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

[Chen Liang]

On Fri, 5 Apr 2024 00:31:22 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...
>
> side note: looks like this code have been reformated and some unused imports has been reformated. jdk compiles and works just fine, so i guess its not a big deal

Hello @Evemose, if we add an API we should also consider if implementation can efficiently implement it. How is this new API better than using a ListIterator directly so it's worth the additional methods?

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PR Comment: https://git.openjdk.org/jdk/pull/18639#issuecomment-2039920614