The problem this code solves

A gradebook stores one score per student in an array. To show the class average, the top score, or how many passed, the program has to walk the whole array and do something with each score. That walk is a traversal, and nearly every array question on the exam is one. The only real choices are whether you need the index and whether you are reading or changing the data.

Traversing an array: visit every element, exactly once

An array stores its elements in numbered slots. The first is index 0 and the last is index length - 1. Almost every array algorithm is a traversal: walk the slots in order, doing something with each element.

Two ways to traverse

// index loop: you have the position i
for (int i = 0; i < data.length; i++) {
    System.out.println(data[i]);
}

// enhanced for-each: just the values
for (int x : data) {
    System.out.println(x);
}

data.length is the number of slots. Notice it is a field, so there are no parentheses (that is length, not length(), which is the String method).

The for-each catch: it is a copy

The bound: less-than, not less-than-or-equal

Vocabulary

Predict first, then check

See the traversal find the max

The maximum starts at index 0, then each element is compared to the best seen so far. Play it and watch the pointer walk the array while max updates.

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

Live code editor

Eight problems, six scaffolded and two open-ended. Write Java, press Run to execute it, and Check to test against the expected output. Hints and the solution are here if you need them, but using them is tracked, so try first.

Array Traversal Arcade

Six quick rounds. Read the array or the loop and type the result. Sharpens the index and for-each patterns you use on every array FRQ.

Multiple choice

Predict your answer before reading the options. Watch for the qualifier words. After you answer, the rationale explains every distractor.

FRQ connection: count within a range

FRQ 1 and the array FRQs lean on traversal plus a conditional. Practice it: walk the array and count the elements that fall in a range.

Choose your lane