Java Programming Examples Tutorial Index

Java Number Programs

This Java program demonstrates how to calculate and print prime numbers. Whether you aim to print prime numbers from 1 to 100 in Java or want to understand the logic behind identifying a prime number in Java, this tutorial has you covered.

What is a Prime Number?

Prime numbers are unique natural numbers greater than 1, divisible only by 1 and themselves. Unlike composite numbers, they can't be divided by smaller natural numbers. Prime numbers are significant in fields like number theory, cryptography, and computer science.

Examples of prime numbers:

A few prime numbers are 2, 3, 5, 7, 11, and 13. These numbers can only be divided evenly by 1 or themselves, so they are prime numbers.

Prime Number Check Program in Java


public class PrimeNumbers {
  public static void main(String[] args) {
    int num = 20;  // Define the upper limit
    int count;  // Initialize counter for divisibility checks

    // Iterate from 1 up to 'num' to identify prime numbers
    for (int i = 1; i <= num; i++) {
      count = 0;  // Reset counter for each 'i'

      // Check for divisibility from 2 up to i/2
      for (int j = 2; j <= i / 2; j++) {
        if (i % j == 0) {
          count++;  // Increment if 'i' is divisible by 'j'
          break;  // Exit loop if a divisor is found

      // If the count is 0, 'i' is prime
      if (count == 0) {
        System.out.println(i);  // Output the prime number

Program Output:

Execute this Java program to generate prime numbers. You will get the list of prime numbers up to 20 as follows:


Code Explanation:

Here is a line-by-line explanation of the prime no program in Java:

  1. Class and Main Method: First, create a class named PrimeNumbers. Inside this class, declare the main() method.
  2. Variable Initialization: Declare two integer variables num and count. Set num to 20, which is the upper limit for the prime number search.
  3. Outer Loop: An outer loop runs from 1 to num. Initialize count to zero at the start of each iteration.
  4. Inner Loop: An inner loop runs from 2 to i / 2 and checks if i is divisible by any number in this range. If a divisor is found, count increments by one, and the loop exits.
  5. Prime Identification: After the inner loop, if count remains zero, the program considers i as a prime number and prints it.


This Java tutorial provides an efficient and straightforward way to calculate prime numbers up to a given limit. Whether you aim to print a list of prime numbers in Java or understand the core logic behind identifying them, this guide makes it accessible to everyone.

Found This Page Useful? Share It!
Get the Latest Tutorials and Updates
Join us on Telegram