Iterable Interface in Java

The Iterable interface in Java represents a collection of elements that can be traversed one by one. It allows objects to be iterated using an Iterator, making them compatible with the enhanced for-each loop.

• Introduced in JDK 1.5 and part of java.lang package
• Provides iterator(), spliterator(), and forEach() methods
• Enables use of enhanced for-each loop

Declaration Syntax

public interface Iterable<T>

Here: T represents a generic type parameter in the Iterable interface.

import java.util.*;

public class Test {
    public static void main(String[] args) {
        Iterable<Integer> numbers = Arrays.asList(1, 2, 3, 4);

        for (Integer num : numbers) {
            System.out.println(num);
        }
    }
}

1
2
3
4

Explanation: Here, T is Integer, so the iterable contains integer values and can be used in a for-each loop.

Ways of Iterating

There are three ways in which objects of Iterable can be iterated.

Using enhanced for loop

Objects of Classes implementing Collection interface can be iterated using for-each loop, Collection interface extends Iterable interface.

import java.io.*;
import java.util.*;

class IterateUsingEnhancedForLoop {
    public static void main (String[] args) {
        
      // create a list
      List<String> list = new ArrayList<String>();

      // add elements
      list.add("Geeks");
      list.add("for");
      list.add("Geeks");

      // Iterate through the list
      for( String element : list ){
          System.out.println( element );
      }
    }
}

Geeks
for
Geeks

Using forEach loop

The forEach() method takes the Lambda Expression as a parameter. This Lambda Expression is called for each element of the collection. In the below example, for each element of the list, the function prints the element to the console.

import java.io.*;
import java.util.*;

class IterateUsingforEach {
    public static void main(String[] args)
    {
          // create a list
        List<String> list = new ArrayList<>();

          // add elements to the list
        list.add("Geeks");
        list.add("for");
        list.add("Geeks");

          // Iterate through the list
        list.forEach(
            (element) -> { System.out.println(element); });
    }
}

Geeks
for
Geeks

Using Iterator

We can iterate the elements of Java Iterable by obtaining the Iterator from it using the iterator() method. The methods used while traversing the collections using Iterator to perform the operations are:

• hasNext(): It returns false if we have reached the end of the collection, otherwise returns true.
• next(): Returns the next element in a collection.
• remove(): Removes the last element returned by the iterator from the collection.
• forEachRemaining(): Performs the given action for each remaining element in a collection, in sequential order.

import java.io.*;
import java.util.*;

class IterateUsingIterator {
    public static void main(String[] args)
    {
        List<String> list = new ArrayList<>();

        list.add("Geeks");
        list.add("for");
        list.add("Geeks");

        Iterator<String> iterator = list.iterator();

        while (iterator.hasNext()) {
            String element = iterator.next();
            System.out.println(element);
        }
    }
}

Geeks
for
Geeks

Methods of Iterable

Related topics

• Implementing Iterator and Iterable Interface
• Iterators in Java