## Wednesday, June 22, 2022

### Java Program to Check Whether Number Prime or Not

This post shows a Java program to check whether the passed number is a prime number or not.

A number is a prime number if can be divided either by 1 or by the number itself. So the logic for your program should be to run a for loop and divide the passed number every time in that loop, if it completely divides any time then the passed number is not a prime number. You only need to run your loop from 2 till N/2 (where N is the passed number), reason being no number is completely divisible by a number more than its half.

### Java program to check whether the number is prime or not

```import java.util.Scanner;

public static void main(String[] args) {
// Using Scanner class to take input
Scanner sc = new Scanner(System.in);
System.out.println("Enter number - ");
int num = sc.nextInt();
boolean flag = isNumberPrime(num);
if(flag){
System.out.println(num + " is a prime number");
}else{
System.out.println(num + " is not a prime number");
}
}

private static boolean isNumberPrime(int num){
boolean flag = true;
for(int i = 2; i <= num/2; i++){
// No remainder means completely divides
if(num % i == 0){
flag = false;
break;
}
}
return flag;
}
}
```
Output
```Enter number -
7
7 is a prime number

Enter number -
10
10 is not a prime number
```

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