For Loop in Java

The for loop is the most popular loop in Java. It combines initialization, condition and update into a single line, making code compact and readable. Use it whenever the number of iterations is known in advance.

• Syntax: for (init; condition; update) { body }
• init runs once at the start.
• condition checked before each iteration.
• update runs after each iteration.

Let's start with a hands-on example. The program below shows the core idea behind For Loop 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[])
    {
        for (int i = 1; i <= 10; i++)
        {
            System.out.println(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 sum = 0;

        for (int i = 2; i <= 20; i += 2)
            sum += i;

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

class Main
{
    public static void main(String args[])
    {
        int n = 7;

        for (int i = 1; i <= 10; i++)
            System.out.println(n + " x " + i + " = " + (n * i));
    }
}

class Main
{
    public static void main(String args[])
    {
        for (int i = 5; i >= 1; i--)
            System.out.println(i);
    }
}

class Main
{
    public static void main(String args[])
    {
        for (int i = 1; i <= 5; i++)
        {
            for (int j = 1; j <= i; j++)
                System.out.print("* ");
            System.out.println();
        }
    }
}

class Main
{
    public static void main(String args[])
    {
        int arr[] = {12, 25, 7, 38, 19};

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

• All three parts of the for loop are optional — for(;;) is a valid infinite loop.
• Declare the loop variable inside the for() to limit its scope.
• Use long instead of int if your counter may exceed 2.1 billion.
• Avoid modifying the loop variable inside the body — it harms readability.
• Use the for-each loop whenever the index is not needed.

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

• Q1. Print all multiples of 5 between 1 and 100.
• Q2. Compute the factorial of 7 using a for loop.
• Q3. Print a pyramid star pattern of height 6.
• Q4. Find sum of digits of a number using a for loop.
• Q5. Print all prime numbers between 1 and 50.

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 For Loop in Java:

• Forgetting the semicolon ; at the end of statements while using For Loop.
• Mixing up similar method names — read Java docs before using new APIs related to For Loop.
• 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.