Today, I will show you how to create prime number program with Java.

**What is prime number?**

A prime number is a whole number greater than 1, whose only two whole-numberfactors are 1 and itself. The first few prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23, and 29.

**How to check if given number X is prime or not?**

This method will return true if X is prime and return false if X is not prime.

Time complexity for this algorithm are O( sqrt(X) ).

Time complexity for this algorithm are O( sqrt(X) ).

1 2 3 4 5 6 7 8 9 10 | public boolean isPrime(int x) { if(x<2) return false; if(x==2 || x==3) return true; if(x%2==0 || x%3==0) return false; for(int p=6; (p-1) * (p-1) <= x; p += 6) { if(x % (p-1) == 0 ) return false; if(x % (p+1) == 0 ) return false; } return true; } |

**How to generate prime number between A and B inclusive?**

A must be less than or equal B.

Time complexity for this algorithm are O( range * sqrt(range) ), where range = B - A

1 2 3 4 5 6 7 8 9 | public List<Integer> genPrimes(int a, int b) { List<Integer> primes = new ArrayList<Integer>(); if(a<= 2) primes.add(2); if(a % 2 == 0) a++; for(int p=a; p<=b; p+=2) { if(isPrime(p)) primes.add(p); } return primes; } |

If you want faster algorithm, please check my other post:

- Generate Prime Number With Dynamic Programming
- Prime Number With Sieve Algorithm (C++)
- Sieve With Optimized Memory (Java)

**Feel free to add your question or comment.**

**For urgent request please send email to**

**algojava8@gmail.com**

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