collections

Java Collections Framework

Java Collections Framework

The Java Collections Framework provides a set of interfaces and classes for working with groups of objects. It includes lists, sets, and maps, which are commonly used to store and manipulate data.

List Interface

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

public class CollectionsExample {
    public static void main(String[] args) {
        List names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");

        System.out.println("Names List: " + names);
    }
}

The List interface is used to store ordered collections. The ArrayList class is one of the implementations of the List interface, which allows dynamic resizing.

Set Interface

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

public class CollectionsExample {
    public static void main(String[] args) {
        Set uniqueNames = new HashSet<>();
        uniqueNames.add("Alice");
        uniqueNames.add("Bob");
        uniqueNames.add("Alice");  // Duplicate value

        System.out.println("Unique Names Set: " + uniqueNames);
    }
}

The Set interface is used to store unique elements. The HashSet class is one of the implementations, and it automatically removes duplicates from the collection.

Map Interface

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

public class CollectionsExample {
    public static void main(String[] args) {
        Map phoneBook = new HashMap<>();
        phoneBook.put("Alice", 12345);
        phoneBook.put("Bob", 67890);

        System.out.println("Phone Book: " + phoneBook);
    }
}

The Map interface stores key-value pairs. In this example, a HashMap is used to associate names with phone numbers.