java.util extensions

Table of Contents

• Functional extensions
• Collections
  • Iterator interfaces
  • Iterator implementations
  • Collection wrappers
• Release history

Functional extensions

Classes related to java.util.Function and extensions like Predicate, Consumer and Supplier.

• TriFunction, QuadriFunction

• TriConsumer

• TriPredicate

• Morphing methods like

  • TriFunction#ignoreArg[1-4](…​) morphs a TriFunction to a QuadriFunction

  • TriFunction#withArg[1-3](…​) morphs a TriFunction to a BiFunction.

• Utilities for that in

  • Functions

  • Consumers

  • Predicates,

  • Suppliers

    Things like memoize (to memoize the value of a supplier), closeable (to make a Supplier AutoCloseable) and ignoreArg (to morph a Supplier to a Function that ignores the argument) are provided.

• Consistent equals and hashCode, for the utility functions that produce functional implementations. E.g. the above mentioned ignoreArg* and withArg* are not simply implemented with lambda’s, but also with equals and hashcode based on the source functional class implementation.

Collections

The mihxil-collections module (since 1.18) contains utilities for java.util.Iterator and java.util.Collection, in package org.meeuw.collections. Most of them originate from vpro-shared-util.

Iterator interfaces

• CloseableIterator: an Iterator that is also AutoCloseable. CloseableIterator.of(iterator) wraps any iterator (closing it if it is AutoCloseable itself).

• PeekingIterator: an iterator with a one-element lookahead (peek()), like guava’s, but without the dependency.

• CountedIterator: an iterator that knows its current position (getCount()), and optionally the size of what it iterates (getSize()) and of some 'total' (getTotalSize()), e.g. when it represents a page of a larger result.

• Combinations of these: CloseablePeekingIterator, CountedPeekingIterator.

• CloseableSpliterator: a Spliterator owning a closeable resource.

Iterator implementations

Most of these are wrappers around another iterator, and can be constructed with a (lombok generated) builder.

• BatchedReceiver: presents an API that only supports batched retrieval (paging with offset/max, or some 'resumption token') as one simple Iterator.

  Iterator<String> i = BatchedReceiver.<String>builder()
      .batchGetter((offset, max) -> apiClient.getPage(offset, max).iterator())
      .batchSize(100)
      .build();

• MaxOffsetIterator, CountedMaxOffsetIterator: implements 'offset' and 'max' on top of another iterator.

  MaxOffsetIterator<String> i = MaxOffsetIterator.<String>builder()
      .wrapped(iterator)
      .offset(10)
      .max(20)
      .build();

• FilteringIterator: filters an iterator with a predicate, with optional 'keep alive' callbacks for when many consecutive elements are filtered out.

• TransformingIterator: maps the elements of an iterator with a function.

• SkippingIterator: skips elements based on comparison with the previous one (e.g. to remove consecutive duplicates).

• HeadAdder, TailAdder: add elements at the start or at the end of an iterator (the latter possibly based on the last element).

• MergedSortedIterator: merges several sorted iterators into one sorted iterator. merge(…​) uses a priority queue, mergeInSameThread(…​) doesn’t (so it is also usable with e.g. Hibernate).

• LazyIterator: wraps a Supplier<Iterator>, delaying creation of the actual iterator until it is first used.

• CallbackIterator: calls a callback when iteration is finished.

• WrappedIterator, BasicWrappedIterator: base classes for iterators wrapping another one.

Collection wrappers

• TransformingList, TransformingSortedSet: modifiable views on a collection of other element types, given a 'transformer' and its inverse, a 'producer'. Changes are reflected in the wrapped collection.

• ResortedSortedSet: a modifiable SortedSet view on another collection, with an explicit sort order.

• SortedSetElementWrapper, SortedSetSameElementWrapper: base classes for SortedSet views on a wrapped sorted set.

Release history

Version	date	remarks
2.0	2026-10	Optional<Long> results were replaced by OptionaLong, which is not backwards compatible (only in new collections module)
1.18	2026-08	Having collection module too.
1.17	2026-03	For the 'Throwing-' functional interfaces, there are now also overridden verison of the 'withArgN' and 'ignoreArgN' morphing methods, that remain 'Throwing-' functional interfaces, and throw the same exception as the original functional interface.
1.12	2025-06-26	A.o, introduction of 'CloseableSupplier' and 'UnwrappableSupplier' interfaces,
1.11	2024-05-11
1.10	2023-12
1.0	2020-11-30