Java Academy · Lesson

Array Basics & Iteration

Understand array basics: fixed-size, zero-based indexing, create/initialize, and iterate safely.

Lesson 1 of 38 steps

Array Basics & Iteration is a free Java Academy lesson on CoddyKit. This is lesson 1 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Java Academy learning path, and your progress syncs across the web and the CoddyKit app. The Java Academy course includes 3 lessons in total.

What is an array

Array is a fixed-size sequence of elements of the same type, stored under one name and indexed from 0.

Use when you know the element count
Access by index: first is 0
Type-safe: all items have the same type

Declare & Create

Declare and create arrays:

public class Main {
  public static void main(String[] args) {
    // Way 1: Declare an array with fixed size
    int[] a = new int[3];
    // All elements are 0 by default: [0, 0, 0]

    // Way 2: Declare and initialize in one line
    int[] b = {10, 20, 30};
    // This array already has values: [10, 20, 30]

    // Print both arrays
    System.out.print("Array a: ");
    for (int i = 0; i < a.length; i++) {
      System.out.print(a[i] + " ");
    }

    System.out.println(); // new line

    System.out.print("Array b: ");
    for (int i = 0; i < b.length; i++) {
      System.out.print(b[i] + " ");
    }
  }
}

Access & Update

Access and update by index:

Valid indices for 3 elements: 0, 1, 2.

public class Main {
  public static void main(String[] args) {
    // Create and initialize an array
    int[] a = {5, 7, 9}; // array has 3 elements: [5, 7, 9]

    // Access the first element (index 0)
    int first = a[0]; // first = 5
    System.out.println("First element: " + first);

    // Update the second element (index 1)
    a[1] = 8; // now array is [5, 8, 9]

    // Print the whole array to see the update
    System.out.print("Updated array: ");
    for (int i = 0; i < a.length; i++) {
      System.out.print(a[i] + " ");
    }
  }
}

Length & For

Use a.length to get the element count. Iterate with a for loop:

public class Main {
  public static void main(String[] args) {
    // Example array
    int[] a = {5, 8, 9}; // 3 elements

    int sum = 0; // start with 0

    // Loop through each element in the array
    for (int i = 0; i < a.length; i = i + 1) {
      // Add the current element to sum
      sum = sum + a[i];
    }

    // Print the final result
    System.out.println("Sum of array elements = " + sum);
  }
}

For-each

Enhanced for-each reads elements without index:

int total = 0;
for (int v : b) {
  total = total + v;
}

Use when you do not need the index.

Array Demo

Run it: The demo prints the length, sum, max, and every element using for and for-each.

public class Main {
  static int sum(int[] arr) {
    int s = 0;
    for (int i = 0; i < arr.length; i = i + 1) {
      s = s + arr[i];
    }
    return s;
  }

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

  public static void main(String[] args) {
    int[] nums = {3, 1, 4, 1, 5};

    System.out.println("Length = " + nums.length);
    System.out.println("Sum = " + sum(nums));
    System.out.println("Max = " + max(nums));

    System.out.println("Elements:");
    for (int v : nums) {
      System.out.println(v);
    }
  }
}

Array Length

Quick check: How do you get the number of elements in array a?

Answer it in the interactive lesson

Recap & Next

Recap: You created arrays, accessed and updated items, used length, and iterated with for and for-each.

Next: Learn common array algorithms like search and reverse.

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Frequently Asked Questions

Is the “Array Basics & Iteration” lesson free?

Yes — the full text of “Array Basics & Iteration” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Java Academy course, upgrade to CoddyKit PRO. The Java Academy course includes 3 lessons in total.

What will I learn in “Array Basics & Iteration”?

Understand array basics: fixed-size, zero-based indexing, create/initialize, and iterate safely. You practise Java Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Java Academy?

No prior experience is required. Java Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 3.

How long does the “Array Basics & Iteration” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Java Academy lesson?

Yes. Every Java Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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