Effective Java(1)

Item1: consider static factory methods instead of constructors

advantages:

• They have names

• They not required to create a new object each time they are invoked

  (allows immutable classes to use preconstructed instances or to cache instances as they are constructed)

• They can return an object of any subtype of their return type

• The class of the returned object can vary from call to call as a function of the input parameters

• The class of the returned object need not exist when the class containing the method is written

 

shortcomming:

• Classes without public or protected constructors cannot be subclassed

• Hard for programmers to find

 

sum-up: first consider static factories before providing public constructors

 

Item 2: consider a builder when faced with many constructor parameters

The builder›s setter methods return the builder itself(return this) so that invocations can be chained, resulting in a fluent API

 

when-to-use: when you have more than a handful of optional parameters

 

Item 3: enforce the singleton property with a private constructor or an enum type

 

Item 4 : enforce noninstantiability with a private constructor

 

Item 5: prefer dependency injection to hardwiring resources

 

Item 6: avoid creating unnecessary objects