Solved: hashmap print keys and values

In the world of Java programming, the **HashMap** class is a fundamental part of the Java Collections Framework. This versatile class stores elements in mapping relationships, organizing data based on key-value pairs. These pairs facilitate quick search and retrieval processes, making HashMap a favored choice for many programmers. In this article, we’ll delve deeper into how we can print the keys and values in a HashMap.

The Solution to the Problem

import java.util.HashMap;
import java.util.Map;

public class HashMapDemo {
    public static void main(String[] args) {
        // Create a new HashMap
        HashMap<String, Integer> map = new HashMap<>();

        // Add elements to the HashMap
        map.put("One", 1);
        map.put("Two", 2);
        map.put("Three", 3);

        // Print keys and values
        for (Map.Entry<String, Integer> entry : map.entrySet()) {
            System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
        }
    }
}

Step-by-Step Explanation of the Code

Java’s **HashMap** class allows us to store pairs of elements, with each pair consisting of a key and a value. This form of data organization makes way for rapid and efficient data searches. At its core, HashMap uses a technique known as **”Hashing”**, which translates the stored keys into integer values known as hashes, forming the basis for fast data retrieval.

• First up, we import the required classes, namely the HashMap and the Map class. Following that, we get down to actually creating a map – hence the `HashMap map = new HashMap<>();` snippet. Here, “” denotes the types of keys and values we’ll be working with.
• Next up, we use the `.put()` method to add pairs to the map. The key “One” is paired with value 1, “Two” with value 2, and “Three” with value 3 – that’s our map filled.
• Lastly, we retrieve and print our keys and values using a for-each loop. Inside this loop, `entry.getKey()` and `entry.getValue()` methods are used to get the keys and values respectively. The system then prints them out.

Understanding HashMap and Map classes

The **HashMap** and **Map** classes form an integral part of Java’s Collections framework. HashMap, which implements the Map interface, is a part of java.util package. It provides the basic implementation of the Map interface of Java, storing the map in key-value pairs, us hashing for storing the keys.

As for the **Map.Entry** interface, it happens to be a member of the Java Collections Framework. This interface facilitates the manipulation of each key-value pair of entries that feature in a map, enhancing processing efficiency.

Exploring the put() and entrySet() methods

To add elements to a HashMap, we rely upon the **put()** method. The syntax for the same is: `map.put(key, value);`. With a map being an object, the method ‘put()’ is invoked on it by sending the key and the value as arguments.

To print keys and values in a HashMap, we can use the **entrySet()** method in combination with for-each loop. When invoked on a map, ‘entrySet()’ returns a set view consisting of mappings contained in the map. These entries can be iterated using a for-each loop, enabling the HashMap to reveal its keys and values. These iterations are fundamental to instantiating the Map.Entry interface and recovering the keys and values.