Find the difference between the sum of the squares of the first n natural numbers and the square of the sum.

SumSquareDiff.java

public class SumSquareDiff {
	public static long calculate(int n){
		int sum_of_sq=0;
		int sum=0;
		for(int i=1;i<=n;i++){
			sum+=i;
			sum_of_sq+=i*i;
		}
		return sum*sum-sum_of_sq;
	}
}

SumSquareDiffTest.java

public class SumSquareDiffTest {
	@Test
	public void testCalculate() {
		assertEquals(2640, SumSquareDiff.calculate(10));
		assertEquals(25164150, SumSquareDiff.calculate(100));
	}
}