CODEWITHSUNDEEP
javaarraysgenerics
Wiener Boat
Wiener Boat

Reputation: 446

Can't add to a generic array

Couldn't find elsewhere, so here goes: I'm trying to create a generic class that contains an array holding objects of the given type. I have the rest of the code somewhat working, but for some reason I can't call my add method with the type as a parameter. Here's the example:

public class Generic<E extends Item> {

    private E[] items = (E[])(new Object[5]);

    public void add(E neu) {
        this.items[0] = neu;
    }

    public void problematic(Class<E> clazz) {
        E neu = clazz.newInstance();
        this.items.add(neu);  // this line is the problem
    }

}

The given error is "Cannot invoke Add(E) on the array type E[]"

Upvotes: 0

Views: 770

Answers (2)

firephil
firephil

Reputation: 865

I guess instead of this.items.add(neu); use the method call add() this.add(neu);

But you are always adding to array[0] do you really want to do that ?

Also (E[])(new Object[5]); is an unsafe cast, as Jigar Joshi posted use an ArrayList instead A working example :

import java.util.ArrayList;

public class Generic <E extends Item> {

     private ArrayList<E> items = new ArrayList<E>();

        public void add(E neu) {
           this.items.add(neu);
        }

        public void problematic(E clazz) {

           this.add(clazz);  // this line is the problem
        }

}

class Item {}

The same with an Array of Object

public class Gen <E extends Item> {

  private Object[] items = new Object[5];
  private int itemCounter = 0;

    public void add(E neu) {

        if(itemCounter < items.length){
          this.items[itemCounter] = neu; 
          itemCounter +=1;
        }
    }

    public int length()
    {
        return itemCounter;
    }

   // testing the class
    public static void main(String[] args)
    {
        Item t0 = new Item();
        Item t1 = new Item();
        Item t2 = new Item();
        Item t3 = new Item();
        Item t4 = new Item();
        Item t5 = new Item();

        Gen<Item> g = new Gen<Item>();

        g.add(t0);
        g.add(t1);
        g.add(t2);
        g.add(t3);
        g.add(t4);
        g.add(t5); // ignored

        System.out.println(g.length());

    }
}

  class Item {}

Upvotes: 1

Jigar Joshi
Jigar Joshi

Reputation: 240898

array don't have add() method and so the compilation failure, change it to ArrayList since it looks like you don't know the initial size of your array

Upvotes: 2

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