Java: Collection Framework Overview

Collection (interface)
├── List (interface) — Ordered, allows duplicates
│   ├── ArrayList (implementation)
│   ├── LinkedList (implementation)
│   └── Vector (implementation)
├── Set (interface) — Unordered, no duplicates
│   ├── HashSet (implementation)
│   ├── TreeSet (implementation)
│   └── LinkedHashSet (implementation)
└── Queue (interface) — Queue
    ├── LinkedList (implementation)
    └── PriorityQueue (implementation)

Map (interface) — Key-value pairs
├── HashMap (implementation)
├── TreeMap (implementation)
├── LinkedHashMap (implementation)
└── Hashtable (implementation)

import java.util.ArrayList;
import java.util.Collection;

public class CollectionDemo {
    public static void main(String[] args) {
        Collection<String> collection = new ArrayList<>();
        
        // Add elements
        collection.add("Alice");
        collection.add("Bob");
        collection.add("Charlie");
        System.out.println("Collection: " + collection);  // [Alice, Bob, Charlie]
        
        // Check
        System.out.println("Contains Alice: " + collection.contains("Alice"));  // true
        System.out.println("Size: " + collection.size());  // 3
        System.out.println("Is empty: " + collection.isEmpty());  // false
        
        // Remove
        collection.remove("Bob");
        System.out.println("After remove: " + collection);  // [Alice, Charlie]
        
        // Convert to array
        Object[] array = collection.toArray();
        for (Object obj : array) {
            System.out.println(obj);
        }
        
        // Clear
        collection.clear();
        System.out.println("After clear, size: " + collection.size());  // 0
    }
}

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

public class IteratorDemo {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");
        
        // Method 1: for-each
        for (String name : names) {
            System.out.println(name);
        }
        
        // Method 2: Iterator
        Iterator<String> it = names.iterator();
        while (it.hasNext()) {
            String name = it.next();
            System.out.println(name);
        }
        
        // Method 3: Remove with Iterator
        Iterator<String> it2 = names.iterator();
        while (it2.hasNext()) {
            String name = it2.next();
            if (name.startsWith("B")) {
                it2.remove();  // Safe removal
            }
        }
        System.out.println("After remove: " + names);  // [Alice, Charlie]
    }
}