[Java] Performance Tuning

Performance Tuning:

• Know How:
  • Designing for Performance
    • Avoid Creating Objects.
      • Generally speaking, avoid creating short-term temporary objects if you can. Fewer objects created mean less-frequent garbage collection, which has a direct impact on user experience.
    • Performance Myths
      • It was cheaper to invoke methods on a HashMap map than a Map map,
    • Prefer Static Over Virtual
      • If you don't need to access an object's fields, make your method static. Invocations will be about 15%-20% faster. It's also good practice, because you can tell from the method signature that calling the method can't alter the object's state.
    • Use Static Final For Constants
      • We can improve matters with the "final" keyword: static final String strVal = "Hello, world!"; instead of static String strVal = "Hello, world!";
      • strVal will use a relatively inexpensive "string constant" instruction instead of a field lookup.
    • Use Enhanced For Loop Syntax
      • Algorithm Performance C > B > A. Ex: A. 在for loop用length. B. 不在for loop用length, 用local variable存length. C. 用Foo a : mArray.
    • Avoid Enums Where You Only Need Ints
    • Use Package Scope with Inner Classes
    • Use Floating-Point Judiciously
    • Know And Use The Libraries
      • Ex: String.indexOf
    • Use Native Methods Judiciously
  • Use StringBuilder to improve string editing performance.
  • 不再使用的物件要盡早設定為 null，以便早點被當成垃圾清掉。
  • Use global variable to reuse memory.
• Reference:
  • http://developer.android.com/guide/practices/design/performance.html
  • http://www.oreilly.com.tw/column_sleepless.php?id=j005
  • http://blog.javia.org/android-allocation-free-code-avoids-the-gc-freeze/
  • http://j2se.myweb.hinet.net/article/java/010.htm