如何将参数传递给二级超类

Question

I am trying to understand inheritence and have some problems to understand.

public class SiteTemplate extends SiteTemplateMethods

    public SiteTemplate(String country, String language, HttpServletRequest request){
        super();


    }   

public class SiteTemplateMethods extends Resources

public class Resources extends PropertyFiles

1) class PropertyFiles all methods will be accessible from classes Resources , SiteTemplateMethods and SiteTemplate . Is that right?

2) super(); in SiteTemplate constructor will pass all parameters to SiteTemplateMethods but these parameters are not required here in class SiteTemplateMethods how can I get the parameters of the SiteTemplate class to second level super class Resource class?

Best regards

Answer 1

1) class PropertyFiles all methods will be accessible from classes Resources , SiteTemplateMethods and SiteTemplate . Is that right?

No, it is not right. All public and protected members of PropertyFiles will be accessible to descendant classes, including Resources , SiteTemplateMethods , and SiteTemplate , but the private methods of PropertyFiles will not be accessible to subclasses. Package-private methods will be accessible to descendant classes only if they are in the same package as Resources . See https://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html .

There are additional limitations on accessing methods that have been overridden (as first noted by @Gergely).

2) super(); in SiteTemplate constructor will pass all parameters to SiteTemplateMethods

No, it won't. super() with no arguments invokes the no-argument constructor of the immediate superclass, passing no arguments to it. If the immediate superclass does not have an accessible no-arg constructor then the invocation is invalid.

To invoke a different constructor, ie as one that accepts arguments, you must invoke super() with a corresponding argument list.

but these parameters are not required here in class SiteTemplateMethods how can I get the parameters of the SiteTemplate class to second level super class Resource class?

If SiteTemplateMethods has an accessible constructor that will pass the arguments on to an accessible (to it) constructor of Resource , then you can use a corresponding super() invocation (with arguments) at the beginning of SiteTemplate 's constructor. Otherwise, SiteTemplate 's constructor will need to apply the parameters directly, in a manner appropriate to class Resource , such as by invoking property setter methods.

Answer 2

Let's declare some methods.

public class Resources extends PropertyFiles{
     public Resources(String country,String language){
          super();
          //...
     }
     public void a(){
          //...
     }
     public void b(){
          //...
     }
     public void c(){
          //...
     }
}
public class SiteTemplateMethods extends Resources{
     public SiteTemplateMethods(){
          super("foo","bar");
          //...
     }
     public void a(){
          //...
     }
     public void b(){
          super.b();//This will call the superclass's method
          //...
     }
}

1) In SiteTemplate , you can access c() from Resources but not a() and b() , because they were overridden by SiteTemplateMethods . Calling a() will call the a() method in SiteTemplateMethods instead. If you have an instance of SiteTemplate then you can't call the a() method of Resources . The b() method in SiteTemplateMethods however, calls the superclass method, and executes additional code after it.

2) In constructor calls you can only access constructors declared by the class that your class directly extends. In the given example You can't call super(String country,String language) in SiteTemplate , unless SiteTemplateMethods declares the following:

public SiteTemplateMethods(String country,String language){
     super(country,language);
     //...
}

Also note that methods with different parameters are treated as two different methods. so a(String str) does not override a() . However, this is not true, if the overriding method is fully applicable for the arguments of the previous method. So a(Object o) does override a(String str) .