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From "Jonas Holtkamp (JIRA)" <>
Subject [jira] [Commented] (COLLECTIONS-604) More uniform safe-null methods in CollectionUtils
Date Sun, 28 May 2017 14:01:04 GMT


Jonas Holtkamp commented on COLLECTIONS-604:

A good comparison for {{null}}-behaviour would be a look to {{StringUtils}} et. al. in my
mind, because 
a) {{StringUtils}} handles {{null}} values reasonably and
b) that would align behaviours across the different Commons libraries

> More uniform safe-null methods in CollectionUtils
> -------------------------------------------------
>                 Key: COLLECTIONS-604
>                 URL:
>             Project: Commons Collections
>          Issue Type: Bug
>          Components: Collection
>    Affects Versions: 4.1
>            Reporter: Bruno P. Kinoshita
>            Assignee: Bruno P. Kinoshita
>            Priority: Minor
>         Attachments: COLLECTIONS-604.csv
> Currently, there are 65 public methods in `CollectionUtils`. And 53 without the deprecated
ones. Out of these, 24 handle `null` arguments. The remaining methods throw a `NullPointerException`
(NPE) at some part of its code.
> The methods that handle nulls, throw NPE, or return empty columns, boolean values, or
just doesn't do anything.
> As a user of the API, I would expect a more uniform behaviour across the methods of `CollectionUtils`.
COLLECTIONS-600 address one of these methods.
> `removeAll` (2x) and `retainAll` (2x) both state that a NPE will be thrown if either
parameter is `null`. However, they never check if the values are null, and instead allow the
code to run until a NPE is thrown.
> And the following code shows that `isEmpty` and `isFull` behave differently too.
> {code:java}
> Collection<String> c = null;
> System.out.println(CollectionUtils.isEmpty(c)); // return true
> System.out.println(CollectionUtils.isFull(c));  // throws a NPE
> {code}
> If I don't have to worry about `null`s with `#isEmpty`, I would expect the same from
its related-method `#isFull`.
> What would be a good approach for it? Define a behaviour to all methods? Or leave as
is, but add more documentation?
> There are a few methods that can easily be updated to check for `null` values. Others
would require a bit more thinking. An example if the method in question for COLLECTIONS-600.
It checks equality of collections, and when both collections are `null`, it says that they
are equals. Google Guava [Iterables#elementsEqual|]
and [Iterators#elementsEqual|]
do not check for null values, for what it is worth.

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