Java String test

Rumor spreads out that StringBuffer's operations is notably faster than String's.

Let's have some code String vs StringBuffer to see whether the rumor are true or not !

For quick text edit I always use VIM :

$ vim TestStringPerformance.java

Here comes the code:

import java.util.Date;

public class TestStringPerformance {
public static void main(String[] args) {
TestStringPerformance aString = new TestStringPerformance();
aString.testStringAppend(10000);
aString.testStringBufferAppend(10000);
aString.testStringAppend(10000);
aString.testStringBufferAppend(10000);

aString.testStringNew(10000);
aString.testStringBufferNew(10000);
aString.testStringNew(10000);
aString.testStringBufferNew(10000);

aString.testStringReplace5Chars(10000);
aString.testStringBufferReplace5Chars(10000);
aString.testStringReplace5Chars(10000);
aString.testStringBufferReplace5Chars(10000);
}

private void testStringAppend(int loopNum) {
Date startDate = new Date();
String prefixString = "A";
for (int i = 0; i< loopNum; i++) {
prefixString = prefixString + i;
}
Date endDate = new Date();
printTime("StringAppend", startDate, endDate);
}

private void testStringNew(int loopNum) {
Date startDate = new Date();
String newString;
for (int i = 0; i< loopNum; i++) {
newString = "B";
}
Date endDate = new Date();
printTime("StringNew", startDate, endDate);
}

private void testStringBufferAppend(int loopNum) {
Date startDate = new Date();
StringBuffer prefixString = new StringBuffer("A");
for (int i = 0; i< loopNum; i++) {
prefixString.append(i);
prefixString.toString();
}
Date endDate = new Date();
printTime("StringBufferAppend", startDate, endDate);
}

private void testStringBufferNew(int loopNum) {
Date startDate = new Date();
StringBuffer prefixString = new StringBuffer("A");
for (int i = 0; i< loopNum; i++) {
prefixString.replace(0,1,"B");
prefixString.toString();
}
Date endDate = new Date();
printTime("StringBufferNew", startDate, endDate);
}

private void testStringReplace5Chars(int loopNum) {
Date startDate = new Date();
String prefixString = "AAAAABBBBB";
for (int i = 0; i< loopNum; i++) {
prefixString = prefixString.replaceFirst("BBBBB", "BBBBB");
}
Date endDate = new Date();
printTime("StringReplace5Chars", startDate, endDate);
}

private void testStringBufferReplace5Chars(int loopNum) {
Date startDate = new Date();
StringBuffer prefixString = new StringBuffer("AAAAABBBBB");
for (int i = 0; i< loopNum; i++) {
prefixString.replace(0,5,"BBBBB");
prefixString.toString();
}
Date endDate = new Date();
printTime("StringBufferReplace5Chars", startDate, endDate);
}

private void printTime(String methodName, Date startDate, Date endDate) {
long millis = endDate.getTime() - startDate.getTime();
System.out.println(methodName + " took " + millis + " milliseconds ");
}
}

Now let's compile and run to see the result:

$ javac TestStringPerformance.java

$ java TestStringPerformance
StringAppend took 4047 milliseconds
StringBufferAppend took 656 milliseconds
StringAppend took 3235 milliseconds
StringBufferAppend took 656 milliseconds
StringNew took 0 milliseconds
StringBufferNew took 16 milliseconds
StringNew took 0 milliseconds
StringBufferNew took 0 milliseconds
StringReplace5Chars took 203 milliseconds
StringBufferReplace5Chars took 0 milliseconds
StringReplace5Chars took 32 milliseconds
StringBufferReplace5Chars took 0 milliseconds

$ java -version
java version "1.6.0_06"
Java(TM) SE Runtime Environment (build 1.6.0_06-b02)
Java HotSpot(TM) Client VM (build 10.0-b22, mixed mode, sharing)

So what ?
The answer is, On my PC and with JRE 1.6 update 6, StringBuffer is much faster than String on "Append" and "Replace" operations, but was slower on first initilization.

I ran the test again:

$ java TestStringPerformance
StringAppend took 3265 milliseconds
StringBufferAppend took 641 milliseconds
StringAppend took 3266 milliseconds
StringBufferAppend took 640 milliseconds
StringNew took 0 milliseconds
StringBufferNew took 16 milliseconds
StringNew took 0 milliseconds
StringBufferNew took 0 milliseconds
StringReplace5Chars took 93 milliseconds
StringBufferReplace5Chars took 0 milliseconds
StringReplace5Chars took 47 milliseconds
StringBufferReplace5Chars took 0 milliseconds

Somehow the time of "Replace" operation is changed: The String ran faster than the first time, whereas the StringBuffer is slower.
However, the final conclusion is the same :D .

What is the result on your PC?