Is a Quantity Prime in Java

The problem

Outline a perform that takes one integer argument and returns a logical worth true or false relying on if the integer is a chief.

Per Wikipedia, a chief quantity (or a chief) is a pure quantity higher than 1 that has no optimistic divisors aside from 1 and itself.

Necessities:

• You’ll be able to assume you’ll be given an integer enter.
• You cannot assume that the integer will probably be solely optimistic. Chances are you’ll be given adverse numbers as nicely (or “).
• NOTE on efficiency: There aren’t any fancy optimizations required, however nonetheless the most trivial options may day out. Numbers go as much as 2^31 (or comparable, is determined by language model). Looping all the best way as much as n, or n/2, will probably be too sluggish.

Instances:

is_prime(1)  /* false */
is_prime(2)  /* true  */
is_prime(-1) /* false */

The answer in Java code

Possibility 1:

public class Prime {
  public static boolean isPrime(int num) {
    return num > 1 && java.math.BigInteger.valueOf(num).isProbablePrime(20);
  }
}

Possibility 2:

public class Prime {
  public static boolean isPrime(int quantity) {
    if(quantity < 2)
      return false;
    for (int i=2; i<=Math.sqrt(quantity); i++){
      if(quantity % i == 0)
        return false;
    }
    return true;
  }
}

Possibility 3:

public class Prime {
  public static boolean isPrime(int num) {
    if (num == 2) return true;
    if (num < 2 || num % 2 == 0) return false;
    for (int i = 3; num >= i*i; i+=2) {
        if (num % i == 0) return false;
    }
    return true;
  }
}

Take a look at instances to validate our resolution

import static org.junit.Assert.assertTrue;
import static org.junit.Assert.assertFalse;
import org.junit.Take a look at;

public class PrimeTest {
	@Take a look at
	public void testBasic() {
		assertFalse("0  shouldn't be prime", Prime.isPrime(0));
		assertFalse("1  shouldn't be prime", Prime.isPrime(1));
		assertTrue ("2  is prime",     Prime.isPrime(2));
		assertTrue ("73 is prime",     Prime.isPrime(73));
		assertFalse("75 shouldn't be prime", Prime.isPrime(75));
		assertFalse("-1 shouldn't be prime", Prime.isPrime(-1));
	}
	@Take a look at
	public void testPrime() {
		assertTrue("3 is prime", Prime.isPrime(3));
		assertTrue("5 is prime", Prime.isPrime(5));
		assertTrue("7 is prime", Prime.isPrime(7));
		assertTrue("41 is prime", Prime.isPrime(41));
		assertTrue("5099 is prime", Prime.isPrime(5099));
	}
	@Take a look at
	public void testNotPrime() {
		assertFalse("4 shouldn't be prime", Prime.isPrime(4));
		assertFalse("6 shouldn't be prime", Prime.isPrime(6));
		assertFalse("8 shouldn't be prime", Prime.isPrime(8));
		assertFalse("9 shouldn't be prime", Prime.isPrime(9));
		assertFalse("45 shouldn't be prime", Prime.isPrime(45));
		assertFalse("-5 shouldn't be prime", Prime.isPrime(-5));
		assertFalse("-8 shouldn't be prime", Prime.isPrime(-8));
		assertFalse("-41 shouldn't be prime", Prime.isPrime(-41));
	}
}