RFR: 8329760: Add indexOf(Predicate<? super E> filter) to java..util.List interface

[xxDark]

On Fri, 5 Apr 2024 00:00:58 GMT, Evemose <duke at openjdk.org> wrote:

> **Subject**
> Addition of Predicate-based `indexOf` and `lastIndexOf` methods to `java.util.List`
> 
> **Motivation**
> The motivation behind this proposal is to enhance the functionality of the `List` interface by providing a more flexible way to find the index of an element. Currently, the `indexOf` and `lastIndexOf` methods only accept an object as a parameter. This limits the flexibility of these methods as they can only find the index of exact object matches.
> 
> The proposed methods would accept a `Predicate` as a parameter, allowing users to define a condition that the desired element must meet. This would provide a more flexible and powerful way to find the index of an element in a list.
> 
> Here is a brief overview of the changes made in this pull request:
> 
> 1. Added the `indexOf(Predicate<? super E> filter)` method to the `List` interface.
> 2. Added the `lastIndexOf(Predicate<? super E> filter)` method to the `List` interface.
> 3. Implemented these methods in all non-abstract classes that implement the `List` interface.
> 
> The changes have been thoroughly tested to ensure they work as expected and do not introduce any regressions. The test cases cover a variety of scenarios to ensure the robustness of the implementation.
> 
> For example, consider the following test case:
> 
> List<String> list = new ArrayList<>();
> list.add("Object one");
> list.add("NotObject two");
> list.add("NotObject three");
> 
> int index1 = list.indexOf(s -> s.contains("ct t"));
> System.out.println(index1); // Expected output: 1
> int index2 = list.lastIndexOf(s -> s.startsWith("NotObject"));
> System.out.println(index2); // Expected output: 2
> 
> 
> Currently, to achieve the same result, we would have to use a more verbose approach:
> 
> int index1 = IntStream.range(0, list.size())
>                      .filter(i -> list.get(i).contains("ct t"))
>                      .findFirst()
>                      .orElse(-1);
> System.out.println(index1); // Output: 1
> int index2 = IntStream.range(0, list.size())
>                          .filter(i -> list.get(i).startsWith("NotObject"))
>                          .reduce((first, second) -> second)
>                          .orElse(-1);
> System.out.println(index2); // Output: 2
> 
> 
> I believe these additions would greatly enhance the functionality and flexibility of the `List` interface, making it more powerful and user-friendly. I look forward to your feedback and am open to making any necessary changes based on your suggestions.
> 
> Thank you for considering this proposal.
> 
> Best regards

Won't this make some calls ambiguous?
For example, passing `null`:

List<String> l;
l.indexOf(""); // Fine
l.indexOf(null); // Now fails to compile

Edit: I'm not a reviewer, but I decided to point this out.

src/java.base/share/classes/java/util/LinkedList.java line 1519:

> 1517: 
> 1518:         public int findIndex(Predicate<? super E> filter) {
> 1519:             return rlist.indexOf(filter);

Should be `findIndex`? Similarly with `findLastIndex`.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/18639#issuecomment-2045324794
PR Review Comment: https://git.openjdk.org/jdk/pull/18639#discussion_r1559268478