Java Academy · Lesson

Array Basics & Iteration

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

Array Basics & Iteration is a free Java Academy lesson on CoddyKit — 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, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.

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?

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.

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, and the Java Academy course includes 3 lessons in total. 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.

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; this is — lesson 1 of 3, so you can start here or from the beginning and move at your own pace.

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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