Different Ways to Iterate on Map in Java

Introduction

In this blog, we will explore different ways to iterate over a map in Java, discussing various techniques and code examples. Let's dive in!

1. Iterating using a for-each loop

The for-each loop provides a simple way to iterate over a map. The key-value pairs of the map can be accessed by using the entrySet() method. Here's an illustration:

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

public class IterationWithFor {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();

        map.put("Apple", 10);
        map.put("Banana", 15);
        map.put("Orange", 5);

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

2. Iterating using iterators

Using iterators provides more control over the iteration process. We can obtain an iterator using the entrySet().iterator() method and then iterate using a while loop. Here's an illustration:

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

public class IterationWithIterator {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();

        map.put("Apple", 10);
        map.put("Banana", 5);
        map.put("Orange", 8);

        Iterator<Map.Entry<String, Integer>> iterator = map.entrySet().iterator();

        while (iterator.hasNext()) {
            Map.Entry<String, Integer> entry = iterator.next();

            System.out.println("Key: " + entry.getKey() + ", Value: " entry.getValue());
        }
    }
}

3. Iterating using Java 8 Stream API

We can iterate over a map using streams and lambdas now that Java 8 includes the Stream API. Here's an illustration:

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

public class IterationWithStream {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();

        map.put("Apple", 10);
        map.put("Banana", 5);
        map.put("Orange", 8);

        map.entrySet().stream()
                .forEach(entry -> {
                    System.out.println("Key: " + entry.getKey() + ", Value: " + entry.getValue());
                });
    }
}

4. Iterating over keys or values:

you can also iterate over the keys or values of a map independently, you can use the keySet() or values() methods, respectively. Here are examples for both cases:

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

public class IterationOnKeyValue {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();

        map.put("Apple", 10);
        map.put("Banana", 15);
        map.put("Orange", 5);

        // Iterate over keys
        for (String key : map.keySet()) {
            System.out.println("Key: " + key);
        }

        // Iterate over values
        for (Integer value : map.values()) {
            System.out.println("Value: " + value);
        }
    }
}

Conclusion

In this blog, we explored different ways to iterate on a map: using a for-each loop, iterators, Java 8 Stream API, and iterating over keys or values directly. Each approach has its advantages and can be chosen based on specific requirements.