I need to write a java method to get specific information from an object. However, the object can either be of type A or of type B. Here is the part of my code :

class Composant{

int quantité;
static Composee pieceCompo;
static Simple pieceSimp;

public Composant(Composee piece, int nombre){
    pieceCompo = piece;
    quantité = nombre;
}

public Composant(Simple piece, int nombre){
    pieceSimp = piece;
    quantité = nombre;
}
public Composee getPiece(){
    return pieceCompo;
}
public Simple getPiece(){
    return pieceSimp;
}
public int getQuantite(){
    return quantité;
}}

When I write it like that it raises an error saying "Duplicate method". How can I get this to work?

CodePudding user response：

As per JLS, §8.4.2:

...

The signature of a method m1 is a subsignature of the signature of a method m2 if either:

• m2 has the same signature as m1, or
• the signature of m1 is the same as the erasure (§4.6) of the signature of m2.

Two method signatures m1 and m2 are override-equivalent iff either m1 is a subsignature of m2 or m2 is a subsignature of m1.

It is a compile-time error to declare two methods with override-equivalent signatures in a class.

...

This means that methods public Composee getPiece() and Simple getPiece() are override-equivalent. Since those two methods are in the same class, the compiler generates a compile-time error.

As was pointed out by azro in the comments, we can instead write two separate getters Composee getComposee() and Simple getSimple().

If Simple and Composee have a common supertype (e.g. Piece), we can return write a Piece getPiece() instead.

CodePudding user response：

Try this maybe:

public class Composant<T>{
    private final int quantite;
    private final T comp;

    public Composant(T comp,int quantite) throws BadTypeException {
        if(!(comp instanceof Composee) || !(comp instanceof Simple)) throw new BadTypeException("Can't create Composant with \""   comp.getClass().getName()   "\" type object!");
        this.comp = comp;
        this.quantite = quantite;
    }

    public T getPiece(){
        return this.comp;
    }

    public int getQuantite(){
        return this.quantite;
    }
}

Exception is:

//  If you don't want to catch exception, change it to "RuntimeException"
class BadTypeException extends Exception{
    public BadTypeException(String message){
        super(message);
    }
}

And create like this:

    try {
        new Composant<Composee>(new Composee(),4);
    } catch (BadTypeException e) {
        e.printStackTrace();
    }