Fragmented - Android Developer Podcast

031: Effective Java - Item 8

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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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Stay tuned for more items from our "Effective Java for Android developers" Fragment series.

Show Notes
  • Effective Java (2nd Edition) - Joshua Bloch

    • 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.
            • Contact
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            • @donnfelker [twitter.com]
            • @kaushikgopal [twitter.com]
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