Enhanced for loop in java

We will cover the usage of Enhanced for-loop in this section. This is also referred to as for-each loop. The following code shows how to iterate over the elements in a Collection using the traditional Iterator interface.

ForEachTest.java

package foreach;

import java.util.*;

public class ForEachTest
{
 public static void main(String[] args)
 {
  List numbers = new ArrayList();
  numbers.add(1);numbers.add(2);numbers.add(3);
  
  Iterator numbersIterator = null;
  for(numbersIterator = numbers.iterator(); numbersIterator.hasNext();)
  {
   System.out.println(numbersIterator.next());;
  }
 }
}

Though the goal of the above program is traversing over the elements in the list collection, we are depending on the Iterator API to achieve this. A replacement to the Iterator is the usage of Enhanced for-loop, through which it is possible to have a short and a neat code like this,

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

Let us see how the above syntax is used to traverse over the collection. The expression before the symbol ':' is a declaration statement which declares an Integer object called number for holding the individual element from the collection. The expression that follows after the symbol must be a Collection type whose elements can be iterated. Precisely, this type must implement an interface called java.util.Iterable which has a single method called iterator(). During compile-time, the compiler translates the above code which looks very similar to the following,

Iterator intIterator = numbers.iterator();

for(;intIterator.hasNext();)
{
 System.out.println(intIterator.next());
}

Even it is possible to apply this new syntax for type Arrays. So, the following code is perfectly legal and it compiles fine.

int [] numbers = {10, 20, 30, 40, 50};

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

The enhanced for-loop is just a convenience from the programmer's point of view for iterating over the Collection. But the usage of this loop has some dis-advantages. The first one out of the two is that step-value cannot be incremented. For example, it is not possible to traverse the first element and then the thirth element and so on. And the second dis-advantage is that backward traversal is not possible.