Effective Java Reloaded

Effective Java reloaded

Forward

• Grammar
• Vocabulary
• Idiom

List

47, 8, 9, 10, 36, 38 (re-read) 48, 39, 15, 41, 49, 45, 43

15. Minimize mutability

Recipe

• Don't provide mutators
• Ensure the class can't be extended (final and private constructors)
• Make all fields final
• Make all fields private
• Ensure exclusive access to any mutable components (defensive by copying)

Advantage

• Simple
• Inherently thread-safe
• Can be shared freely
• Can share internals

=> persistent data structure

Cons

• Require separate object for each distinct value

49. Prefer primitive types to boxed primitives

Primitives vs. Reference type

• Values vs. Values + Identities
• Only funcation values vs. one nonfunctional value (has null)

• time / space efficiency vs. < time /space efficiency

When to use boxed primitives

• when API requires it, generics, collection elements etc

41. Use overloading judiciously

• Never export two overloadings with same number of parameters

8. Obey the general contract when overriding equals

Know when not to override

• Inherently unique instances (e.g. thread)
• 'logical equality' unimportant (e.g. random)
• superclass does the right thing (e.g. collections)
• equals will never be invoked (e.g. private class)
• singletons (also enums)

Contract

• reflexivity
• symmetry
• transitivity
• consistency
• non-nullity

You cannot extend an instantiable class and add a value component while preserving the equals contract! => use composition instead of inheritance

Use Guava for equals

public class Person {
  final String name, nickname;
  final Movie favMovie;

  @Override public boolean equals(Object object) {
    if (object == this)
      return true;
    if (object instanceof Person) {
      Person that = (Person) Object;
      return Objects.equal(this.name, that.name)
        && Objects.equal(this.nickname, that.nickname)
        && Objects.equal(this.favMovie, that.faveMovie);
    }
    return false;
  }
  ...
}

On Java 7, Objects is available (No need for Guava)

9. hashcode

General contract

• Calling hashCode on same object, same JVM , must return the same integer
• if two objects are equal must return same integer on each object

How to implement

• Want uniform distribution
• refer to book for detail
• or use Guava return Objects.hashCode(areaCode, prefix, lineNumber);