Java Programs for Practice: Prime, Factorial, Patterns and More

A hello program in Java is a three-line class that prints text to the screen using System.out.println. Create a file named HelloWorld.java, declare a public class, add a main method, and write your print statement inside it. Compile with javac HelloWorld.java and run with java HelloWorld. That is the complete hello program in Java every beginner must master first.

• Key Takeaway 1: The hello program in Java is the entry point for every beginner. Get it right and the rest follows naturally.
• Key Takeaway 2: Prime number and factorial programs teach you loops and conditionals, the two building blocks of almost every algorithm.
• Key Takeaway 3: Pattern printing forces you to think in nested loops, a skill that directly prepares you for 2D array problems in coding interviews.
• Key Takeaway 4: Switch-case programs give you a clean alternative to long if-else chains and are tested frequently in campus placements.
• Key Takeaway 5: Practising these core Java programs consistently is one of the top skills every college student must build before graduation.

Hello World and Basic Java Programs Every Beginner Needs

Before you write a single algorithm, you need to understand how a Java program is structured. Every Java file needs a public class whose name matches the filename, a public static void main(String[] args) method, and at least one statement inside it. That is the skeleton. Everything else is logic you add on top.

Hello Program in Java: Hello World

The hello program in Java below is the standard starting point taught in every computer science department, from IITs to tier-3 colleges. Save the file as HelloWorld.java, compile with javac HelloWorld.java, and run with java HelloWorld.

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Output: Hello, World!

System.out.println sends text to the standard output stream and adds a newline at the end. It is the most-used output method in beginner Java programs. Every time you write a hello program in Java, this is the line doing the actual work.

Sum of Two Numbers in Java

public class SumTwo {
    public static void main(String[] args) {
        int a = 15, b = 27;
        int sum = a + b;
        System.out.println("Sum: " + sum);
    }
}

Output: Sum: 42

This program introduces variable declaration, assignment and arithmetic, three concepts you will use in every program you ever write.

Sum of Digits of a Number in Java

public class SumOfDigits {
    public static void main(String[] args) {
        int num = 1234, sum = 0;
        while (num != 0) {
            sum += num % 10;
            num /= 10;
        }
        System.out.println("Sum of digits: " + sum);
    }
}

Output: Sum of digits: 10

The modulus operator strips the last digit each iteration, and integer division shrinks the number. The loop stops when nothing is left. This is one of the most commonly asked questions in Java written tests at Indian IT companies including TCS, Infosys and Wipro.

Switch Case in Java

public class DayName {
    public static void main(String[] args) {
        int day = 3;
        switch (day) {
            case 1: System.out.println("Monday"); break;
            case 2: System.out.println("Tuesday"); break;
            case 3: System.out.println("Wednesday"); break;
            default: System.out.println("Other day");
        }
    }
}

Output: Wednesday

Switch-case examples like this appear in placement tests for Infosys, TCS and Wipro. The break keyword prevents fall-through, which is a classic bug source for beginners who forget it.

Prime Number and Factorial Programs in Java

These two programs come up in nearly every Java interview and campus placement test in India. According to NASSCOM’s 2023 Talent Report, over 60% of entry-level IT hiring in India involves a coding round that includes basic number programs. Getting these right matters.

Prime Number Program in Java

A prime number is divisible only by 1 and itself. The most efficient beginner approach checks divisibility only up to the square root of the number, cutting unnecessary iterations.

public class PrimeCheck {
    public static void main(String[] args) {
        int num = 29;
        boolean isPrime = true;
        if (num < 2) isPrime = false;
        for (int i = 2; i <= Math.sqrt(num); i++) {
            if (num % i == 0) { isPrime = false; break; }
        }
        System.out.println(num + (isPrime ? " is prime" : " is not prime"));
    }
}

Output: 29 is prime

The Math.sqrt() trick reduces the number of checks from O(n) to O(n). For the number 29, that means checking only up to 5 instead of 28. This prime number program in Java is the version interviewers expect you to know, not the naive loop-to-n version.

Factorial Program in Java

Factorial of n (written n!) is the product of all positive integers up to n. Factorial of 5 is 5 x 4 x 3 x 2 x 1 = 120.

public class Factorial {
    public static void main(String[] args) {
        int num = 5;
        long factorial = 1;
        for (int i = 1; i <= num; i++) {
            factorial *= i;
        }
        System.out.println("Factorial of " + num + " = " + factorial);
    }
}

Output: Factorial of 5 = 120

Using long instead of int is deliberate. Factorial grows fast. Factorial of 13 already exceeds the int range of 2,147,483,647. Always use long unless you are certain the input stays small.

Fibonacci Series in Java

public class Fibonacci {
    public static void main(String[] args) {
        int n = 8, a = 0, b = 1;
        System.out.print("Fibonacci: " + a + " " + b);
        for (int i = 2; i < n; i++) {
            int c = a + b; a = b; b = c;
            System.out.print(" " + c);
        }
    }
}

Output: Fibonacci: 0 1 1 2 3 5 8 13

Each term is the sum of the two before it. This program also comes up in dynamic programming discussions at senior levels, so learning the iterative version first gives you a strong base.

Pattern Printing in Java

Patterns in Java are built using nested loops. The outer loop controls rows, the inner loop controls columns. Once you understand that relationship, every pattern from triangles to diamonds becomes a variation of the same idea.

