Let's look at three fundamental collection types:

List

List is an ordered collection that allows duplicate elements. It's like a todo list where you can have multiple identical tasks.

import java.util.*;

public class ListExample {
    public static void main(String[] args) {
        List<String> fruits = new ArrayList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Cherry");
        fruits.add("Banana");  // Duplicate allowed

        System.out.println("Fruits: " + fruits);
        System.out.println("Second fruit: " + fruits.get(1));
        
        fruits.remove("Banana");  // Removes the first occurrence
        System.out.println("After removing Banana: " + fruits);
    }
}

Set

Set is a collection that does not allow duplicate elements. It's like a basket of unique marbles.

import java.util.*;

public class SetExample {
    public static void main(String[] args) {
        Set<Integer> numbers = new HashSet<>();
        numbers.add(1);
        numbers.add(2);
        numbers.add(3);
        numbers.add(2);  // This won't be added as it's a duplicate

        System.out.println("Numbers: " + numbers);
        System.out.println("Contains 2? " + numbers.contains(2));
        
        numbers.remove(3);
        System.out.println("After removing 3: " + numbers);
    }
}

Map

Map is a collection of key-value pairs. It's like a dictionary where each word (key) has a definition (value).

import java.util.*;

public class MapExample {
    public static void main(String[] args) {
        Map<String, Integer> ages = new HashMap<>();
        ages.put("Alice", 25);
        ages.put("Bob", 30);
        ages.put("Charlie", 35);

        System.out.println("Ages: " + ages);
        System.out.println("Bob's age: " + ages.get("Bob"));
        
        ages.remove("Alice");
        System.out.println("After removing Alice: " + ages);
        
        for (Map.Entry<String, Integer> entry : ages.entrySet()) {
            System.out.println(entry.getKey() + " is " + entry.getValue() + " years old");
        }
    }
}