Question

I am manipulating ssn.
Input =”123456789″
Output=”896745123″

You take the first 3 digits from the input (i.e 123) and swap it with the last two digits “89” and then swap “45” with “67”. Below is the code I have using toCharArray. But I didn’t like it. This method (not the test) can be accessed by many users at a time. I was looking for a better in performance, readability and trade safe solution.

I appreciate your help.

@Test
    public void testSSNString(){

        String original="123456789";
        String result="896745123";
        char[] charResult=original.toCharArray();

        char temp=charResult[6];
        charResult[6]=charResult[0];
        charResult[0]=charResult[7];
        charResult[7]=charResult[1];
        charResult[1]=charResult[8];
        charResult[8]=charResult[2];
        charResult[2]=charResult[5];
        charResult[5]=charResult[4];
        charResult[4]=charResult[3];
        charResult[3]=temp;

        assertEquals(original.toCharArray(),charResult);

    }

Answer 1

The way that you have given is essentially the best you can do in Java in terms of performance. Using arrays is faster than using StringBuilder.

To improve readability, I would just make some small changes, like making a new array for the permuted output:

@Test
public void testSSNString() {
  String original = "123456789";
  String expected = "896745123";

  char[] in = original.toCharArray();
  char[] out = new char[9];
  out[0] = in[7];
  out[1] = in[8];
  out[2] = in[5];
  out[3] = in[6];
  out[4] = in[3];
  out[5] = in[4];
  out[6] = in[0];
  out[7] = in[1];
  out[8] = in[2];

  assertEquals(expected.toCharArray(), out);
}