Right-Angled Triangle Pattern

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

Output:

*
* *
* * *
* * * *
* * * * *

Number Pattern

public class NumberPattern {
    public static void main(String[] args) {
        int rows = 4;
        for (int i = 1; i <= rows; i++) {
            for (int j = 1; j <= i; j++) {
                System.out.print(j + " ");
            }
            System.out.println();
        }
    }
}

Output:

1
1 2
1 2 3
1 2 3 4

Pattern programs are a staple of Java practice in Indian engineering colleges. According to a GeeksforGeeks 2024 interview preparation survey, pattern printing questions appear in over 45% of freshers' coding assessments at mid-tier Indian IT firms. Practising 10 to 15 pattern variations is enough to handle most of what you will see in TCS NQT, AMCAT and CoCubes assessments.

Comparison of Core Java Practice Programs

How to Build on These Programs and What to Learn Next

Mastering these programs is not the finish line. It is the starting gate. Once you are comfortable with loops, conditionals and basic I/O in Java, you are ready to move into object-oriented programming, collections, exception handling and eventually data structures and algorithms.

According to the 2023 Stack Overflow Developer Survey, Java remains one of the top five most-used programming languages globally, with strong adoption across enterprise software, Android development and backend systems. In India specifically, Java is the primary language tested in campus placements at companies like Accenture, Cognizant, HCL and Tech Mahindra.

If you are a student or fresh graduate wondering which direction to take your skills next, check out entry-level job options for teens and graduates to see where Java skills actually open doors. And if you are thinking about longer-term career direction, the guide on how to choose the right career path after graduation in 2026 is worth reading before you commit to a specialisation.

For working professionals looking to upskill, Java is often paired with cloud computing, cybersecurity or AI to build higher-value profiles. You can explore top online courses for high-salary jobs to see which combinations are paying off in the current market. If budget is a concern, the list of best free online learning platforms for students in 2025 has solid Java resources at no cost.

Career switchers benefit from understanding the full picture before they invest time. The breakdown of best career options in 2026 for students and professionals shows where Java fits in the broader tech hiring picture. You can also browse 3.0 University's full course catalogue if you want structured, certification-backed learning in cybersecurity, ethical hacking, AI, blockchain or Web3.

Your practical next steps this week: install JDK 17 from Oracle's official site, set up VS Code with the Java Extension Pack, and run every program on this page from scratch without copying. Type it out. That muscle memory matters more than you think. Then write three variations of each program, change the input values, break the code intentionally and fix it. That process builds real understanding, not just familiarity.

3.0 University offers industry-aligned certification programmes that take you from these foundational programs into specialisations that employers are actively hiring for right now. Whether you are aiming for a cybersecurity role, an AI engineering track or a Web3 development path, the courses are built around practical, hands-on skills you can demonstrate in interviews and on the job.

Frequently Asked Questions

How do you write a hello program in Java?

Create a file named HelloWorld.java, declare a public class with the same name, add a public static void main(String[] args) method, and write System.out.println("Hello, World!"); inside it. Compile with javac HelloWorld.java and run with java HelloWorld. The hello program in Java is the first thing every beginner should get running before moving to anything else. See 3.0 University's course catalogue for structured Java learning paths.

What does System.out.println do in Java?

System.out.println prints the specified text to the standard output stream and moves the cursor to a new line. It is the most common output method in beginner Java programs. System.out.print does the same without the newline. Every hello program in Java uses System.out.println as its core output statement.

How do you compile and run a Java program from the command line?

Save your file with a .java extension matching the class name exactly. Open a terminal, navigate to the file location, and run javac FileName.java to compile. If there are no errors, run java FileName to execute. You need JDK 8 or higher installed. This two-step process applies to every Java program including the basic hello program in Java.

How do you check for a prime number in Java?

A prime number program in Java uses a loop from 2 to Math.sqrt(num) and checks if any number divides evenly into the target using the modulus operator. If any divisor is found, the number is not prime. Using Math.sqrt makes the check significantly faster than looping all the way to the number itself, which matters when inputs get large.

How do you write a factorial program in Java?

A factorial program in Java uses a for loop that multiplies a running total by each integer from 1 to n. Declare the result variable as long to avoid overflow for inputs above 12. Factorial of 5 returns 120, factorial of 10 returns 3,628,800. This is one of the most tested programs in Indian campus placement coding rounds including TCS NQT and Infosys InfyTQ.

How do you print patterns in Java?

Patterns in Java use nested for loops. The outer loop runs once per row, the inner loop runs once per column position in that row. Changing the inner loop's start and end condition changes the shape. A right-angled star triangle runs the inner loop from 1 to the current row number. Practising 10 to 15 pattern types covers most interview scenarios in AMCAT and CoCubes assessments.

How do you find the sum of digits in Java?

Use a while loop that runs as long as the number is not zero. Inside the loop, add num % 10 to a sum variable to extract the last digit, then divide num by 10 to remove it. Repeat until all digits are processed. For the number 1234, the sum of digits in Java is 1+2+3+4 = 10. This logic appears in many number manipulation questions across Indian IT placement tests.

Last updated: September 2026. Reviewed by the 3University editorial team.