RFR: 8329760: Add indexOf(Predicate<? super E> filter) to java.util.List interface [v11]

[Evemose]

On Fri, 19 Apr 2024 15:49:11 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 one additional commit since the last revision:
> 
>   reverted code style changes in Vector

> > > I noticed that most (if not all) methods don't ensure non-nullability of `filter` so NPE would only be thrown if the list is not empty.
> > 
> > 
> > Yeah, thats true. not sure if it has to throw NPE even if list is emply
> 
> Yes, it does. If it shouldn't, then why isn't code in the java.util.List is like this:
> 
> ```java
> default int findIndex(Predicate<? super T> filter) {
> 	ListIterator<T> iterator = listIterator();
> 	if (!iterator.hasNext()) return -1;
> 	Objects.requireNonNull(filter);
> 	int index = 0;
> 	do {
> 		if (filter.test(iterator.next()))
> 			return index;
> 		index++;
> 	} while (iterator.hasNext());
> 	return -1;
> }
> ```
> 
> Also see methods like `removveIf`. All methods should do checks even if they essentially do nothing.

ok, i will fix this in a while

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

PR Comment: https://git.openjdk.org/jdk/pull/18639#issuecomment-2067357432