RFR: 8329760: Add indexOf(Predicate<? super E> filter) to java.util.List interface [v12]

[Chen Liang]

On Tue, 23 Apr 2024 13:51:54 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 bas...
>
> Evemose has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - Added Objects import to sun List
>  - Replaced on-demand import in com.sun....List
>  - added non-null assertions

src/java.base/share/classes/java/util/LinkedList.java line 1507:

> 1505: 
> 1506:         public int findLastIndex(Predicate<? super E> filter) {
> 1507:             return rlist.findLastIndex(filter);

Hmm, this view is supposed to be reversed... so last and first need a swap. This is a bug in the current codebase, a good bug to fix indeed.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/18639#discussion_r1573456708