031: Effective Java for Android Developers – Item #8

In this mini Fragment, we introduce Joshua’s eighth Item. This one is a doozy, probably one of the longest items in the group of the effective Java series, but most definitely quite important.

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Show Notes

Obey the general contract when overriding equals

When to not override equals:

  • Each instance of the class is inherently unique.
  • You don’t care whether the class provides a “logical equality” test.
  • A superclass has already overridden equals, and the superclass behavior is appropriate for this class.

The equals method implement an equivalence relation which states it must be:

  • Reflexive
  • Symmetric
  • Transitive
  • Consistent
  • For any non-null reference x, x.equals(null) must return false.

A recipe for a high-quality equals method is as such:

  • Use the == operator to check for references to this object.
  • Use the instanceof operator to check if the argument has the correct type¬†
  • Cast to the correct type.
  • Check all field types and corresponding field types.
  • Finally, when done, ask yourself – is this method symmetric, transitive and consistent?

Caveats

  • Always override hashcode when you override equals
  • Don’t be too clever!
  • Don’t substitute another type for Object in the equals declaration.

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029: All about the infamous 65,536 dex method count

If you’ve been an Android developer in the last 2 years, you must have seen this dreaded exception: dex: method ID not in [0, 0xffff]: 65536

Quick googling would immediately bring up the phrase “65K method count” and the recommended solution “multi-dexing”. But if you want to really understand this mysterious number and the reason behind its existence, listen on!

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Show Notes

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025: Effective Java for Android developers : Item 7

In this mini Fragment, we introduce Joshua’s seventh Item and a momentous end to the first chapter: Avoid finalizers

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Show Notes

Avoid finalizers

  • If you don’t know what they are, ignorance is bliss. If you know what they are, avoid them!
  • Finalizers in Java != destructors in C++ (C++ counterparts to constructors).
  • In C++ destructors
    • you reclaim resources here (Java has GC)
    • you also reclaim non-memory resources (use the try-finally block in Java)
  • (unpredicatable amt of time between object becoming unreachable and finalizer being executed) Never do anything time critical in finalizer!
    • System.gc + System.runFinalization increase chances – no guarantee
    • System.runFinalizersOnExit + Runtime.runFinalizersOnExit are the ones that do – but they are fatally flawed
  • Java 7 has try with resources, which is also interesting and auto-closeables. [Android] devs can only dream of these.
  • If an uncaught exception is thrown in a finalizer, it is ignored, and the finalization abruptly terminates.
  • Severe performance penalty for using finalizers – (one e.g.) time to create and destroy simple object goes from 5.6ns -> 2400ns
  • Only valid use: as a safety net or to terminate noncritical native resources.
  • [Android] you’re probably better off using Android’s lifecycle methods.

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024: Effective Java for Android developers : Item 6

Joshua’s sixth Item: Eliminate obsolete object references, in a distinctively croaky voice.

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Show Notes

Eliminate obsolete object references

Supplemental reading (for the diligent ones that follow shownotes)

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022: Effective Java for Android developers : Item 5

In this mini Fragment, we introduce Joshua’s fifth Item: Avoid creating unnecessary objects.

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Show Notes

Avoid creating unnecessary objects

Snippet to demonstrate AutoBoxing problems

// sum of all positive values
Long sum = 0L;
for (long i=0; i< Integer.MAX_VALUE; i++) {
  sum+=i;
}

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