List, Set, and Map in Java

Category : Java | Sub Category : Java.util Package | By Prasad Bonam Last updated: 2023-07-12 11:03:50 Viewed : 550

Here are examples of using List, Set, and Map in Java:

List Example:

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import java.util.ArrayList;
import java.util.List;

public class ListExample {
    public static void main(String[] args) {
        // Create a List of strings
        List<String> names = new ArrayList<>();

        // Add elements to the List
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");

        // Access elements by index
        System.out.println("Element at index 0: " + names.get(0));

        // Update elements
        names.set(1, "Brian");
        System.out.println("Updated element at index 1: " + names.get(1));

        // Remove elements
        names.remove(2);
        System.out.println("Size after removing an element: " + names.size());

        // Iterate over the List
        System.out.println("Elements in the List:");
        for (String name : names) {
            System.out.println(name);
        }
    }
}

Set Example:

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import java.util.HashSet;
import java.util.Set;

public class SetExample {
    public static void main(String[] args) {
        // Create a Set of integers
        Set<Integer> numbers = new HashSet<>();

        // Add elements to the Set
        numbers.add(10);
        numbers.add(20);
        numbers.add(30);
        numbers.add(20); // Adding a duplicate element, which will be ignored

        // Access elements (no specific order in Set)
        System.out.println("Size of the Set: " + numbers.size());
        System.out.println("Is 20 present in the Set? " + numbers.contains(20));

        // Remove elements
        numbers.remove(10);
        System.out.println("Size after removing an element: " + numbers.size());

        // Iterate over the Set
        System.out.println("Elements in the Set:");
        for (int number : numbers) {
            System.out.println(number);
        }
    }
}

Map Example:

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

public class MapExample {
    public static void main(String[] args) {
        // Create a Map of names and ages
        Map<String, Integer> ageMap = new HashMap<>();

        // Add key-value pairs to the Map
        ageMap.put("Alice", 25);
        ageMap.put("Bob", 30);
        ageMap.put("Charlie", 35);

        // Access values by key
        System.out.println("Age of Bob: " + ageMap.get("Bob"));

        // Update values
        ageMap.put("Bob", 32);
        System.out.println("Updated age of Bob: " + ageMap.get("Bob"));

        // Remove key-value pairs
        ageMap.remove("Charlie");
        System.out.println("Size after removing an element: " + ageMap.size());

        // Iterate over the Map entries
        System.out.println("Elements in the Map:");
        for (Map.Entry<String, Integer> entry : ageMap.entrySet()) {
            System.out.println("Name: " + entry.getKey() + ", Age: " + entry.getValue());
        }
    }
}

In these examples, we create instances of List (using ArrayList), Set (using HashSet), and Map (using HashMap). We perform operations such as adding elements, accessing elements, updating elements, removing elements, and iterating over the collections.

List maintains an ordered collection of elements with possible duplicates, Set stores a unique collection of elements without a specific order, and Map stores key-value pairs. Each collection has its own methods and characteristics for manipulating and accessing data.

You can customize the examples by changing the data types or using different implementations of List, Set, and Map, such as LinkedList, TreeSet, or LinkedHashMap, depending on your requirements.