java keywords 关键字

Java Language Specification 中的关键字列表：
http://docs.oracle.com/javase/specs/jls/se7/html/jls-3.html#jls-3.9

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3.9 Keywords
50 character sequences, formed from ASCII letters, are reserved for use as keywords and cannot be used as identifiers (§3.8).:
Keyword: one of
    abstract   continue   for          new         switch
    assert     default    if           package     synchronized
    boolean    do         goto         private     this
    break      double     implements   protected   throw
    byte       else       import       public      throws
    case       enum       instanceof   return      transient
    catch      extends    int          short       try
    char       final      interface    static      void
    class      finally    long         strictfp    volatile
    const      float      native       super       while               
       
The keywords const and goto are reserved, even though they are not currently used. This may allow a Java compiler to produce better error messages if these C++ keywords incorrectly appear in programs.

While true and false might appear to be keywords, they are technically Boolean literals (§3.10.3). Similarly, while null might appear to be a keyword, it is technically the null literal (§3.10.7).

transient，volatile：
http://stackoverflow.com/questions/106591/do-you-ever-use-the-volatile-keyword-in-java?rq=1

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When is volatile enough?

If two threads are both reading and writing to a shared variable, then using the volatile keyword for that is not enough. You need to use synchronization in that case to guarantee that the reading and writing of the variable is atomic.

But in case one thread reads and writes the value of a volatile variable, and other threads only read the variable, then the reading threads are guaranteed to see the latest value written to the volatile variable. Without making the variable volatile, this would not be guaranteed.

Performance considerations of using volatile:

Reading and writing of volatile variables causes the variable to be read or written to main memory. Reading from and writing to main memory is more expensive than accessing the CPU cache. Accessing volatile variables also prevent instruction reordering which is a normal performance enhancement technique. Thus, you should only use volatile variables when you really need to enforce visibility of variables.