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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019: Effective Java for Android developers : Item 4

Singer and Android developer Donn Felker explores Joshua Bloch’s fourth Item: Enforce noninstantiability with a private constructor.

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Show Notes:

Enforce noninstantiability with a private constructor.

Examples where you don’t want class to be instantiated

  1. class that groups static methods and static fields (Util like classes think java.lang.Math/java.util.Arrays)
  2. class that groups static methods (including factory methods) for objects implementing specific interfaces (think java.util.Collections)
  3. class that group methods on a final class (vs. extending the class)

Considerations

  • Makes no sense to instantiate such “Util” classes
  • Private constructors prevent instantiation
  • Important side effect: prevents subclassing

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018: Effective Java for Android developers : Item 3

In this mini Fragment, we introduce Joshua’s third Item: Enforce the Singleton property with a private constructor or an enum type.

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Show Notes:

Enforce the Singleton property with a private constructor or an enum type

Approaches

  1. Create a public static final INSTANCE variable and privatize constructor
  2. Same as 1 but privatize variable and expose access with provide factory method getInstance
  3. Single element Enums

Considerations

  • First two approaches are open to Serialization attacks (deserializing creates new instance)
  • To protect from those declare the fields transient + provide readResolve method
  • Enums are concise, provide free serialization and ironclad Singleton guarantees and are functionally equivalent to first approach

Supplemental reading (for the diligent ones that follow shownotes)

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