Traversing Arrays

A traversal is the act of visiting every element of an array in some order. The most common pattern is left-to-right with an indexed for loop, but you'll also use enhanced for loops, reverse loops, and partial loops.

Choosing the right loop type matters. The indexed loop gives you the index (needed for modification or comparison with neighbors); the enhanced loop is cleaner when you only need values (and never modifies the array).

Traversals are the heart of nearly every array FRQ — sums, maxes, counts, filters, transformations. Build the patterns into muscle memory.

Standard for loop (with index)

int[] nums = {3, 1, 4, 1, 5, 9, 2};
for (int i = 0; i < nums.length; i++) {
    System.out.println(i + ": " + nums[i]);
}

Use this when you need the index — for example, to modify elements, compare with neighbors, or report positions.

Enhanced for loop (for-each)

for (int n : nums) {
    System.out.println(n);
}

Reads each element in order, one per iteration. The variable n is a copy of each element — assigning to it does not change the array.

Common traversal patterns

// Sum
int sum = 0;
for (int n : nums) sum += n;

// Maximum
int max = nums[0];
for (int i = 1; i < nums.length; i++) {
    if (nums[i] > max) max = nums[i];
}

// Count matches
int count = 0;
for (int n : nums) {
    if (n > 3) count++;
}

// Transform every element
for (int i = 0; i < nums.length; i++) {
    nums[i] = nums[i] * 2;
}

Partial traversals

// Skip the first element
for (int i = 1; i < nums.length; i++) { ... }

// Stop one before the end (e.g., compare with i+1)
for (int i = 0; i < nums.length - 1; i++) {
    if (nums[i] == nums[i + 1]) { ... }
}

Reverse traversal

for (int i = nums.length - 1; i >= 0; i--) {
    System.out.println(nums[i]);
}

Useful when shifting elements right or printing in reverse order.