Uses of Collections in Java

In Java, collections can be defined as a framework that is used for storing and manipulating a set of objects. Collections have an important role of managing and organizing set of objects in Java. Let's understand in detail about the uses and benefits of collections in Java.

Collections in Java

In Java, the work Collections can be defined as a Java framework which consists a set of classes and interfaces that are provided and stored in the java.util package in Java. The collections framework is provided for representing and manipulating a set of objects in Java. The main purpose of introducing the Collections framework in Java was to standardize the manner in which collections were handled in Java and provide a unified system for several data structures.

A set of interfaces such as List, Set, Queue, Map including their implementation classes are provided in the Collections framework for the purpose of addressing several needs regarding storage, retrieval, and manipulation of data and objects in Java.

Let us understand about Collections in Java with the help of a Java example program.

Filename: JavaCollections.java

import java.util.*;
class Person implements Comparable<Person> {
    private String name;
    private int age;
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
    @Override
    public int compareTo(Person otherPerson) {
        return Integer.compare(this.age, otherPerson.age);
    }
}
public class JavaCollections {
    public static void main(String[] args) {
        // Demonstrating Sublist
        List<Integer> originalList = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10));
        List<Integer> subList = originalList.subList(2, 7);
        System.out.println("Original List: " + originalList);
        System.out.println("Sublist (from index 2 to 6): " + subList);

        // Demonstrating Binary Search
        Collections.sort(originalList);
        int key = 7;
        int index = Collections.binarySearch(originalList, key);
        System.out.println("Sorted List: " + originalList);
        System.out.println("Binary Search for " + key + ": Found at index " + index);
        // Demonstrating Arrays.asList() for Creating List from Array
        String[] stringArray = { "Java", "Python", "C++" };
        List<String> stringList = new ArrayList<>(Arrays.asList(stringArray));
        System.out.println("List from Array: " + stringList);
        // Demonstrating Collection.toArray() for Converting List to Array
        String[] toArray = stringList.toArray(new String[0]);
        System.out.println("Array from List: " + Arrays.toString(toArray));
        // Demonstrating Collections.nCopies() for Creating Immutable List
        List<String> immutableList = Collections.nCopies(3, "Immutable");
        System.out.println("Immutable List: " + immutableList);
    }
}

Output:

Original List: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Sublist (from index 2 to 6): [3, 4, 5, 6, 7]
Sorted List: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Binary Search for 7: Found at index 6
List from Array: [Java, Python, C++]
Array from List: [Java, Python, C++]
Immutable List: [Immutable, Immutable, Immutable]

Let's now understand about the uses and benefits of Collections in Java in detail.

Uses of Collections in Java

There are several benefits and uses of Collections in Java and let us discuss each one of them in detail in the following paragraphs.

One of the major uses of collections in Java is storing and organizing data and information in a pattern which is both flexible and dynamic. There are various interfaces provided in the Collections framework such as List, Set, Map, and each interface provides a functionality for storing and retrieving information, data, and elements.
Another major use of Collections in Java is that they are utilized in making the iteration process simple in Java. Also, the process of traversing through a set or group of objects is made simpler and faster with the help of Collections. Iterators which are provided by the Collections framework is utilized for providing a standard way for navigating through several elements, regardless of the type of the collection.
Another important use of Collections in Java is to provide the implementation of the algorithms that are utilized for manipulating and processing data. Utility classes are also included in the Collections framework of Java and it is present in the util package, such as Collections and Arrays, which are utilized for providing methods that can be used for sorting, searching, and various other operations.
Another major use and advantage of using Collections framework in Java is that it can be used for enhancing the reusability of the Java code and its maintainability. With the help of interfaces and their implementation classes that are available in the Collections Framework, users are provided the functionality of creating code that is both flexible and generic and that can be adapted to several types of collections. This feature is used for enabling the development of the software that is both modular and scalable.

Let's understand about Collections Framework in Java in detail with the help of a Java example program.

Filename: CollectoinsFramework.java

import java.io.*;
import java.util.*;
public class CollectoinsFramework {
    public static void main(String[] args) {
        // List Example
        List<String> list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        list.add("Orange");
        System.out.println("List Example:");
        iterateAndPrint(list);
        // Set Example
        Set<Integer> set = new HashSet<>();
        set.add(10);
        set.add(20);
        set.add(30);
        System.out.println("\nSet Example:");
        iterateAndPrint(set);
        // Map Example with LinkedHashMap
        Map<String, Integer> linkedHashMap = new LinkedHashMap<>();
        linkedHashMap.put("One", 1);
        linkedHashMap.put("Two", 2);
        linkedHashMap.put("Three", 3);
        System.out.println("\nLinkedHashMap Example:");
        iterateAndPrint(linkedHashMap.entrySet());
        // Creating an Unmodifiable Collection
        Collection<String> unmodifiableCollection = Collections.unmodifiableCollection(list);
        System.out.println("\nUnmodifiable Collection Example:");
        iterateAndPrint(unmodifiableCollection);
        // Serialization Example with a Map
        serializeAndDeserializeMap(linkedHashMap);
    }
    private static <T> void iterateAndPrint(Collection<T> collection) {
        for (T element : collection) {
            System.out.print(element + " ");
        }
        System.out.println();
    }
    private static void serializeAndDeserializeMap(Map<String, Integer> map) {
        try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("serializedMap.ser"));
                ObjectInputStream ois = new ObjectInputStream(new FileInputStream("serializedMap.ser"))) {
            // Serialize the Map
            oos.writeObject(map);
            System.out.println("\nMap Serialized Successfully.");
            // Deserialize the Map
            Map<String, Integer> deserializedMap = (Map<String, Integer>) ois.readObject();
            System.out.println("Map Deserialized Successfully:");
            iterateAndPrint(deserializedMap.entrySet());
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

Output:

List Example:
Apple Banana Orange
Set Example:
20 10 30
LinkedHashMap Example:
One=1 Two=2 Three=3
Unmodifiable Collection Example:
Apple Banana Orange
Map Serialized Successfully.
Map Deserialized Successfully:
One=1 Two=2 Three=3

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