Java Concurrency (&c)

One thing I have noticed among Java API users is that some don't seem to know that there is a difference between StringBuffer and StringBuilder. There is: StringBuffer is synchronized, and StringBuilder isn't. (The same is true for Vector and ArrayList, as well as Hashtable and HashMap). StringBuilder avoids extra locking operations, and therefore you should use it where possible. That's not the meat of this post, though. Among those who know that StringBuffer is synchronized, they sometimes think that it has magical thread-safety properties. Here's a simplified version of some code I wrote recently final StringBuilder sb = new StringBuilder(); Runnable runner = new Runnable() { @Override public void run() { sb.append("1"); } }; Thread t = new Thread(runner); t.start(); try { t.join() } catch (InterruptedException e) {} // use sb. A fellow looked at this code, and said that he thought I should use StringBuffer, because it is safer with multiple th...

In my last post, I made an offhand reference to the fact that object constructors are worthless in Java. I was asked why this is, so I thought I'd fill in the details. This topic is a little more well-understood by the developer community than some of the concurrency tidbits that I usually discuss. People who use dependency injection toolkits like Guice and Spring 's inversion of control tend to have very strong feelings on the advanced suckitude of constructors. I know quite a few developers who claim that use of Guice changed the way they code (for the better). ETA: I've had a few people tell me just to use SPI. The point of this post is not that DI is wonderful, it is that constructors are awful. SPI doesn't stop constructors from being awful. In fact, it is yet another horrible solution, what with all of those Foo and FooImpl classes. If you like SPI, go ahead and use it. Furthermore, neither DI nor SPI addresses two of the three issues I mentioned. So, wi...