Question

I have ‘builder’ class and Sonar gives the following warning:

Missing Static Method In Non Instantiatable Class
pmd : MissingStaticMethodInNonInstantiatableClass
A class that has private constructors and does not have any static methods or fields cannot be used

How would I refactor this class to satisfy the above check?
I’m scratching my head because I do use that class.

Sample use:

ViewBuilder vb = new ViewBuilder.Builder()
    .modelPart(CONTENT_PAGE, contentPageDao.get(id))
    .modelPart("navigation_sections", navigationSectionDao.list() )
    .modelPart("available_tags", tagDao.list() )
    .modelPart("available_albums", albumDao.list() )
    .section(CONTENT_PAGE)
    .page("index")
    .element("form")
    .action("/admin/content_page/save/" + id + ".html")
    .build();

Class itself:

import java.util.HashMap;
import java.util.Map;


 public final class ViewBuilder {

    private static final String ADMIN_LAYOUT = "admin/layout";
    private String layout = ADMIN_LAYOUT;
    private String section = "";

  private static Map<String, Object> viewParts = new HashMap<String, Object>();

  /**
   * @return the layout
   */ public String getLayout() {
    return layout;
  }

  /**
   * @param layout the layout to set
   */ public void setLayout(String layout) {
    this.layout = layout;
  }

  /**
   * @return the section
   */ public String getSection() {
    return section;
  }

  /**
   * @param section the section to set
   */ public void setSection(String section) {
    this.section = section;
  }

  public static class Builder{

    // required params
    private String layout;
    private String section;

    // optional params
    private Map<String, Object > viewParts = new HashMap<String, Object >();

    public Builder(){

        this.layout = ADMIN_LAYOUT;
        viewParts.put("layout", ADMIN_LAYOUT);

    }
    public Builder( String layout ){

      if( layout != null ){
        this.layout = layout;
        viewParts.put("layout", layout );
      } else {
        this.layout = ADMIN_LAYOUT;
        viewParts.put("layout", ADMIN_LAYOUT);
      }

    }// constructor
    public Builder modelPart( String val, Object o ){
      this.viewParts.put(val, o );
      return this;
    }

    public Builder action( String val ){
      this.viewParts.put("action", val);
      return this;
    }
    public Builder element( String val ){
      this.viewParts.put("element", val);
      return this;
    }
    public Builder section( String val ){
      this.section = val;
      this.viewParts.put("section", val);
      return this;
    }
    public Builder page( String val ){
      this.viewParts.put("page", val);
      return this;
    }
    public Builder layout( String val ){
      this.layout = val;
      return this;
    }

    public ViewBuilder build( ){
      return new ViewBuilder( this );
    }


  }// Builder

    private ViewBuilder(Builder builder){
      this.section = builder.section;
      this.layout = builder.layout;

      viewParts = builder.viewParts;
    }

  /**
   * Get the value of viewParts
   *
   * @return the value of viewParts
   */
  public Map<String, Object> getViewParts() { return viewParts; }

  /**
   * Set the value of viewParts
   *
   * @param viewParts new value of viewParts
   */
  public void setViewParts(Map<String, Object> viewParts) { this.viewParts = viewParts; }
}

Answer 1

Given that your nested Builder class is public and static, I really see little benefit in it being nested at all. I would recommend breaking it out into its own top level class. Of course, thats not why PMD is complaining. Your outer class, ViewBuilder, has no public constructors, and no static methods. As it exists right now, its a fairly useless ‘namespace wrapper’ around your Builder class. Either add a constructor to it, or get rid of it altogether.