Array Traversals

Vocabulary

English	Meaning
traversal/træˈvɜːsl/	The foundation of every array algorithm.
enhanced for loop/enˈhænst fɔː luːp/	enhanced for loop

Visiting every element

A traversal 遍历 visits every element of an array, usually in order.
The standard indexed loop: for (int i = 0; i < a.length; i++) { ... a[i] ... }
i steps from 0 to length - 1, so a[i] reaches each element once.
Traversal is the foundation of every array algorithm.

The for-each loop

The enhanced for loop (for-each) 增强for循环 visits each value without an index:
for (int x : a) { ... x ... } — x takes each element's value in turn.
Cleaner when you only need the values, not their positions.
But it can't change the array or use the index.

Traversing an array with an indexed for loop or an enhanced for loop

Indexed vs. for-each

Use the indexed loop when you need the position i, or to modify elements.
Use the for-each loop when you just need to read each value.
a[i] = 0; needs the indexed loop; summing values can use for-each.
Both visit every element — pick the one that fits the task.

Bounds again

The indexed loop's condition i < a.length keeps i valid.
i <= a.length overruns by one → ArrayIndexOutOfBoundsException.
The for-each loop can't go out of bounds — it handles the range for you.
When you write the index yourself, you own the bounds.

Watch out

The for-each loop reads values but can't assign back into the array. for (int x : a) { x = 0; } changes only the local copy x, not a — to zero out the array you need the indexed loop a[i] = 0;. Use for-each to read, the indexed loop to modify or when you need the position i.

Example

Two ways to sum an array:

Indexed: for (int i = 0; i < a.length; i++) { sum += a[i]; }
For-each: for (int x : a) { sum += x; }
Both give the same total; for-each is cleaner when the index isn't needed.

Key idea

A traversal visits every element. The indexed loop (for (int i = 0; i < a.length; i++)) gives the position i and can modify a[i]; the for-each loop (for (int x : a)) cleanly reads each value but can't change the array or use an index. Choose by whether you need the index or to modify.

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