Lesson 10 – Arrays

Arrays allow you to store multiple values in a single variable. They are used when you need a list of items such as numbers, names, or marks.

1. Creating an Array

public class Main {
    public static void main(String[] args) {
        int[] numbers = {10, 20, 30, 40};

        System.out.println(numbers[0]);  // 10
        System.out.println(numbers[2]);  // 30
    }
}

Arrays use index numbers starting from 0.

2. Changing Array Values

public class Main {
    public static void main(String[] args) {
        String[] names = {"Ali", "Sara", "Khalid"};

        names[1] = "Ayesha";

        System.out.println(names[1]);
    }
}

3. Array Length

public class Main {
    public static void main(String[] args) {
        int[] marks = {45, 70, 88, 92};

        System.out.println("Length: " + marks.length); 
    }
}

4. Looping Through an Array

Using a for loop

public class Main {
    public static void main(String[] args) {
        int[] nums = {3, 6, 9, 12};

        for (int i = 0; i < nums.length; i++) {
            System.out.println(nums[i]);
        }
    }
}

Using a for-each loop (easier)

public class Main {
    public static void main(String[] args) {
        String[] fruits = {"Apple", "Banana", "Mango"};

        for (String f : fruits) {
            System.out.println(f);
        }
    }
}

5. Finding the Largest Number in an Array

public class Main {
    public static void main(String[] args) {
        int[] numbers = {12, 55, 3, 90, 45};

        int max = numbers[0];

        for (int n : numbers) {
            if (n > max) {
                max = n;
            }
        }

        System.out.println("Largest: " + max);
    }
}

6. Calculating the Sum of an Array

public class Main {
    public static void main(String[] args) {
        int[] data = {5, 10, 15, 20};

        int total = 0;

        for (int d : data) {
            total += d;
        }

        System.out.println("Total = " + total);
    }
}

7. Arrays of Strings

public class Main {
    public static void main(String[] args) {
        String[] cities = {"Riyadh", "London", "Dubai", "Istanbul"};

        for (String c : cities) {
            System.out.println(c);
        }
    }
}

8. Passing an Array to a Method

public class Main {

    static void printArray(int[] arr) {
        for (int n : arr) {
            System.out.println(n);
        }
    }

    public static void main(String[] args) {
        int[] values = {2, 4, 6, 8};
        printArray(values);
    }
}

9. Returning an Array From a Method

public class Main {

    static int[] getMarks() {
        return new int[] {60, 75, 80, 95};
    }

    public static void main(String[] args) {
        int[] m = getMarks();

        for (int x : m) {
            System.out.println(x);
        }
    }
}

Summary

An array stores multiple values
Each value is accessed using an index starting from 0
You can loop through arrays using for or for-each
Arrays can be passed to methods
Methods can return arrays

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