To check if a number is prime in Java, check whether this number divides by any number before it, using the

`for`

loop.Here's how you do it:

```
public class IsPrime {
public static void main(String[] args) {
System.out.println(isPrime(1)); // false
System.out.println(isPrime(4)); // false
System.out.println(isPrime(31)); // true
System.out.println(isPrime(53)); // true
System.out.println(isPrime(52)); // false
}
static boolean isPrime(int n) {
if (n <= 1) return false;
for (int i = 2; i < n; i++) if (n % i == 0) return false;
return true;
}
}
```