Effective Java 3/E summary chanpter 2 (Shorter version)

28 Dec 2020

Chanpter 2 : Methods Common to All Objects

Item 10

You can find the longer version of this summary here.

equals

• Should it be implemented?
• Is it an inherited class?
• Implement hashCode

implementation method

The equals method implements an equivalence relation (Reflexive, Symmetric, Transitive, Consistent), null check and Liskov subsitution principle

• Determine whether you are yourself with ==
• Check type with instanceOf
• Type casting
• Check the ‘Core’ field
  • in the order of the probability of being different and the fastest comparison

hashCode

• If equals is true, hashCode is always true. If equals is false, hashCode is not always false
• Generate hash code with fields of equals.
• Don’t publish rules for generating hash code.

toString

• Ideally, it should be a string that perfectly describes the object itself.
• Return all key information the object has.

Cloneable

• Don’t implement Cloneable. Instead, implement a copy factory, a copy constructor.

  Copy constructor

  public Yum(Yum yum) { ... };
  

  Copy factory

  public static Yum newInstance(Yum yum) { ... };
  

Comparable

• Like equals, Reflexive, Symmetric and Transitive must be met.
  • An inherited object cannot implement a perfect compareTo.
• Sorted collections use compareTo() for equality comparison.
• Don’t use relational operators (<, >), use static compare methods or comparators.