Have you ever sat, staring at your computer, with your coffee in your hand, thinking- how am I supposed to write a prime number program in Java and not screw it up!<\/p>\n
Well, I\u2019ve been there. A long time before I learned how to write code, I was haunted by the sight of prime numbers in Java<\/a> program assignments.<\/span> Sounds simple on paper, right? A whole that can be divided into only 1.<\/span> However, once you begin writing the logic, then you suddenly fall into the trap of an infinite loop (pun intended \ud83d\ude09).<\/span><\/p>\n This is why today I am going to take you through prime numbers in Java program the most human way.<\/span> No jargon overload. Clear examples, stories, and precise mistakes I made (so you do not need to repeat them).<\/span><\/p>\n In general, a prime number is just a number that is greater than 1, and cannot be divided into two parts, other than the parts of 1 and the parts of itself.<\/p>\n Examples:<\/p>\n 2, 3, 5, 7, 11, 13 \u2705 (prime)<\/p>\n 4, 6, 8, 9, 10 \u274c (not prime)<\/p>\n The only even prime number is 2.<\/span> This small fact served me wrong in my Java program.<\/span> I\u2019ll explain later.<\/p>\n In case you think, Why should I even bother with prime numbers in Java program, here it is:<\/p>\n And thus, not to pass exams, it is about the development of your coding muscles \ud83d\udcaa.<\/p>\n The following is the simplest I wrote as a beginner.<\/span> Well, it is not the most efficient, but it works.<\/span><\/p>\n This is what is referred to as the brute force method.<\/span> It verifies divisibility of all the numbers between 2 and n-1.<\/span> Inefficient, educational.<\/span><\/p>\n Then I thought… it isn’t necessary to check all numbers up to n-1, to check up to n.<\/span> That reduced my code run time by a lot.<\/span><\/p>\n This version made me realize the difference between smart code and code that writes more lines but not the right lines.<\/p>\n Recursion was popular with some of my friends.<\/span> It terrified me personally.<\/span> However, after I wrote the program to compute prime numbers in Java with recursion, I found it so beautiful:<\/span><\/p>\n That is fine to check a single number, but what about a list of primes in the range [1, 100]?<\/span> That\u2019s when loops save the day:<\/p>\n And you are committing these errors now, it is all right.<\/span> All coders do at some time.<\/span><\/p>\n The Java program on writing a prime numbers program taught me not only how to write a Java program, but also patience, optimization, and problem solving.<\/span> I initially stumbled along with basic loops, then got to know recursion, and eventually understood advanced algorithms such as the Sieve of Eratosthenes.<\/span><\/p>\n This is one of the best places to begin when you are learning Java.<\/span> It\u2019s small, yet powerful. And remember: you write a prime number program with Java, not once only not twice, but a hundred and a thousand times, you are not writing code, but a set of habits you will carry you through the next hundred and a thousand lines of code.<\/span><\/p>\n \ud83d\udc4d In case you want to learn more about Java, you can visit our Java Course<\/a> or Java Full Stack Development Course<\/a> and Internship, visit our website www.kaashivinfotech.com.<\/a><\/span><\/p>\nWhat are Prime Numbers (Quick Refresher \ud83e\uddee)<\/h2>\n
Why Prime Numbers in Java Program<\/h2>\n
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Prime Numbers in Java Program: The Basic Approach<\/h2>\n
public class PrimeCheck {\r\n public static void main(String[] args) {\r\n int num = 29; \/\/ you can try with any number\r\n boolean isPrime = true;\r\n\r\n if (num <= 1) {\r\n isPrime = false;\r\n } else {\r\n for (int i = 2; i < num; i++) {\r\n if (num % i == 0) {\r\n isPrime = false;\r\n break;\r\n }\r\n }\r\n }\r\n\r\n if (isPrime)\r\n System.out.println(num + \" is a prime number.\");\r\n else\r\n System.out.println(num + \" is not a prime number.\");\r\n }\r\n}\r\n<\/pre>\nOptimized Prime Numbers in Java Program (Method 2)<\/h2>\n
public class PrimeCheckOptimized {\r\n public static void main(String[] args) {\r\n int num = 29;\r\n boolean isPrime = true;\r\n\r\n if (num <= 1) {\r\n isPrime = false;\r\n } else {\r\n for (int i = 2; i <= Math.sqrt(num); i++) {\r\n if (num % i == 0) {\r\n isPrime = false;\r\n break;\r\n }\r\n }\r\n }\r\n\r\n if (isPrime)\r\n System.out.println(num + \" is a prime number.\");\r\n else\r\n System.out.println(num + \" is not a prime number.\");\r\n }\r\n}\r\n<\/pre>\nPrime Numbers in Java Program Using Recursion (Method 3)<\/h2>\n
public class PrimeRecursion {\r\n static boolean isPrime(int num, int i) {\r\n if (num <= 2)\r\n return (num == 2) ? true : false;\r\n if (num % i == 0)\r\n return false;\r\n if (i * i > num)\r\n return true;\r\n return isPrime(num, i + 1);\r\n }\r\n\r\n public static void main(String[] args) {\r\n int num = 29;\r\n if (isPrime(num, 2))\r\n System.out.println(num + \" is a prime number.\");\r\n else\r\n System.out.println(num + \" is not a prime number.\");\r\n }\r\n}\r\n<\/pre>\nGenerate Prime Numbers in Java Program (Method 4)<\/h2>\n
public class PrimeList {\r\n public static void main(String[] args) {\r\n int limit = 100;\r\n\r\n for (int num = 2; num <= limit; num++) {\r\n boolean isPrime = true;\r\n\r\n for (int i = 2; i <= Math.sqrt(num); i++) {\r\n if (num % i == 0) {\r\n isPrime = false;\r\n break;\r\n }\r\n }\r\n\r\n if (isPrime)\r\n System.out.print(num + \" \");\r\n }\r\n }\r\n}\r\n<\/pre>\nTypical errors that I committed when writing the Prime Number in Java Program.<\/h2>\n
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Final Thoughts \u2764\ufe0f<\/h2>\n
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