Best practice for passing many arguments to method?

Question

Occasionally , we have to write methods that receive many many arguments , for example :

public void doSomething(Object objA , Object objectB ,Date date1 ,Date date2 ,String str1 ,String str2 ) { } 

When I encounter this kind of problem , I often encapsulate arguments into a map.

Map<Object,Object> params = new HashMap<Object,Object>(); params.put("objA",ObjA) ;  ......  public void doSomething(Map<Object,Object> params) {  // extracting params   Object objA = (Object)params.get("objA");  ......  } 

This is not a good practice , encapsulate params into a map is totally a waste of efficiency. The good thing is , the clean signature , easy to add other params with fewest modification . what's the best practice for this kind of problem ?

Answer 1

In Effective Java, Chapter 7 (Methods), Item 40 (Design method signatures carefully), Bloch writes:

There are three techniques for shortening overly long parameter lists:

• break the method into multiple methods, each which require only a subset of the parameters
• create helper classes to hold group of parameters (typically static member classes)
• adapt the Builder pattern from object construction to method invocation.

For more details, I encourage you to buy the book, it's really worth it.