Java Program to Check Prime Number

Posted in Java Tutorial

Updated on Oct 30, 2024

By Mari Selvan

👁️ 131 - Views

⏳ 4 mins

💬 1 Comment

Photo Credit to CodeToFun

🙋 Introduction

In the landscape of programming, dealing with prime numbers is a fundamental and interesting task. Prime numbers, those divisible only by 1 and themselves, play a crucial role in various mathematical and computational applications.

In this tutorial, we'll explore a Java program that efficiently checks whether a given number is a prime number.

📄 Example

Let's examine the Java code that performs the prime number check.

PrimeChecker.java

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public class PrimeChecker {

// Function to check if a number is prime
static boolean isPrime(int number) {
  // 0 and 1 are not prime numbers
  if (number <= 1) {
    return false;
  }

  // Check for factors from 2 to the square root of the number
  for (int i = 2; i * i <= number; ++i) {
    if (number % i == 0) {
      return false; // Found a factor, not a prime number
    }
  }

  return true; // No factors found, it's a prime number
}

// Driver program
public static void main(String[] args) {
  // Replace this value with your desired number
  int testNumber = 17;

  // Call the function to check if the number is prime
  if (isPrime(testNumber)) {
    System.out.println(testNumber + " is a prime number.");
  } else {
    System.out.println(testNumber + " is not a prime number.");
  }
}
}

💻 Testing the Program

To test the program with a different number, replace the value of testNumber in the main method.

Output

17 is a prime number.

Compile and run the program to see whether the number is a prime number.

🧠 How the Program Works

The program defines a class PrimeChecker containing a static method isPrime that takes an integer as input and returns a boolean indicating whether the number is prime.
Inside the method, it checks if the number is less than or equal to 1; if so, it's not prime.
It then iterates through potential factors from 2 to the square root of the number.
If it finds any factor, the number is not prime; otherwise, it is prime.
The main method tests the program with a specific number (in this case, 17).

📏 Between the Given Range

Let's dive into the java code that checks and lists prime numbers in the specified range.

PrimeNumberChecker.java

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public class PrimeNumberChecker {

// Function to check if a number is prime
static boolean isPrime(int number) {
  if (number <= 1) {
    return false;
  }
  for (int i = 2; i <= Math.sqrt(number); i++) {
    if (number % i == 0) {
      return false;
    }
  }
  return true;
}

// Driver program
public static void main(String[] args) {
  System.out.print("Prime Numbers in the Range 1 to 20: ");

  // Check prime numbers in the range 1 to 20
  for (int i = 1; i <= 20; i++) {
    if (isPrime(i)) {
      System.out.print(i + " ");
    }
  }

  System.out.println();
}
}

💻 Testing the Program

The program is set to check and list prime numbers in the range from 1 to 20. No additional input is required.

Output

Prime Numbers in the Range 1 to 20:
2 3 5 7 11 13 17 19

Compile and run the program to see the prime numbers in the specified range.

🧠 How the Program Works

The program defines a class PrimeNumberChecker containing a static method isPrime that checks if a number is prime.
Inside the isPrime method, it iterates from 2 to the square root of the number to check for factors.
The main method tests the prime numbers in the range from 1 to 20 and prints the result.

🧐 Understanding the Concept of Prime Numbers

Before diving into the code, let's briefly understand prime numbers.

A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers. For example, 2, 3, 5, 7, 11, and 13 are prime numbers.

🎢 Optimizing the Program

While the provided program is effective, you can explore optimizations such as using the square root of the number as the loop limit for improved efficiency.

Feel free to incorporate and modify this code as needed for your specific use case. Happy coding!