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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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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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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016: Effective Java for Android developers : Item 2

In our third Fragment installment, we introduce Josh’s second Item: Consider a builder when faced with many constructor parameters.

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Consider a builder when faced with many constructor parameters

Telescoping Constructor Pattern

  • Provide constructor with only required parameters, another with a single optional param, a third with 2 optional params… and so on.
    • Advantage: Works well for small number of parameters
    • Disadvantage: Does NOT scale well

JavaBeans Pattern

  • Call parameterless constructor to create the object; then call setter methods to set required parameter and each optional param of interest.
    • Advantage: Scales well, easy (but wordy) to read resulting code
    • Disadvantage: Allows inconsistency (if all required params not called); impossible to make classes immutable if using this pattern.

Builder pattern

  • winner!
    • Advantage: Simulates named optional parameters; allows immutable objects to be constructed; flexible
    • Disadvantage: more ceremony to actually construct the Builder Class and finally use.

Example usage from Android source:

Tip:

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