[JAVA] Effective JAVA - Item 2 : Consider a builder when faced with many constructor parameters

Case : scale well to large numbers of optional parameters

-> static factories and contructors not good for this case

 

then how to solve this case?

 

The answer is : Builder

 

Traditionally programmers have used the 'telescoping constructor'

but, there have some problem

•  Hard to write client code
• Harder to read it

 

and also you can say 'how about use JavaBeans'

but there are still have some issues.

• Inconsistent state partway through its construction
• Precludes the possibility of making as class immutable

 

Luckily, there is the 'Builder pattern'

 

Let's see how it works

1. Client calls a constructor with all of the required parameters and gets a builder object
2. Client calls setter-like methods on the builder object to set each optional parameter of interest
3. The client calls a parameterless build method to generate the object, which typically immutable

Advantages of Builder pattern

• Simulates named optional parameters
• Well suited to class hierarchies

Summary

The builder pattern is a good choice when designing classes whose constructors or static factories would have more then a handful of parameters