Question

package portale.interfaccia;
public class PageIndex extends FlowPanel {
    protected Integer prova;

    private PageCenter center;
    public PageIndex() {
        this.center=new PageCenter();
        this.add(center);    
    }
}

package portale.interfaccia;
public class PageCenter extends FlowPanel {
    public PageCenter() {
        super.prova=2;
    }
}

why, if prova is protected, i can’t access to it by using super?
Cheers

Answer 1

PageCenter extends from FlowPanel, not from PageIndex. It looks like FlowPanel has no attribute named prova

If you want PageCenter to access a protected attribute from PageIndex using the super keyword, then you should extend from PageIndex.

public class PageCenter extends PageIndex{

   public PageCenter(){
      prova = 2;
   }
}

If you want both classes to extend from FlowPanel, try refactoring your code so that PageIndex and PageCenter know some utility class.

public class ProvaUtility{

    private Integer prova;

    public Integer getProva(){}

    public void setProva(Integer p){}
}

Then you could use it like this:

public class PageIndex extends FlowPanel{

    private ProvaUtility utility;

    private PageCenter center;

    public PageIndex(ProvaUtility pu){

        this.utility = pu;
        this.center = new PageCenter(pu);
        this.add(this.center);
    } 

    public Integer getProva(){
         return this.utility.getProva();
     }
}

 public class PageCenter extends FlowPanel{

    private ProvaUtility utility;

    public PageCenter(ProvaUtility u){
       this.utility = u;
       this.utility.setProva(2);
    }
 }

If passing this reference around doesn’t make it for you, try using a Singleton

class ProvaSingleton{

   private static ProvaSingleton instance = null;

   private Integer prova;

   private ProvaSingleton(){
      prova = 2;
   }

   public static ProvaSingleton getInstance(){

      if (instance == null){
          instance = new ProvaSingleton();
      }
      return instance;
   }

   public Integer getProva(){ return this.prova;}

   public void setProva(Integer p){this.prova = p;}
}

Then call it by:

ProvaInstance.getInstance().getProva()