Javan alkuluku: alkuluku on luku, joka on suurempi kuin 1 ja jaettuna 1:llä tai vain itsellään. Toisin sanoen alkulukuja ei voida jakaa muilla luvuilla kuin itsellään tai yhdellä. Esimerkiksi 2, 3, 5, 7, 11, 13, 17.... ovat alkulukuja.

Huomaa: 0 ja 1 eivät ole alkulukuja. 2 on ainoa parillinen alkuluku, koska kaikki muut parilliset luvut voidaan jakaa kahdella.

Katsotaanpa alkulukuohjelmaa javassa. Tässä java-ohjelmassa otamme lukumuuttujan ja tarkistamme, onko luku alkuluku vai ei.

 public class PrimeExample{ public static void main(String args[]){ int i,m=0,flag=0; int n=3;//it is the number to be checked m=n/2; if(n==0||n==1){ System.out.println(n+&apos; is not prime number&apos;); }else{ for(i=2;i<=m;i++){ if(n%i="=0){" system.out.println(n+' is not prime number'); flag="1;" break; } if(flag="=0)" { end of else < pre> <span> Test it Now </span> <p>Output:</p> <pre> 3 is prime number </pre> <h2>Prime Number Program using Method in Java</h2> <pre> public class PrimeExample2{ static void checkPrime(int n){ int i,m=0,flag=0; m=n/2; if(n==0||n==1){ System.out.println(n+&apos; is not prime number&apos;); }else{ for(i=2;i<=m;i++){ if(n%i="=0){" system.out.println(n+' is not prime number'); flag="1;" break; } if(flag="=0)" { end of else public static void main(string args[]){ checkprime(1); checkprime(3); checkprime(17); checkprime(20); < pre> <span> Test it Now </span> <p>Output:</p> <pre> 1 is not prime number 3 is prime number 17 is prime number 20 is not prime number </pre> <h2>Prime Number Program in Java (Another way)</h2> <p>You can also use a method where number is not predefined. Here, user has to put the number to check if the number is prime.</p> <pre> import java.util.Scanner; import java.util.Scanner; public class PrimeExample3 { public static void main(String[] args) { Scanner s = new Scanner(System.in); System.out.print(&apos;Enter a number : &apos;); int n = s.nextInt(); if (isPrime(n)) { System.out.println(n + &apos; is a prime number&apos;); } else { System.out.println(n + &apos; is not a prime number&apos;); } } public static boolean isPrime(int n) { if (n <= 1) { return false; } for (int i="2;" < math.sqrt(n); i++) if (n % 0) true; pre> <p>Output:</p> <strong>Use image PrimeExample1</strong> <h2>Find prime numbers between two numbers</h2> <p>You can also find prime numbers between two specified numbers.</p> <pre> import java.util.Scanner; public class PrimeExample4 { public static void main(String[] args) { Scanner s = new Scanner(System.in); System.out.print(&apos;Enter the first number : &apos;); int start = s.nextInt(); System.out.print(&apos;Enter the second number : &apos;); int end = s.nextInt(); System.out.println(&apos;List of prime numbers between &apos; + start + &apos; and &apos; + end); for (int i = start; i <= end; i++) { if (isprime(i)) system.out.println(i); } public static boolean isprime(int n) (n <="1)" return false; for (int i="2;" % 0) true; pre> <p>Output:</p> <strong>Use image PrimeExample2</strong> </=></pre></=></pre></=m;i++){></pre></=m;i++){>

Alkulukuohjelma Java-menetelmällä

 public class PrimeExample2{ static void checkPrime(int n){ int i,m=0,flag=0; m=n/2; if(n==0||n==1){ System.out.println(n+&apos; is not prime number&apos;); }else{ for(i=2;i<=m;i++){ if(n%i="=0){" system.out.println(n+\' is not prime number\'); flag="1;" break; } if(flag="=0)" { end of else public static void main(string args[]){ checkprime(1); checkprime(3); checkprime(17); checkprime(20); < pre> <span> Test it Now </span> <p>Output:</p> <pre> 1 is not prime number 3 is prime number 17 is prime number 20 is not prime number </pre> <h2>Prime Number Program in Java (Another way)</h2> <p>You can also use a method where number is not predefined. Here, user has to put the number to check if the number is prime.</p> <pre> import java.util.Scanner; import java.util.Scanner; public class PrimeExample3 { public static void main(String[] args) { Scanner s = new Scanner(System.in); System.out.print(&apos;Enter a number : &apos;); int n = s.nextInt(); if (isPrime(n)) { System.out.println(n + &apos; is a prime number&apos;); } else { System.out.println(n + &apos; is not a prime number&apos;); } } public static boolean isPrime(int n) { if (n <= 1) { return false; } for (int i="2;" < math.sqrt(n); i++) if (n % 0) true; pre> <p>Output:</p> <strong>Use image PrimeExample1</strong> <h2>Find prime numbers between two numbers</h2> <p>You can also find prime numbers between two specified numbers.</p> <pre> import java.util.Scanner; public class PrimeExample4 { public static void main(String[] args) { Scanner s = new Scanner(System.in); System.out.print(&apos;Enter the first number : &apos;); int start = s.nextInt(); System.out.print(&apos;Enter the second number : &apos;); int end = s.nextInt(); System.out.println(&apos;List of prime numbers between &apos; + start + &apos; and &apos; + end); for (int i = start; i <= end; i++) { if (isprime(i)) system.out.println(i); } public static boolean isprime(int n) (n <="1)" return false; for (int i="2;" % 0) true; pre> <p>Output:</p> <strong>Use image PrimeExample2</strong> </=></pre></=></pre></=m;i++){>

Alkulukuohjelma Javassa (toinen tapa)

Voit myös käyttää menetelmää, jossa numeroa ei ole ennalta määritetty. Täällä käyttäjän on asetettava numero tarkistaakseen, onko luku alkuluku.

 import java.util.Scanner; import java.util.Scanner; public class PrimeExample3 { public static void main(String[] args) { Scanner s = new Scanner(System.in); System.out.print(&apos;Enter a number : &apos;); int n = s.nextInt(); if (isPrime(n)) { System.out.println(n + &apos; is a prime number&apos;); } else { System.out.println(n + &apos; is not a prime number&apos;); } } public static boolean isPrime(int n) { if (n <= 1) { return false; } for (int i="2;" < math.sqrt(n); i++) if (n % 0) true; pre> <p>Output:</p> <strong>Use image PrimeExample1</strong> <h2>Find prime numbers between two numbers</h2> <p>You can also find prime numbers between two specified numbers.</p> <pre> import java.util.Scanner; public class PrimeExample4 { public static void main(String[] args) { Scanner s = new Scanner(System.in); System.out.print(&apos;Enter the first number : &apos;); int start = s.nextInt(); System.out.print(&apos;Enter the second number : &apos;); int end = s.nextInt(); System.out.println(&apos;List of prime numbers between &apos; + start + &apos; and &apos; + end); for (int i = start; i <= end; i++) { if (isprime(i)) system.out.println(i); } public static boolean isprime(int n) (n <="1)" return false; for (int i="2;" % 0) true; pre> <p>Output:</p> <strong>Use image PrimeExample2</strong> </=></pre></=>