Internal interfaces?

Question

I am new to Java and I don’t understand what this structure is. I know what an interface is and how it is defined, but in this case I really don't know. Could you talk about what?

public interface WebConstants { public interface Framework { String ACTION = "action"; } public interface Look { String LIST_CONT = "list.cont"; } } 

Answer 1

Each field inside the interface is implicitly open, static, and final. In this case, WebConstants declares an internal interface (open, static and final) Framework and (public, static and final) Look , which also have some (public, static and final) string fields.

This is a (not very general) way of ordering constants in your code, with this structure you can enter:

 String action = WebConstants.Framework.ACTION; String list = WebConstants.Look.LIST_CONT; 

The advantage of this is that since WebConstants is an interface, you cannot accidentally initiate it

Answer 2

You might want to look through the listings if you use a similar solution:

 public enum WebConstants { ACTION("action"), LIST_COUNT("list.count"); private String display; private WebConstants(String display) { this.display = display; } public String getDisplay() { return display; } } 

So you can use it by calling WebConstants.ACTION.getDisplay ().

Having a constant interface doesn't really make any sense to me. The best way to do things might be to have abstract access methods.

 public interface ActionAware { public String getAction(); } public interface ListCountAware { public String getListCount(); } public abstract class AbstractUseCase implements ActionAware, ListCountAware { public void doSomething() { String action = getAction(); String listCount = getListCount(); } } public final class SpecificUseCase extends AbstractUseCase { public final static String ACTION = "specific.action"; public final static String LIST_COUNT = "specific.list.count"; public String getListCount() { return LIST_COUNT; } public String getAction() { return ACTION; } // other methods }