Arrays in Java

An array stores a fixed-size collection of elements of the same type. Arrays make it possible to process many values with a single variable name. They are zero-indexed and offer constant-time access by index.

• Declare: int arr[]; or int[] arr;
• Create: arr = new int[5];
• Initialize: int arr[] = {10, 20, 30};
• Access: arr[0], length via arr.length.

Let's start with a hands-on example. The program below shows the core idea behind Arrays in just a few lines of Java. Read it line by line and observe how Java executes each statement in order.

class Main
{
    public static void main(String args[])
    {
        int arr[] = {10, 20, 30, 40, 50};

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

The following examples progress from simple to more practical patterns. Try each in your IDE, change the inputs and observe the output. This is the fastest way to internalize the concept.

class Main
{
    public static void main(String args[])
    {
        int arr[] = {5, 10, 15, 20};
        int sum = 0;

        for (int x : arr)
            sum += x;

        System.out.println("Sum = " + sum);
    }
}

class Main
{
    public static void main(String args[])
    {
        int arr[] = {12, 78, 23, 45, 67};
        int max = arr[0];

        for (int x : arr)
            if (x > max) max = x;

        System.out.println("Max = " + max);
    }
}

import java.util.Arrays;

class Main
{
    public static void main(String args[])
    {
        int arr[] = {5, 1, 4, 2, 3};

        Arrays.sort(arr);

        System.out.println(Arrays.toString(arr));
    }
}

class Main
{
    public static void main(String args[])
    {
        int arr[] = {1, 2, 3, 4, 5};

        for (int i = arr.length - 1; i >= 0; i--)
            System.out.print(arr[i] + " ");
    }
}

class Main
{
    public static void main(String args[])
    {
        int arr[] = {10, 25, 40, 55};
        int key = 40, idx = -1;

        for (int i = 0; i < arr.length; i++)
            if (arr[i] == key) { idx = i; break; }

        System.out.println("Index = " + idx);
    }
}

• Arrays in Java are objects, not primitive types.
• Default values are 0 / 0.0 / null / false based on type.
• Accessing an invalid index throws ArrayIndexOutOfBoundsException.
• Use Arrays.toString(arr) for pretty-printing.
• Arrays have fixed length — for resizable storage use ArrayList.

Reading is not enough — practice solidifies knowledge. Try every question below in your own editor before peeking at any solution.

• Q1. Find the minimum element of an array.
• Q2. Count even and odd numbers in an array.
• Q3. Find the second largest number in an array.
• Q4. Check if an array contains a target value.
• Q5. Compute the average of all array elements.

These are the most common questions asked in Java interviews on this topic. Memorize the concept, not just the answer — interviewers often follow up with edge cases.

Even experienced developers slip on the same pitfalls. Watch out for these classic mistakes while working with Arrays in Java:

• Forgetting the semicolon ; at the end of statements while using Arrays.
• Mixing up similar method names — read Java docs before using new APIs related to Arrays.
• Ignoring compiler warnings — they often hint at bugs that will appear later in production.
• Hard-coding values that should come from configuration files or environment variables.
• Not handling edge cases: empty inputs, very large inputs, negative numbers and null references.
• Skipping unit tests — small tests prevent big regressions, especially around control flow.