The for-each Loop in Java

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1. Overview

In this tutorial, we’ll discuss the for-each loop in Java along with its syntax, working, and code examples. Finally, we’ll understand its benefits and drawbacks.

2. Simple for Loop

The simple for loop in Java essentially has three parts – initialization, boolean condition & step:

for (initialization; boolean-condition; step) {
    statement;
}

It starts with the initialization of a loop variable, followed by a boolean expression. If the condition is true, it executes the statement(s) in the loop and increments/decrements the loop variable. Otherwise, it terminates the loop.

This pattern makes it slightly complex and difficult to read. Moreover, if we do not write the condition properly, there’s always a chance to get into an infinite loop.

3. for-each Loop

The for-each loop was introduced in Java 5. We also call it an enhanced for loop.

It’s an alternate traversing technique specifically introduced to traverse arrays or collections. Noticeably, it also uses the for a keyword. However, instead of using a loop counter variable, we assign a variable of the same type as that of an array or a collection.

The name for-each signifies that each element of an array or a collection is traversed, one after another.

3.1. Syntax

The for-each loop consists of the declaration of a loop variable followed by a colon (:), which is followed by the name of an array or collection:

for (data_type var_name : array | collection) {
    // code
}

3.2. Working

For each iteration, the for-each loop takes each element of the collection and stores it in a loop variable. Thus, it executes the code written in the body of the loop for each element of the array or collection.

Most importantly, the traversal happens until the last element of the array or collection.

3.3. Examples

Let’s see an example of traversing an array with the for-each loop:

int numbers[] = { 1, 2, 3, 4, 5 };

for (int number : numbers) {
    System.out.print(number + " ");
}

Here, the for-each loop traverses over each element of the array numbers one by one until the end. Therefore, there’s no need to access the array elements using indexing.

Now, let us see some examples of traversing various collections with the for-each loop.

Let’s start with a List:

String[] wordsArray = { "Java ", "is ", "great!" };
List<String> wordsList = Arrays.asList(wordsArray);

for (String word : wordsList) {
    System.out.print(word + " ");
}

Similarly, we can traverse through all the elements of a Set:

Set<String> wordsSet = new HashSet();
wordsSet.addAll(wordsList);

for (String word : wordsSet) {
    System.out.print(word + " ");
}

Additionally, we can also use the for-each loop to traverse through a Map<K, V> as well:

Map<Integer, String> map = new HashMap<>();
map.put(1, "Java");
map.put(2, "is");
map.put(3, "great!");

for (Entry<Integer, String> entry : map.entrySet()) {
    System.out.println(
      "number: " + entry.getKey() +
      " - " +
      "Word: " + entry.getValue());
}

In the same way, we can use a for-each loop to iterate through various other data structures in Java.

However, if the array or collection is null, it throws a NullPointerException:

int[] numbers = null;
for (int number : numbers) {
    System.out.print(number + " ");
}

The above code throws a NullPointerException:

Exception in thread "main" java.lang.NullPointerException
    at com.baeldung.core.controlstructures.loops.ForEachLoop.traverseArray(ForEachLoop.java:63)
    ..

Hence, we must check if the array or collection is null before passing it to the for-each loop.

The for-each loop doesn’t execute at all if the array or collection is empty.