The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143 ?

LargestPrimeFactor.java

public class LargestPrimeFactor {
	private long num;
	public LargestPrimeFactor(long num){
		this.num=num;
	}
	public long calculate(){
		for(long i=1;i<=num/2;i++)
			if(num%i==0)
				if(isPrime(num/i)) 
					return num/i;
			
		return 1;
	}
	private static boolean isPrime(long num){
		for(long i=2;i<=(long)Math.sqrt(num);i++){
			if(num%i==0) return false;
		}
		return true;
	}
}

LargestPrimeFactorTest.java

public class LargestPrimeFactorTest {
	@Test
	public void testCalculate() {
		assertEquals(29, new LargestPrimeFactor(13195).calculate());
		assertEquals(6857,new LargestPrimeFactor(600851475143L).calculate());
	}
}