I am working on a project that uses abstract classes. I have mad the class Item, and then I made a "Snickers" and a "Mars" class that both extend the Item class.

I am using it in stacks, and after I fill these stacks, I am trying to print out the name of the top, in this case, Snickers. I tried calling the getName() method directly, but it tells me that it is undeclared. When I try to use it using the super keyword like System.out.println(snickersStack.top().super().getName()) there is an error that says "void cannot be derefferenced", which I can't really understand because the method I am trying to use, is a method that returns a String.

This is the Item class:

public abstract class Item {
    private float preis;
    private String name;
    private boolean haltbar;
    
    public Item(float pPreis, String pName, boolean pHaltbar)
    {
        preis = pPreis;
        name = pName;
        haltbar = pHaltbar;
    }
    
    public float getPreis() {
        return preis;
    }
    
    public String getName() {
        return name;
    }
    
    public boolean getHaltbar() {
        return haltbar;
    }
    
    public void setPreis(float pPreis) {
        preis = pPreis;
    }
    
    public void setName(String pName) {
        name = pName;
    }
    
    public void setHaltbar(boolean pHaltbar) {
        haltbar = pHaltbar;
    }
}

which clearly has the getName() method, this is the Snickers method, which just refferences the Item class:

public class Snickers extends Item {
    public Snickers(boolean pHaltbar) { 
        super(1.2f, "Snickers", pHaltbar);
    }
}

and this is the way I fill different amounts of Items into the stack, at the bottom there is the line with my problem.

public void fuelleStacks() {
    //random int 0 - 7
    randomInt = random.nextInt(8);
    
    //fuelle snickersStack
    while(randomInt != 0) {
        randomBool = random.nextBoolean();
        Snickers snickers = new Snickers(randomBool);
        
        snickersStack.push(snickers);
        randomInt--;
    }
    
    //fuelle marsStack
    randomInt = random.nextInt(8);
    while(randomInt != 0) {
        randomBool = random.nextBoolean();
        Mars mars = new Mars(randomBool);
        
        marsStack.push(mars);
        randomInt--;
    }
    System.out.println(snickersStack.top().super().getName());
}

I have declared and initialized the stack itself in the same class, like so:

public class Automat {
    public Stack snickersStack;
    
    public Automat() {
        snickersStack = new Stack<Snickers>();
        marsStack = new Stack<Mars>();
    }
}

I did not import a Stack class, instead I have another class called Stack that contains this code (that's why I used top(), not peek() like you do with the normal Stack class):

public class Stack<ContentType> {

  private class StackNode {

    private ContentType content = null;
    private StackNode nextNode = null;

    public StackNode(ContentType pContent) {
      content = pContent;
      nextNode = null;
    }

    public void setNext(StackNode pNext) {
      nextNode = pNext;
    }

    public StackNode getNext() {
      return nextNode;
    }

    /**
     * @return das Inhaltsobjekt vom Typ ContentType
     */
    public ContentType getContent() {
      return content;
    }
  }

  private StackNode head;
  private int anzahl;

  public Stack() {
    head = null;
    anzahl = 0;
  }

  public boolean isEmpty() {
    return (head == null);
  }

  public void push(ContentType pContent) {
    if (pContent != null) {
      StackNode node = new StackNode(pContent);
      node.setNext(head);
      head = node;
      anzahl  ;
    }
  }

  public void pop() {
    if (!isEmpty()) {
      head = head.getNext();
      anzahl--;
    }
  }
  
  public ContentType top() {
    if (!this.isEmpty()) {
      return head.getContent();
    } else {
      return null;
    }
  }
  
  public int getAnzahl() {
      return anzahl;
    }
}

CodePudding user response：

The code snickersStack.top().super().getName() has two things wrong. You need to use peek() to look at the top element of the stack. And super() is not a thing either. If you want to "reach" the getName() method you can do so by just using it on the object you get from peek(). The method is inherited from the base class.

CodePudding user response：

snickersStack.top().super().getName() is an incorrect use of the keyword super(). super() can only be called as the first line in a constructor. In fact, you use it correctly here:

public class Snickers extends Item {
    public Snickers(boolean pHaltbar) { 
        super(1.2f, "Snickers", pHaltbar);
    }
}

For more details, check out this documentation about super.

CodePudding user response：

You declared snickersStack as raw type:

public class Automat {
    public Stack snickersStack;
}

That means for the java compiler that it can contain any kind of object. And since Object doesn't have a getName() method you cannot call getName() on the result of snickersStack.top().

To fix this you must declare the snickersStack as a Stack<Snickers>:

public class Automat {
    public Stack<Snickers> snickersStack;
}