String Versus StringBuffer ?

An understanding of the difference between Java Strings and StringBuffers can lead to great performance increases. Although it may seem not to be the case given Java's String concatenation syntax (like a=a+"hi"), Strings are in actuality read-only (ie, immutable) after they are created so that they cannot change. As a result of this, when you concatenate Strings via the + operator, in the background a temporary StringBuffer gets created and the toString method is called on the StringBuffer to create the new String, and this operation is fairly time-consuming.

However, much less overhead is required to concatenate a String onto a StringBuffer object via the StringBuffer append method. You can basically think of each append as adding another String piece into a linked list that makes up the StringBuffer. So you basically have a StringBuffer consisting of a String chunk which then points to another String chunk which points to another String chunk, etc...

The benefits of StringBuffer become clear when you have a situation involving many concatenations. To illustrate this, let's try concatenating 10,000 "a" Strings together via the String + operator and via a StringBuffer append method and monitor the time required to perform these operations. The StringVersusStringBuffer class below illustrates this.

package test;

public class StringVersusStringBuffer {

         public static void main(String[] args) {

                 try {

                          final int NUM_REPEATS = 10000;

                          String string = "";

                          long start = System.currentTimeMillis();

                          for (int i = 0; i < NUM_REPEATS; i++) {

                                   string = string + "a";

                          }

                          long end = System.currentTimeMillis();

                          System.out.println("String loop time (ms): " + (end - start));

                          StringBuffer sb = new StringBuffer();

                          start = System.currentTimeMillis();

                          for (int i = 0; i < NUM_REPEATS; i++) {

                                   sb.append("a");

                          }

                          end = System.currentTimeMillis();

                          System.out.println("StringBuffer loop time (ms): " + (end - start));

                 } catch (Exception e) {

                          e.printStackTrace();

                 }

         }

}

OutPut :

String loop time (ms) : 156

StringBuffer loop time (ms) : 0