Java toggled list

Question

I need to have a list that has an "enabled" filter such as:

[
{
    "enabled": false,
    "value": {
        "number": 0
    }
},
{
    "enabled": true,
    "value": {
        "number": 1
    }
},
{
    "enabled": false,
    "value": {
        "number": 2
    }
},
{
    "enabled": true,
    "value": {
        "number": 3
    }
}
]

If i were to iterate over this list printing each "number" using either Iterable.iterator() or a standard for loop with get(i) it'd output this:

1, 3

and it's size() would return 2. But if i go ahead and enable the first element it would print instead:

0, 1, 3

and it's size() would return 3.

Is there a standard implementation of something like this?

The list would feature operations to work on the unfiltered version of it, so as to be able to actually toggle each element.

I used JSON to simplify the representation of the contents of my hypothetical list in order to be able to exemplify the behaviour i want from it. — Machinarius, Jul 05 '13 at 17:08
To answer your question of a "standard way"? No. But there's any number of ways to approach the problem. — Brian Roach, Jul 05 '13 at 17:09
I'm asking this mostly out of curiosity and to see if someone had already tackled the problem at hand, not that i can't build it myself. — Machinarius, Jul 05 '13 at 17:13
i believe a custom linked list implementation would be better in this case. — ajay.patel, Jul 05 '13 at 17:16

score 1 · Answer 1 · answered Jul 05 '13 at 17:47

I think the easiest way is going to be a custom collection that simply skips over elements to the next enabled element

public interface Enabled
{
    public boolean isEnabled();
}

public class EnabledCollection<T extends Enabled> implements List<T>
{
    private List<T> list = new ArrayList<T>();

    @Override
    public Iterator<T> iterator() {        
        Iterator<T> it = new Iterator<T>() {

            private int i = 0;

            @Override
            public boolean hasNext() {
                return i < list.size();
            }

            @Override
            public T next() {
                T o = list.get(++i);

                while (!o.isEnabled() && hasNext()) { o = list.get(++i); }

                return o;
            }

            @Override
            public void remove() {
                // todo
            }
        };

        return it;
    }

    @Override
    public T get(int i)
    {
        T o = list.get(i);

        while (!o.isEnabled() && i < list.size()) { o = list.get(++i); }

        return o;
    }

    // etc
}

score 0 · Answer 2 · edited May 23 '17 at 12:05

0

I think you have to override some standard object to get this results.

Example for List override: Problem overriding ArrayList add method

edited May 23 '17 at 12:05

Community

1
1

answered Jul 05 '13 at 17:11

surfealokesea

4,971
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That inmediately came to my mind, but i am asking if there was something already made. – Machinarius Jul 05 '13 at 17:14
You should mention before you already now this solution. If there is some standard object to do this, I don't now. – surfealokesea Jul 05 '13 at 17:15

Java toggled list

2 Answers2