The for-each Loop in Java – Java中的for-each循环

最后修改: 2022年 3月 27日

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:

Java中简单的for loop本质上有三个部分–初始化、boolean条件& 步骤:

for (initialization; boolean-condition; step) {

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

3.for-each 循环

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

for-each循环是在Java 5中引入的。我们也称它为增强型for循环。

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.

这是一种替代性的遍历技术,专门用于遍历数组或集合。值得注意的是,它也使用了for a关键字。但是,我们没有使用循环计数器变量,而是分配了一个与数组或集合类型相同的变量。

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


3.1. Syntax

3.1 语法

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.

对于每一次迭代,for-each 循环会获取集合中的每个元素,并将其存储在一个循环变量中。因此,它为数组或集合的每个元素执行写在循环主体中的代码。

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();

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:

此外,我们还可以使用for-each循环来遍历Map<K, V>

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()) {
      "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(

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.


3.4. Pros and Cons


The for-each loop is one of the important features introduced in Java 5. However, it also has its own benefits and drawbacks.

for-each循环是Java 5中引入的重要功能之一。然而,它也有自己的好处和缺点。

The benefits of the for-each loop are:


  • It helps us avoid programming errors.
  • It makes the code precise and readable.
  • It’s easier to implement.
  • It avoids the chance of an infinite loop.

Because of these benefits, we prefer the for-each loop over the for loop, especially while working with arrays or collections.


The drawbacks of the for-each loop are:


  • We can’t jump over an element as it traverses through each element.
  • Traversing in reverse order is not possible.
  • We can’t modify the array if we’re using a for-each loop.
  • It’s not possible to keep track of the index.
  • It has some performance overhead over the for a loop.

4. Conclusion


In this article, we explored the for-each loop in Java along with its syntax, working, and examples. Finally, we saw its benefits and drawbacks.


As always, the code for these examples is available over on GitHub.