Java Program to Iterate over a HashMap

In this article, we will understand how to iterate over a HashMap. Java HashMap is a hash table based implementation of Java's Map interface. It is a collection of key-value pairs.

Below is a demonstration of the same −

Suppose our input is −

Input Hashmap: {Java=Enterprise, JavaScript=Frontend, Mysql=Backend, Python=ML/AI}

The desired output would be −

The keys of the Hashmap are: Java, JavaScript, Mysql, Python,
The Values of the Hashmap are: Enterprise, Frontend, Backend, ML/AI,

Algorithm

Step 1 - START
Step 2 - Declare namely
Step 3 - Define the values.
Step 4 - Create a hashmap of strings and initialize elements in it using the ‘put’ method.
Step 5 - Display the hashmap on the console.
Step 6 - Iterate over the elements of the hashmap, and fetch each key using ‘keySet’ method.
Step 7 - Display this on the console.
Step 6 - Stop

Example 1

Here, we bind all the operations together under the ‘main’ function.

import java.util.HashMap;
import java.util.Map.Entry;
public class Demo {
   public static void main(String[] args) {
      System.out.println("The required packages have been imported");
      HashMap<String, String> input_map = new HashMap<>();
      input_map.put("Java", "Enterprise");
      input_map.put("Python", "ML/AI");
      input_map.put("JavaScript", "Frontend");
      input_map.put("Mysql", "Backend");
      System.out.println("The HashMap is defined as: " + input_map);
      System.out.print("\nThe keys of the Hashmap are: ");
      for(String key: input_map.keySet()) {
         System.out.print(key);
         System.out.print(", ");
      }
      System.out.print("\nThe Values of the Hashmap are: ");
      for(String value: input_map.values()) {
         System.out.print(value);
         System.out.print(", ");
      }
   }
}

Output

The required packages have been imported
The HashMap is defined as: {Java=Enterprise, JavaScript=Frontend, Mysql=Backend, Python=ML/AI}

The keys of the Hashmap are: Java, JavaScript, Mysql, Python,
The Values of the Hashmap are: Enterprise, Frontend, Backend, ML/AI,

Example 2

Here, we encapsulate the operations into functions exhibiting object oriented programming.

import java.util.HashMap;
public class Demo {
   static void print_keys(HashMap<String, String> input_map){
      System.out.print("\nThe keys of the Hashmap are: ");
      for(String key: input_map.keySet()) {
         System.out.print(key);
         System.out.print(", ");
      }
   }
   static void print_values( HashMap<String, String> input_map){
      System.out.print("\nThe Values of the Hashmap are: ");
      for(String value: input_map.values()) {
         System.out.print(value);
         System.out.print(", ");
      }
   }
   public static void main(String[] args) {
      System.out.println("The required packages have been imported");
      HashMap<String, String> input_map = new HashMap<>();
      input_map.put("Java", "Enterprise");
      input_map.put("Python", "ML/AI");
      input_map.put("JavaScript", "Frontend");
      input_map.put("Mysql", "Backend");
      System.out.println("The HashMap is defined as: " + input_map);
      print_keys(input_map);
      print_values(input_map);
   }
}

Output

The required packages have been imported
The HashMap is defined as: {Java=Enterprise, JavaScript=Frontend, Mysql=Backend, Python=ML/AI}

The keys of the Hashmap are: Java, JavaScript, Mysql, Python,
The Values of the Hashmap are: Enterprise, Frontend, Backend, ML/AI,