use abstract class inputverifier java in another class

Question

I have two classes

public class Finestra extends javax.swing.JFrame{
    ........
    jtextField.setinputVerifier(.....):
}

public abstract class Verifica extends InputVerifier{
    String message;
    public Verifica(String message){
    }

    public abstract boolean verifica(JtextField c);

    public boolean verify(Jcomponent c){
         JTextField c = (JTextField) jc;
    if (esito(c) == false){
        return false;
    }else{
        return true;
    }
}
    }
}

I want to use Verifca class in finestra. I don't extends it because there is javax.swing.JFrame. Can i do to use Verifica? and is it a problem the only abstract method verifica.

I try this, but doesn' work

      testo.setInputVerifier(new Verifica("error") {
         public boolean verifica(testo){
             if (testo.getText == null){
                return true;
             }else{
                  return false;
             }

           }

      });

Answer 1

What you're trying to do is to have an abstract class Verifica and then, when using it, to create an anonymous class with a custom implementation of the method verifica.

In the anonymous class definition that you're doing, you must override the variable with the same signature like this for example:

testo.setInputVerifier(new Verifica("error") {
     @Override
     public boolean verifica(JTextField c) {
         if (testo.getText == null){
            return true;
         } else{
              return false;
         }
     }

  });

You cannot "bind" your variable testo as the parameter for your verifica method in the anonymous class. You can, however, refer to testo directly from the outside scope of you anonymous class (so it gets bound in the implementation, not the signature of the method), resulting in something like this:

public abstract class Verifica extends InputVerifier {
    public abstract boolean verifica();
}

and

testo.setInputVerifier(new Verifica("error") {
     public boolean verifica() {
         if (testo.getText == null) {
            return true;
         } else {
              return false;
         }
       }
  });