1. In JDK5, Annotation is introduced. Annotation just simplify programming, not for performance raising

  2. DD(deployment description) over Annotation

  3. CoC, Convention over Configuration

  4. DRY, Don’t Repeat Yourself

  5. heap size vs. GC

    • big heap size : GC less frequent, slower(a lot of memory to search through)  
    • small: GC more frequent, fast

  6. ArrayList.toArray(new xxx[0]), 参数用零长度相应Java对象的数组即可。