Performance Comparison of String and StringBuffer

Java Tutorials - Herong's Tutorial Examples

∟Performance Comparison of String and StringBuffer

This section provides a tutorial example to do a performance comparison of 3 classes: String, StringBuffer, SimpleStringBuffer.

One main reason of using the StringBuffer class instead of the String class is that StringBuffer performs much better in joining strings together. In order to confirm this, I wrote the following tutorial example to compare performances of 3 classes: String, StringBuffer, and SimpleStringBuffer:

/* StringBufferTest.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
public class StringBufferTest {
   public static void main(String[] args) {
      int l = 128;
      long t1 = 0;
      long t2 = 0;
      String s = null;
      System.out.println("Initial capacity = "+l);
      for (int i=1; i<=3; i++) {
         System.out.println("Test: "+i);
         t1 = System.currentTimeMillis();
         if (i==1) s = stringTest(l);
         else if (i==2) s = stringBufferTest(l);
         else if (i==3) s = simpleStringBufferTest(l);
         t2 = System.currentTimeMillis();
         System.out.println("   Final string = "+s);
         System.out.println("   Total time = "+(t2-t1));
      }
   }
   public static String stringTest(int l) {
      String s = null;
      for (int i=0; i<100000; i++) {
         String sb = "0";
         sb = sb+"01";
         sb = sb+"012";
         sb = sb+"0123";
         sb = sb+"01234";
         sb = sb+"012345";
         sb = sb+"0123456";
         sb = sb+"01234567";
         sb = sb+"012345678";
         sb = sb+"0123456789";
         s = sb;
      }
      return s;
   }
   public static String stringBufferTest(int l) {
      String s = null;
      for (int i=0; i<100000; i++) {
         StringBuffer sb = new StringBuffer(l);
         sb = sb.append("0");
         sb = sb.append("01");
         sb = sb.append("012");
         sb = sb.append("0123");
         sb = sb.append("01234");
         sb = sb.append("012345");
         sb = sb.append("0123456");
         sb = sb.append("01234567");
         sb = sb.append("012345678");
         sb = sb.append("0123456789");
         s = sb.toString();
      }
      return s;
   }
   public static String simpleStringBufferTest(int l) {
      String s = null;
      for (int i=0; i<100000; i++) {
         SimpleStringBuffer sb = new SimpleStringBuffer(l);
         sb = sb.append("0");
         sb = sb.append("01");
         sb = sb.append("012");
         sb = sb.append("0123");
         sb = sb.append("01234");
         sb = sb.append("012345");
         sb = sb.append("0123456");
         sb = sb.append("01234567");
         sb = sb.append("012345678");
         sb = sb.append("0123456789");
         s = sb.toString();
      }
      return s;
   }
}

I compiled and ran the program with JDK 20. Here is the result:

Initial capacity         128

StringTest                92
StringBufferTest          61
SimpleStringBufferTest    78

I compiled and ran the program with JDK 13. Here is the result:

Initial capacity         128

StringTest               187
StringBufferTest          47
SimpleStringBufferTest    78

Below is the result with JDK 8 on an older computer:

Initial capacity         128

StringTest               132
StringBufferTest          49
SimpleStringBufferTest    47

Below is the result with JDK 1.4 on an older computer:

Initial capacity           16     32     64    128

StringTest               1973   1963   1963   1963
StringBufferTest          631    571    500    551
SimpleStringBufferTest    671    611    521    630

The result shows that:

The StringBuffer class does perform much better than the String class. The StringBuffer is about 3 times faster!
The SimpleStringBuffer class, my implementation of a string buffer class, performs almost the same as the StringBuffer class!