Create an ArrayList, HashSet, and HashMap, and perform basic operations like adding, removing, and iterating.

Here’s how to create an ArrayList, HashSet, and HashMap in Java and perform basic operations such as adding, removing, and iterating through them.

1. ArrayList Example

import java.util.ArrayList;

public class ArrayListExample {
    public static void main(String[] args) {
        // Create an ArrayList
        ArrayList<String> fruits = new ArrayList<>();

        // Add elements to the ArrayList
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Orange");

        // Iterate over the ArrayList
        System.out.println("ArrayList Elements:");
        for (String fruit : fruits) {
            System.out.println(fruit);
        }

        // Remove an element from the ArrayList
        fruits.remove("Banana");
        System.out.println("After removing 'Banana': " + fruits);

        // Accessing element by index
        System.out.println("Element at index 1: " + fruits.get(1));
    }
}

2. HashSet Example

import java.util.HashSet;

public class HashSetExample {
    public static void main(String[] args) {
        // Create a HashSet
        HashSet<String> fruits = new HashSet<>();

        // Add elements to the HashSet
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Orange");
        fruits.add("Apple"); // Duplicate entry (will be ignored)

        // Iterate over the HashSet
        System.out.println("HashSet Elements:");
        for (String fruit : fruits) {
            System.out.println(fruit);
        }

        // Remove an element from the HashSet
        fruits.remove("Banana");
        System.out.println("After removing 'Banana': " + fruits);

        // Check if a value exists
        System.out.println("Contains 'Apple'? " + fruits.contains("Apple"));
    }
}

3. HashMap Example

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

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

        // Add key-value pairs to the HashMap
        fruitPrices.put("Apple", 100);
        fruitPrices.put("Banana", 40);
        fruitPrices.put("Orange", 80);

        // Iterate over the HashMap
        System.out.println("HashMap Elements:");
        for (Map.Entry<String, Integer> entry : fruitPrices.entrySet()) {
            System.out.println(entry.getKey() + " costs " + entry.getValue() + " units");
        }

        // Remove an element from the HashMap
        fruitPrices.remove("Banana");
        System.out.println("After removing 'Banana': " + fruitPrices);

        // Check if a key exists
        System.out.println("Contains 'Apple'? " + fruitPrices.containsKey("Apple"));
    }
}

Key Points:

ArrayList:
- Stores elements in the order they are added.
- Allows duplicate elements.
- Provides indexed access to elements.
HashSet:
- Does not allow duplicate elements.
- Does not guarantee the order of elements.
HashMap:
- Stores key-value pairs.
- Does not allow duplicate keys, but values can be duplicated.
- Efficient for searching, adding, and removing elements using keys.