In this article, you'll learn to check whether a number is prime or not. This is done using a for loop and while loop in Java.

A prime number is a number which is divisible by only two numbers: 1 and itself. So, if any number is divisible by any other number, it is not a prime number.

```
public class Prime {
public static void main(String[] args) {
int num = 29;
boolean flag = false;
for(int i = 2; i <= num/2; ++i)
{
// condition for nonprime number
if(num % i == 0)
{
flag = true;
break;
}
}
if (!flag)
System.out.println(num + " is a prime number.");
else
System.out.println(num + " is not a prime number.");
}
}
```

When you run the program, the output will be:

29 is a prime number.

In the above program, for loop is used to determine if the given number `num` is prime or not. We only have to loop through 2 to half of `num`, because no number is divisible by more than its half.

Inside the for loop, we check if the number is divisible by any number in the given range `(2..num/2)`

. If it is, `flag` is set to `true`

and we break out of the loop. This determines `num` is not a prime number.

If `num` isn't divisible by any number, `flag` is false and `num` is a prime number.

```
public class Prime {
public static void main(String[] args) {
int num = 33, i = 2;
boolean flag = false;
while(i <= num/2)
{
// condition for nonprime number
if(num % i == 0)
{
flag = true;
break;
}
++i;
}
if (!flag)
System.out.println(num + " is a prime number.");
else
System.out.println(num + " is not a prime number.");
}
}
```

When you run the program, the output will be:

33 is not a prime number.

In the above program, while loop is used instead of a for loop. The loop runs until `i <= num/2`

. On each iteration, whether `num` is divisble by `i` is checked and the value of `i` is incremented by 1.

Visit this page to learn, how you can display all prime numbers between two intervals.