"StringBuffer" and "String" quality competition

Read cherami wrote "String or StringBuffer?" Behind the number of netizens, as well as the comments, I feel this issue is necessary to properly investigate, prepared a simple test category and a script to run it. Laws passed that test parameters for different categories, and in different JDK testing discovered the problem really is a very interesting question. Let's get started.

First step in the preparatory work

In order to facilitate the work of the latter test, it is necessary to prepare a simple script:

Echo test by jdk1.2.2/opt/java/jdk1.2.2/bin/javac StringTest.java/opt/java/jdk1.2.2/bin/java StringTestecho test by jdk1.3.1_09/opt/java/jdk1.3.1_09 / bin / javac StringTest.java/opt/java/jdk1.3.1_09/bin/java StringTestecho test by jdk1.4.2/opt/java/jdk1.4.2/bin/javac StringTest.java/opt/java/jdk1.4.2/bin / java StringTest

According to the above script needs can be applied to windows or linux, I conducted tests in linux, so I kept it as a document stringtest.sh, if you windows on the test, you can save for stringtest.bat.

Note: In this paper, the results are running behind the continuous operation and many of them take a more typical sample and the average value)

The second step, began to write code

The first I almost did not consider how to write the following code:

Public class StringTest (public static void main (String [] args) (long start = System.currentTimeMillis (); for (int i = 0; i <10000; i + +) (String s = "This is a" + "long test string for the "+" different JDK performance "+" testing. ";) long end = System.currentTimeMillis (); System.out.println (" Directly string contact: "+ (end-start)); start = System.currentTimeMillis (); for (int i = 0; i <10000; i + +) (StringBuffer buffer = new StringBuffer (); buffer.append ( "This is a"); buffer.append ( "long test string for"); buffer. append ( "different JDK performance"); buffer.append ( "testing."); String ss = buffer.toString ();) end = System.currentTimeMillis (); System.out.println ( "StringBuffer contact:" + ( end-start));))

The result:

Test by jdk1.2.2Directly string contact: 0StringBuffer contact: 120test by jdk1.3.1_09Directly string contact: 1StringBuffer contact: 47test by jdk1.4.2Directly string contact: 0StringBuffer contact: 53

Oh, is not a big accident? ! ! ! I also started, but Do not, in fact I made a mistake, as a result of the string + direct operation of the string are, in the compiler to compile time optimization, String s = "This is a" + "long test string for the" + "different JDK performance" + "testing."; compiled after a fact: String s = "This is a long test string for different JDK performance testing.";, Oh, this is a simple assignment, and no wonder the time spent almost no.

The third step is to amend the code

Public class StringTest (public static void main (String [] args) (String s1 = "This is a" String s2 = "long test string for" String s3 = "different JDK performance" String s4 = "testing." ; long start = System.currentTimeMillis (); for (int i = 0; i <10000; i + +) (String s = s1 + s2 + s3 + s4;) long end = System.currentTimeMillis (); System.out.println ( "Directly string contact:" + (end-start)); start = System.currentTimeMillis (); for (int i = 0; i <10000; i + +) (StringBuffer buffer = new StringBuffer (); buffer.append (s1 ); buffer.append (s2); buffer.append (s3); buffer.append (s4); String ss = buffer.toString ();) end = System.currentTimeMillis (); System.out.println ( "StringBuffer contact : "+ (end-start));))

The result:

Test by jdk1.2.2Directly string contact: 140StringBuffer contact: 123test by jdk1.3.1_09Directly string contact: 32StringBuffer contact: 21test by jdk1.4.2Directly string contact: 48StringBuffer contact: 37

Looking at the results from the above we really can be "use String or StringBuffer?" In the conclusions, but also can see the different versions of the JDK performance difference is quite large, the performance of the worst JDK1.2.2 and JDK1. 3.1 the best performance.

The end of the discussion? Oh, Buyaoji, it is far from ending. :)

The fourth step is to reduce cycle times (from 10,000, a 1000)

Public class StringTest (public static void main (String [] args) (String s1 = "This is a" String s2 = "long test string for" String s3 = "different JDK performance" String s4 = "testing." ; long start = System.currentTimeMillis (); for (int i = 0; i <1000; i + +) (String s = s1 + s2 + s3 + s4;) long end = System.currentTimeMillis (); System.out.println ( "Directly string contact:" + (end-start)); start = System.currentTimeMillis (); for (int i = 0; i <1000; i + +) (StringBuffer buffer = new StringBuffer (); buffer.append (s1 ); buffer.append (s2); buffer.append (s3); buffer.append (s4); String ss = buffer.toString ();) end = System.currentTimeMillis (); System.out.println ( "StringBuffer contact : "+ (end-start));))

The result: