如何将@Override toString与接口对象的ArrayList一起使用？

Question

My understanding of interfaces is that they cannot contain method definitions, only signatures and constant declarations. I have an arraylist that contains a collection of interface objects. In this case, it looks like:

List< StoreItem > items = new ArrayList< StoreItem >();

and StoreItem is my interface that looks like this:

public interface StoreItem {
//Operations
public String getMaker();
public Patron getItemBuyer();
public Date getManufactureDate();
public String getManufacturer();
public String getProductName();
public void setItemBuyer(Patron purchase);
    }

I have a method to create a new item and add it to the list. It seems to work ok, in that I'm not getting any problems on the unit test and no exceptions are caught. However I have that classic newbie problem where I want to print the arraylist to see the contents with my own eyes, and I understand I need to override the toString method for StoreItem. But StoreItem is an interface and obviously it won't let me do anything like this within the Interface. I also have an abstract class implementing this interface, and three subclasses of that abstract class. I am creating an object of one of these subclasses as the StoreItem, so I tried to do a toString override within this subclass. I can't get this to work. I tried:

public String toString(){
    return super.productName();
}

Which it didn't like, because within the abstract super class productName is private, and needs to be for the sake of the project. I decided to go ahead and change productName to protected anyway just to see if it would still work. I still just get the memory location (something like @d9sdf83j) when printing the list. So I set it back to private and tried to have the toString use the getter method from the superclass on the return, so:

public String toString(){
    return super.getProductName();
}

I still just get the memory location. I don't know if this is enough code to portray what's going on and what I'm trying to do. I'm hoping the error is rudimentary enough that someone wiser than me can just spot it and point it out, but I can add more code if necessary. Thanks in advance.

I still can't get it to work. I'm going to add the actual classes and see if that helps.

public abstract class AbstractStoreItem implements StoreItem{

//attributes
private String product;
private Date manufactureDate;
private String manufacturer;
private String distibutor;
private Patron buyer;

//operations
public AbstractStoreItem(String product, String manufacturer, String distibutor, Date manufactureDate) {
    this.product = product;
    this.manufactureDate = manufactureDate;
    this.manufacturer = manufacturer;
    this.distibutor = distibutor;
}

@Override
public String toString() {
    return this.product;

}

@Override
public String getManufacturer() {
    // TODO Auto-generated method stub
    return manufacturer;
}

@Override
public Patron getBuyer() {
    // TODO Auto-generated method stub
    return buyer;
}

@Override
public Date getManufactureDate() {
    // TODO Auto-generated method stub
    return manufacturerDate;
}

@Override
public String getDistributor() {
    // TODO Auto-generated method stub
    return distributor;
}

@Override
public String getProduct() {
    // TODO Auto-generated method stub
    return product;
}

@Override
public void setBuyer(Patron buyer) {
    this.buyer= buyer;

}

}

Here is the subclass of the abstract class. This is the object I'm adding to the list:

public class Widget extends AbstractStoreItem{

//attributes
private Type type;
private int unitQuantity;

//operations
public Widget(String product, String manufacturer, String distributor, Date manufactureDate, Type gearType, int unitQuantity){
    super(product, manufacturer, distributor, manufactureDate);

    this.type = gearType;
    this.unitQuantity = unitQuantity;
}

public Type getType(){
    return type;
}

public int getUnitQuantity(){
    return unitQuantity;
}

@Override
public void setBuyer(Patron Buyer) {
    // TODO Auto-generated method stub

}

@Override
public String toString() {
    return super.getManufacturer();
}

}

Not sure what to do to the toString method.

Answer 1

You need to override toString in the class which implements StoreItem of which instances you are adding to List

interface StoreItem {
    String name();
}

static class Pen implements StoreItem {

    @Override
    public String name() {
        return Pen.class.getName();
    }

    @Override
    public String toString() {
        return "Pen to String";
    }

}

public static void main(String[] args) {
    List<StoreItem> items= new ArrayList<StoreItem>();
    items.add(new Pen());
    System.out.println(items);
}

Will Print

 [Pen to String]