How to use a for-each loop in Java? (with Examples)
Java的for-each循环用于简化遍历数组和Iterable集合，语法为for(Type var : collectionOrArray)，支持读取但不支持修改元素、获取索引或并发修改。
In Java, a for-each loop (also called the enhanced for loop) simplifies iterating over arrays and collections without managing indices or iterators manually. It’s cleaner and less error-prone than traditional for loops — as long as you only need to read elements, not modify them or access their positions.
Basic syntax and structure
The for-each loop follows this pattern:
for (Type variable : collectionOrArray) {// use 'variable' here
}
Replace Type with the element type (e.g., String, int), variable with a name of your choice, and collectionOrArray with any array or object that implements Iterable (like ArrayList, HashSet, or String[]).
Iterating over an array
You can loop through any array — primitive or object — using for-each:
String[] names = {"Alice", "Bob", "Charlie"};for (String name : names) {
System.out.println(name);
}
This prints each name on a new line. No index, no length check — just direct access to each element.
- Works with int[], double[], etc., using matching types like int or double
- Cannot get the current index or modify the array (e.g., name = "New" reassigns the local variable, not the array element)
Looping through a Collection
For ArrayList, LinkedList, HashSet, or any Iterable:
Listfor (Integer num : numbers) {
System.out.println(num * 2);
}
This doubles and prints each number. The loop works because List implements Iterable.
- Safe for null collections? No — it throws NullPointerException if the collection reference is null
- Don’t remove elements during iteration — it causes ConcurrentModificationException. Use an explicit Iterator instead
When not to use for-each
Stick with a regular for loop or iterator when you need to:
- Modify the underlying collection (e.g., remove items)
- Access the index (e.g., “process element at position i”)
- Iterate over multiple collections in parallel
- Step by more than one (e.g., skip every other element)
For those cases, the classic for (int i = 0; i or Iterator remains the right tool.
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