairs.

Syntax

 
Map<String, String> map = new HashMap<String, String>();
// method to add key-value pairs to the hashmap
map.put("course", "Java");
map.put("author", "John");
// method to get the value associated with a key
map.get("author"); // returns "John"   

Steps to Implement Associative Array

Initialize the Map:

Add Key-Value Pairs:

 
map.put("course", "Java");
map.put("author", "John");   

Convert Map to Set:

Convert Set to List:

File Name: AssociativeArrayExample.java

 
import java.io.*;
import java.util.*;
public class AssociativeArrayExample {
    public static void main(String[] args) {        // Initializing the map
        Map<String, String> map = new HashMap<>();
        // Adding key-value pairs to the map
        map.put("course", "Java");
        map.put("author", "John Doe");
        map.put("language", "English");
        // Printing the size of the map
        System.out.println("Size of map: " + map.size());
        // Converting the map to a set
        Set<Map.Entry<String, String>> set = map.entrySet();
        // Converting the set to a list
        List<Map.Entry<String, String>> list = new ArrayList<>(set);
        // Iterating through the list and printing key-value pairs
        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i).getKey() + ": " + list.get(i).getValue());
        }
    }
}   

Output:

 
Size of map: 3
course: Java
author: John Doe
language: English

Using Iterator

You can also iterate through the associative array using the iterator() method:

File Name: AssociativeArrayWithIterator.java

 
import java.io.*;
import java.util.*;
public class AssociativeArrayWithIterator {
    public static void main(String[] args) {
        // Initializing the map
        Map<String, Integer> map = new HashMap<>();
        // Adding key-value pairs to the map
        map.put("ID", 101);
        map.put("Age", 25);
        map.put("Marks", 90);
        // Printing the size of the map
        System.out.println("Size of map: " + map.size());
        // Converting the map to a set
        Set<Map.Entry<String, Integer>> set = map.entrySet();
        // Converting the set to a list
        List<Map.Entry<String, Integer>> list = new ArrayList<>(set);
        // Using iterator to iterate through the list
        Iterator<Map.Entry<String, Integer>> iterator = list.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }
    }
}   

Output:

 
Size of map: 3
Age=25
ID=101
Marks=90

Conclusion

Implementing an associative array in Java using HashMap is straightforward and efficient. The HashMap class provides various methods to add, retrieve, iterate, and remove key-value pairs, making it a versatile tool for managing collections of data. By following the steps outlined above, you can easily handle associative arrays in your Java programs, allowing for efficient data management and retrieval.

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