Why a synchronized StringBuffer was never a good idea

Introduction

StringBuffer is a synchronized class for mutable strings.  The main problem with making it synchronized is that

  1. It was usually used as a local variable so making it synchronized just made it slower.
  2. It was never a good idea to use it in a multi-threaded way.  This problem is that developers assumed that methods which used StringBuffer were themselves thread safe when they were not.

 

The problem with StringBuffer

This is an example from a real class which is used in production in many trading systems. It’s not a commonly used but you might assume that StringBuffer gives you thread safety, when it doesn’t.

public void addProperty(String name, String value) {
        if (value != null && value.length() > 0) {
            if (sb.length() > 0) {
                sb.append(',');
            }
            sb.append(name).append('=').append(value);
        }
    }
While individual calls are thread safe, multiple calls are not.  It is almost impossible to find a good use for StringBuffer that doesn’t involve multiple calls (including toString)

A puzzle

Imagine three threads call (in no particular order)
 T1: addProperty("a", "b");
T2: addProperty("c", "d");
T3: sb.toString();

write a program which will generate every possible output of T3′s sb.toString() I found 89.  With thread safety, you might reduce this to 4.

Note

If you used StringBuilder it would be worse, but at least you might not assume your method is thread safe when it is not. e.g. SimpleDateFormat uses StringBuffer

 

Related Whitepaper:

Bulletproof Java Code: A Practical Strategy for Developing Functional, Reliable, and Secure Java Code

Use Java? If you do, you know that Java software can be used to drive application logic of Web services or Web applications. Perhaps you use it for desktop applications? Or, embedded devices? Whatever your use of Java code, functional errors are the enemy!

To combat this enemy, your team might already perform functional testing. Even so, you're taking significant risks if you have not yet implemented a comprehensive team-wide quality management strategy. Such a strategy alleviates reliability, security, and performance problems to ensure that your code is free of functionality errors.Read this article to learn about this simple four-step strategy that is proven to make Java code more reliable, more secure, and easier to maintain.

Get it Now!  

2 Responses to "Why a synchronized StringBuffer was never a good idea"

  1. Alexander Stepanov says:

    >While individual calls are thread safe, multiple calls are not.

    It would be better for understanding to name them not multiple but chained calls.

Leave a Reply


9 − nine =



Java Code Geeks and all content copyright © 2010-2014, Exelixis Media Ltd | Terms of Use | Privacy Policy
All trademarks and registered trademarks appearing on Java Code Geeks are the property of their respective owners.
Java is a trademark or registered trademark of Oracle Corporation in the United States and other countries.
Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation.

Sign up for our Newsletter

20,709 insiders are already enjoying weekly updates and complimentary whitepapers! Join them now to gain exclusive access to the latest news in the Java world, as well as insights about Android, Scala, Groovy and other related technologies.

As an extra bonus, by joining you will get our brand new e-books, published by Java Code Geeks and their JCG partners for your reading pleasure! Enter your info and stay on top of things,

  • Fresh trends
  • Cases and examples
  • Research and insights
  • Two complimentary e-books