Hidden Features of Java

Java.util.concurrent is one of the most attractive features of java for server programming. ConcurrentHashMap is faster, cleaner and much easier to use than locking every time you need a access a shared HashMap. Not only that but it doesn't lock the entire hash, just a partition of what ever you will be accessing.<p>Also AtomicInt,Float,Long make life easier when dealing with threaded programs.

&#62;closed as not constructive by Robert Harvey♦ Oct 5 '11 at 5:49<p>&#62;This question is not a good fit to our Q&#38;A format. We expect answers to generally involve facts, references, or specific expertise; this question will likely solicit opinion, debate, arguments, polling, or extended discussion.<p>I appreciate StackOverflow's active moderators, but this question was actually pretty interesting. What harm would it do to let the question open?

<a href="http://monocaffe.blogspot.com/2011/10/javas-ghost-jvms.html" rel="nofollow">http://monocaffe.blogspot.com/2011/10/javas-ghost-jvms.html</a><p>"how does tools like JPS, JConsole or VisualVM know the JVMs running in a system? They simply look in the folder /tmp/hsperfdata_foo where a 32KB data file with the PID as name is created for each JVM."<p>Not a hidden feature of Java, but of Sun's (Oracle) JVM which I'm not sure if happens in other JVMs but it's kind of useful for doing different stuff.

The example in the linked ThreadLocal documentation appears to have a mistake.<p>In getCurrentThreadId it should read<p>return uniqueNum.get();<p>not<p>return uniqueId.get();

My preferred initialization for lists of strings (shorter than the anon class + instance init e.g.)<p><pre><code> List&#60;String&#62; fruits = Arrays.asList("apple,orange,pear".split(","));</code></pre>