Performance difference of using String.intern(), Compare by Reference & Compare by Value - Part 2 / 2

Continued from "Performance difference of using String.intern(), Compare by Reference & Compare by Value - Part 1 / 2", let’s go further on the captioned topic.

How about the cost of applying String.intern()?

Let’s take a look of the following sample code:

public class Test3 {           public void instantiateNoIntern(){          long start = System.nanoTime();          String a = "ABCDEFGHIJKLMNOPQRSTUV";          String b = new String("ABCDEFGHIJKLMNOPQRSTUV");          long end = System.nanoTime();          System.out.println("Elapsed Time (ns): " + (end - start) );      }      public void instantiateWithIntern(){          long start = System.nanoTime();          String a = "ABCDEFGHIJKLMNOPQRSTUV";          String b = new String("ABCDEFGHIJKLMNOPQRSTUV").intern();          long end = System.nanoTime();          System.out.println("Elapsed Time (ns): " + (end - start) );      }           public static void main(String[] args){                   Test3 test = new Test3();          System.out.println("Instantiation cost NO String.intern() : ");          for (int i = 10; i > 0 ; i--){               test.instantiateNoIntern();          }                   System.out.println("");          System.out.println("Instantiation cost with String.intern() : ");          for (int i = 10; i > 0 ; i--){               test.instantiateWithIntern();          }      }      }

The execution result is shown below:

Instantiation cost without String.intern() : Elapsed Time (ns): 3622 Elapsed Time (ns): 603 Elapsed Time (ns): 302 Elapsed Time (ns): 302 Elapsed Time (ns): 302 Elapsed Time (ns): 302 Elapsed Time (ns): 0 Elapsed Time (ns): 302 Elapsed Time (ns): 301 Elapsed Time (ns): 301 Instantiation cost with String.intern() : Elapsed Time (ns): 2113 Elapsed Time (ns): 604 Elapsed Time (ns): 604 Elapsed Time (ns): 302 Elapsed Time (ns): 905 Elapsed Time (ns): 604 Elapsed Time (ns): 604 Elapsed Time (ns): 604 Elapsed Time (ns): 604 Elapsed Time (ns): 603

 Here is the result summary:

	Total Time (nanosecond)
Without applying String.intern()	6,337
Has been applying String.intern()	7,547
Difference for 100 operations	1,210

From the result above, we can see that the cost for applying intern() is very low in actual which means intern() is still worth for applying as the time saved by alternatively using Compare by Reference is significant.


Let’s integrate this result with the tables before to get an overall view:

	Total Time (nanosecond)			Result Correctness
	Comparison operation	Instantiation	Comparison Operation + Instantiation
Before using String.intern()
By Reference	2,416	6,337	8,753	Incorrect
By Value	49,203	6,337	55,540	Correct
After using String.intern()
By Reference	2,415	7,547	9,962	Correct
By Value	6,943	7,547	14,490	Correct

Remarks
By Reference:  ==
By Value:          .equals()


Hope this article is interesting to you and hope you enjoy it!