| Criteria | Iterable | Collection |
|---|---|---|
| Package | java.lang | java.util |
| Primary Purpose | To provide a mechanism to iterate over a sequence of elements. | Represents a group of objects and extends Iterable. It’s the root interface for most of the Java Collections Framework. |
| Main Methods | iterator() | add(), remove(), size(), isEmpty(), contains(), clear(), toArray(), and many more, in addition to iterator(). |
| Sub-interfaces/Implementations | None directly, but many classes and interfaces implement Iterable. | Interfaces like Set, List, Queue, etc., and classes like ArrayList, HashSet, LinkedList, and more. |
| Usage | Used when a class wants to allow iteration over its elements, even without being a full-fledged collection. | Used when a class needs to represent and manage a group of elements with standard collection operations. |
| For-each Loop | Any class implementing Iterable can be used with the enhanced for-each loop in Java. | As Collection extends Iterable, any class implementing Collection can be used with the enhanced for-each loop. |
| Thread Safety | Depends on the specific implementation. | Standard implementations like ArrayList and HashSet are not thread-safe. Synchronization must be handled externally if concurrent modifications are expected. |
Example: Difference Between Iterable and Collection in Java
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
public class IterableVsCollectionDemo {
public static void main(String[] args) {
// Create an ArrayList which is a type of Collection
Collection<String> collection = new ArrayList<>();
collection.add("Java");
collection.add("Python");
collection.add("C++");
// Demonstrating Collection methods
System.out.println("Size of collection: " + collection.size());
System.out.println("Is collection empty? " + collection.isEmpty());
// As Collection extends Iterable, it can use the iterator() method
Iterator<String> iterator = collection.iterator();
System.out.print("Iterating over collection: ");
while(iterator.hasNext()) {
System.out.print(iterator.next() + " ");
}
System.out.println();
// Create a simple Iterable
Iterable<String> iterable = new ArrayList<>(collection);
// Iterating using the Iterable
for (String lang : iterable) {
System.out.print(lang + " ");
}
}
}
Output:
Size of collection: 3 Is collection empty? false Iterating over collection: Java Python C++ Java Python C++
Explanation:
1. Iterable: It is an interface in Java that represents a group of objects which one can iterate over. The primary method it provides is iterator(), which returns an Iterator to loop over the elements.
2. Collection: It is also an interface and is a more advanced version of Iterable. Collection extends Iterable and represents a group of objects, with methods for adding, removing, and querying elements. It is the root interface in the collection hierarchy.
3. In the provided example:
– A Collection (ArrayList in this case) is created and populated with some programming languages.
– The size() and isEmpty() methods from the Collection interface are demonstrated.
– The iterator() method from the Iterable interface is used to iterate over the elements of the Collection.- A simple Iterable is created from the Collection and demonstrated.
4. When to use:
– Use Iterable when you only need to provide a way to iterate over elements.
– Use Collection when you need advanced operations like adding, removing, or querying elements.
In summary, Iterable is a base interface for any class that can be iterated over, while Collection provides more advanced capabilities and serves as the root for the Java collections framework.