java - How compute elapsed time encrypt and decrypt algorithm?

for (int ii = 0 ; ii < 200 ; ii++)
    {
     encrypt();    
    }

long start = System.currentTimeMillis();
    for (int ii = 0 ; ii < 2000 ; ii++)

    {
     encrypt();    
    }
long elapsed = System.currentTimeMillis() - start;

for (int ii = 0 ; ii < 200 ; ii++)
    {
     decrypt();    
    }


long start = System.currentTimeMillis();
    for (int ii = 0 ; ii < 2000 ; ii++)
    {
     decrypt();    
    }
long elapsed = System.currentTimeMillis() - start;



private void encrypt()

    {
            M = new BigInteger(64,random);
            C = M.multiply(k).mod(N);  
    }

private void decrypt()
    {
            kk= k.modinverse(N); 
            Mp = kk.multiply(c).mod(N); 
    }

But I feel that the results are incorrect when run this program on netbeans platform.
Is there way to compare any two algorithm cryptography under execution time .
Is necessary decrypt algorithm take long time than encrypt algorithm?
Please any suggest.