Using character instead of String for single-character values in StringBuffer append

Question

I was going through the PMD rule AppendCharacterWithChar. It says Avoid concatenating characters as strings in StringBuffer.append.

StringBuffer sb = new StringBuffer();
  // Avoid this
  sb.append("a");

  // use instead something like this
  StringBuffer sb = new StringBuffer();
  sb.append('a');

Do I really need this PMD rule? Is there much performance difference between the following two piece of code?

String text = new StringBuffer().append("some string").append('c').toString();

String text = new StringBuffer().append("some string").append("c").toString();

Answer 1

Appending a character as a char will always be faster than appending it as a String.

But does the performance difference matter? If you just do it once, it doesn't. If it is inside a cycle repeating its body a million times, then yes, it might matter.

If you already have the character at compile time, just append it as a character. If it is stored in a variable with String type, don't bother accessing it e.g. with String.charAt(0) or some other ways, simply just append the String.

On a Side Note:

Favor the StringBuilder class to StringBuffer. StringBuilder is faster because its methods are not synchronized (which you don't need in most cases).

On a Side Note #2:

This won't compile:

String text = new StringBuffer().append("some string").append('c');

append() returns StringBuffer for chaining. You need to call toString() on it:

String text = new StringBuffer().append("some string").append('c').toString();