Java Basic Examples

Check if a number is prime number in Java Example

This Example shows how to check if a number is prime number in Java. This example also shows how to find prime numbers between 1 and 100 or any two numbers.

What is a prime number?

Definition of a prime number from Wikipedia,

A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself.

How to check if a number is prime number in Java?

If we cannot divide a number (greater than 1) by any positive number other than 1 or itself, then the number is a prime number. We will use modulus operator (%) to check if we can divide the number as given below.

Output

As you may have observed from the above code, for loop inside the isPrimeNumber goes only up to number/2. That is because any number cannot be perfectly divided by anything above the half of that number.

How to find prime number between 1 and 100?

We will do a slight modification to the above program to find prime numbers between 1 and 100 as given below.

Output

Here, we have introduced a new loop which goes through 2 to 100 and checks the number one by one. Inner loop goes from 2 to the half of the number and tries to divide. If reminder of the any of the division is zero than the number is not a prime number.

How to find prime numbers between 1 to n?

In above example, we printed prime numbers between 1 and 100. Now, we are going to take input from user using Scanner and print the prime numbers between 2 and input number as given below.

Output

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