On Fri, 5 Apr 2024 00:00:58 GMT, Evemose <d...@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
Newly added methods to existing widely‑implemented non‑sealed and non‑preview
interfaces in `java.base` must be `default` to avoid source incompatibilities
and runtime errors, so move the implementations from `AbstractList` to `List`:
I’m in favour of using `findIndex`, which also avoids the issue with
`List<Predicate<…>>::indexOf` being ambiguous and having binary incompatible
bridge methods.
src/java.base/share/classes/java/util/AbstractList.java line 29:
> 27:
> 28: import java.util.function.Consumer;
> 29: import java.util.function.Predicate;
This is now unused:
Suggestion:
src/java.base/share/classes/java/util/AbstractList.java line 221:
> 219: return -1;
> 220: }
> 221:
Suggestion:
src/java.base/share/classes/java/util/AbstractList.java line 269:
> 267: return -1;
> 268: }
> 269:
Suggestion:
src/java.base/share/classes/java/util/List.java line 702:
> 700: * (<a
> href="Collection.html#optional-restrictions">optional</a>)
> 701: */
> 702: int lastIndexOf(Predicate<? super E> filter);
Suggestion:
/**
* Returns the index of the first occurrence of matching element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the lowest index {@code i} such that
* {@code filter.test(get(i))},
* or -1 if there is no such index.
*
* @implSpec
* This implementation first gets a list iterator (with
* {@code listIterator()}). Then, it iterates over the list until a
* matching element is found or the beginning of the list is reached.
*
* @param filter a predicate to search for
* @return the index of the first occurrence of the specified element in
* this list, or -1 if this list does not contain the element
* @throws NullPointerException if passed filter is null
*/
default int indexOf(Predicate<? super E> filter) {
Objects.requireNonNull(filter);
ListIterator<E> it = listIterator();
while (it.hasNext()) {
E e = it.next();
if (filter.test(e)) {
return it.previousIndex();
}
}
return -1;
}
/**
* Returns the index of the last occurrence of matching element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the highest index {@code i} such that
* {@code Objects.equals(o, get(i))},
* or -1 if there is no such index.
*
* @implSpec
* This implementation first gets a list iterator that points to the end
* of the list (with {@code listIterator(size())}). Then, it iterates
* backwards over the list until the matching element is found, or the
* beginning of the list is reached.
*
* @param filter a predicate to search for
* @return the index of the last occurrence of the specified element in
* this list, or -1 if this list does not contain the element
* @throws NullPointerException if passed filter is null
*/
default int lastIndexOf(Predicate<? super E> filter) {
Objects.requireNonNull(filter);
ListIterator<E> it = listIterator(size());
while (it.hasPrevious()) {
E e = it.previous();
if (filter.test(e)) {
return it.nextIndex();
}
}
return -1;
}
-------------
Changes requested by exe-b...@github.com (no known OpenJDK username).
PR Review: https://git.openjdk.org/jdk/pull/18639#pullrequestreview-1985396823
PR Comment: https://git.openjdk.org/jdk/pull/18639#issuecomment-2046339464
PR Review Comment: https://git.openjdk.org/jdk/pull/18639#discussion_r1555586424
PR Review Comment: https://git.openjdk.org/jdk/pull/18639#discussion_r1555192600
PR Review Comment: https://git.openjdk.org/jdk/pull/18639#discussion_r1555192654
PR Review Comment: https://git.openjdk.org/jdk/pull/18639#discussion_r1555194862
