Java Design Patterns – Naming the Pattern for Passing One Object to a Constructor

design-patternsjavanamingobject-orientedterminology

If you have a constructor that takes a lot of parameters, like this:

  public OrgUnitsHalRepresentation(List<OrgUnitSummaryHalRepresentation> orgUnitSummaryHalRepresentationList,
  int count, int providedCount, int total, int page, int filterLimit, boolean hasNextPage, boolean isDefaultCount)

You can use a separate class that takes nothing in the constructor and set these parameters using setters and pass in this into the constructor instead:

public OrgUnitsHalRepresentation(Pagination(Name of pattern) p)

Does this have a name so that I can use it in my class name?

Best Answer

This is the Parameter Object Design Pattern (or Argument Object), the related Refactoring is called Introduce Parameter Object.

Related Solutions

Java – Constructor vs setter validations

Your class allows someone to say myProject.setName(null), avoiding the null check in the constructor. If you want to set stuff through the constructor but need checks (question 2), I suggest doing the checks in set-methods and call those from the constructor. Example:

public class Project {

    private int id;
    private String name;  

    public Project(int id, String name, Date creationDate, int fps, List<String> frames) {
        setName(name);
        setId(id);
    }

    public void setId(int id) { 
        if(id == 0 ){
            throw new IllegalArgumentException("id can't be zero");
        }
        this.id = id;
    }

    public void setName(String name) {
        if(name == null ){
            throw new NullPointerException("Name can't be null");
        }
        this.name = name;
    }

}

This avoids code duplication.

Object-oriented – does this model-pattern have a name

That is an OOP Data Descriptor. Although you are describing additional information about a class rather than information about bits in memory, the fundamental parity still applies; you're describing in one place useful aspects about data in another place.

I'd advise you to adopt that name, write up a clearer definition of the pattern, and use the name in code. ("Type" already means something in PHP, so you really shouldn't use it.) So, your user class could be changed as follows:

class User {
   ...
   public function getDescriptor() {
   }
}

class UserDescriptor {
   ...
}

Best Answer

Related Solutions

Java – Constructor vs setter validations

Object-oriented – does this model-pattern have a name

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