Java ArrayList addAll only adding 1 element?

Question

So I basically put some Integer objects in an ArrayList x, then put some in an ArrayList y, then did y.addAll(x), but it seems to be only adding the first one and leaving out all the rest! Isn't it supposed to add ALL? I looked it up on Oracle and they showed what seemed to be the EXACT SAME EXAMPLE yet mine is not working properly. Here is my code:

ArrayList<Integer> x = new ArrayList<Integer>();
Integer a = 1;
Integer b = 2;
Integer c = 3;
x.add(a);
x.add(b);
ArrayList< Integer> y = new ArrayList< Integer>();
y.addAll(x);

yet y seems to only have 1 in it and missing the 2 and the 3.

What am I doing wrong?

EDIT: Yes, sorry, I know I didn't actually add c to x yet, but even when I do, and then print y, I still get [1] instead of [1,2,3]. This is what I don't understand.

import java.util.ArrayList;
public class SumArrayList {

    public static void main(String[] args) {

        ArrayList<Integer> x = new ArrayList<Integer>();
        Integer a = 1;
        Integer b = 2;
        Integer c = 3;
        x.add(a);
        x.add(b);
        System.out.println(x);
        //System.out.println(calculateSumArrayListHelper(x));

        ArrayList<Integer> y = new ArrayList<Integer>();
        y.addAll(x);
        System.out.println(y);
        //System.out.println(calculateSumArrayListHelper(y));
    }
}

Here is a pic of what I see: http://postimg.org/image/ms0y68nnh/

I'm sure you get [1,2] not just 3 because you haven't added it — airudah
– airudah, Commented Apr 13, 2016 at 8:25
Okay, here I'll just give you my entire code, and yeah I realize I didn't add 3, but it's still printing just [1] when I print y and [1,2] when i print x — Azmera
– Azmera, Commented Apr 13, 2016 at 8:28

André Stannek · Accepted Answer · 2016-04-13 08:45:58Z

2

With the picture you have posted it is clear. You are calling calculateSumArrayListHelper(x) before the addAll(). Inside that method you remove elements from the given list. So at the time you call y.addAll(x), elements have been removed from x.

answered Apr 13, 2016 at 8:45

André Stannek

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1 Comment

Azmera Over a year ago

Oh my goodddddddd............................ I'm such a idiot. Thank you so much

Guillaume Barré · Accepted Answer · 2016-04-13 08:46:52Z

2

In your code after executing y.addAll(x); y will contain only 2 elements [1,2]. you never add c to x:

ArrayList<Integer> x = new ArrayList<>();
Integer a = 1;
Integer b = 2;
Integer c = 3;
x.add(a);
x.add(b);
x.add(c); // add c to x
ArrayList< Integer> y = new ArrayList<>();
y.addAll(x);
System.out.println("size = " + y.size());

Will produce :

size = 3

And y will contain :

[1,2,3]

You are removing item from x in your method calculateSumArrayListHelper(). That's why you don't have the expected result.

Comment all calls to this method and check the content of y... It should be right.

edited Apr 13, 2016 at 8:46

answered Apr 13, 2016 at 8:27

Guillaume Barré

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3 Comments

Azmera Over a year ago

Yeah this is what I don't understand. I literally have done this exactly, but when I print y, it just gives me "[1]" and not "[1,2,3]"

Guillaume Barré Over a year ago

And printing y.size() what is the result?

Azmera Over a year ago

when I print y.size() it says 1

Deepesh kumar Gupta · Accepted Answer · 2016-04-13 08:34:15Z

0

Just put sop on last line.

System.out.println(y);

So that you can see the result.which is coming [1, 2] in my system. You are not getting 3 as because you never add it in X.

x.add(a);
x.add(b);
x.add(c);

answered Apr 13, 2016 at 8:34

Deepesh kumar Gupta

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