Ndtyjky

I have been given the following main method and must write the code for the ObjectList class. I am supposed to infer the necessary functions of the ObjectList class and write the class myself, however I am unsure exactly what I need to do to fulfill this function. Any help understanding this is greatly appreciated. This is the code I was given:

   ObjectList ol = new ObjectList(3);



   String s = "Im Happy";

   Dog d = new Dog();

   DVD v = new DVD();

   Integer i = 1234;



   System.out.println(ol.add(s));

   System.out.println(ol.add(d));

   System.out.println(ol.add(v));

   System.out.println(ol.add(i));



   ol.remove(0);

   System.out.println(ol.add(i));





   System.out.println("Is the list full? "+ isFull()); 

   System.out.println("Is the list empty? "+ isEmpty());



   System.out.println("Total number of objects in the list: " + getTotal());



   Object g = ol.getObject(1);

   g.bark();

It's quite simple just need to create a list of Object types using ArrayList or LinkedList in the ObjectList class and implement the function as follows

public class ObjectList{

private ArrayList<Object> objects;

public ObjectList(int size)

{

    objects = new ArrayList<Object>(size);

}



public String add (Object object)

{

    objects.add(object);

    //anything you would like to return I'm just returning a string

    return "Object Added";

}



public void remove (int index)

{

    objects.remove(index);

}



public boolean isEmpty()

{

    return objects.isEmpty();

}



public int getTotal()

{

    return objects.size();

}



public Object getObject(int index)

{

    return objects.get(index);

}

}

The isFull()is not needed since ArrayListsize can change dynamically. You can use a simple array instead of ArrayList and then implement the isFull() function.

Also when getting an object using the get getObject() function, you need to cast it to the correct type before using there function. In your code g.bark() won't work because Object doesn't have a bark function

Object g = ol.getObject(1);



//This can give a runtime error if g is not a Dog

//Use try catch when casting

Dog d = (Dog)g;



d.bark();

EDIT

This is how you would implement isFull() and other functions if using arrays instead of ArrayList but for the sake of simplicity use the ArrayList version

 public class ObjectList{

 private Object objects;

 private int size = 0;

 private int currentIndex = 0;





public ObjectList(int size)

{

    this.size = size;

    objects = new Object[size];

}



 private boolean isFull() {

    if(currentIndex == size)

        return true;

    else

        return false;

 }



 public String add (java.lang.Object object)

{

    if ( ! isFull() ) {

        objects[currentIndex] = object;

        currentIndex++;

        return "Object added";

    }

    return "List full : object not added";



}



public void remove (int index)

{

    if( !isEmpty() ) {

        //shifting all the object to the left of deleted object 1 index to the left to fill the empty space

        for (int i = index; i < size - 1; i++) {

            objects[i] = objects[i + 1];

        }

        currentIndex--;

    }

}



public boolean isEmpty()

{

    if(currentIndex == 0)

        return true;

    else

        return false;

}



public int getTotal()

{

    return currentIndex;

}



public java.lang.Object getObject(int index)

{

    if(index < currentIndex)

     return objects[index];

    else

        return  null;

}

}

What it seems you want to achieve is "expand" the functionality of an ArrayList and create a custom list of objects. What you could do is to create a class extending the ArrayList and define/override any other methods you want.

public class ObjectList extends ArrayList<Object> {

//constructor with initial capacity

private int length;

public ObjectList(int size){

   super(size);

   this.length= size;

}



public Object getObject(int index){

    return this.get(index);

}

}

Now you have the add and remove functions inherited from the ArrayList class and the getObject method.

Concerning the isFull method, you can check if the size of your ObjectList class is equal to the size it was instantiated with

if(this.size() == this.length){

return true

}

return false;

And getTotal

public int getTotal(){

return this.size();

}