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Posted to commits@commons.apache.org by gg...@apache.org on 2024/11/01 20:43:41 UTC
(commons-collections) 01/02: Added ExtendedIterator and tests
This is an automated email from the ASF dual-hosted git repository.
ggregory pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/commons-collections.git
commit f2db58ec4083f35ca473476d0cd2fea5bd099ca9
Author: Claude Warren <cl...@apache.org>
AuthorDate: Sun Oct 20 10:21:03 2024 +0100
Added ExtendedIterator and tests
---
.../collections4/iterators/ExtendedIterator.java | 197 +++++++++++++++++++++
.../iterators/ExtendedIteratorTest.java | 150 ++++++++++++++++
2 files changed, 347 insertions(+)
diff --git a/src/main/java/org/apache/commons/collections4/iterators/ExtendedIterator.java b/src/main/java/org/apache/commons/collections4/iterators/ExtendedIterator.java
new file mode 100644
index 000000000..b794958fb
--- /dev/null
+++ b/src/main/java/org/apache/commons/collections4/iterators/ExtendedIterator.java
@@ -0,0 +1,197 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections4.iterators;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.stream.Stream;
+
+
+/**
+ * A ExtendedIterator is an Iterator wrapping around a plain
+ * (or presented as plain) Iterator. The wrapping allows the usual
+ * operations found on streams (filtering, concatenating, mapping) to be done on an Iterator derived
+ * from some other source. It also provides convenience methods for common operations.
+ * @param <T> The type of object returned from the iterator.
+ */
+public final class ExtendedIterator<T> implements Iterator<T> {
+ /**
+ * Set to <code>true</code> if this wrapping doesn't permit the use of
+ * {@link #remove()}, otherwise removal is delegated to the base iterator.
+ */
+ private final boolean removeDenied;
+
+ /**
+ * Creates an ExtendedIterator wrapped round <code>it</code>,
+ * which does not permit <code>.remove()</code>
+ * even if <code>it</code> does.
+ * @param it The Iterator to wrap.
+ * @return an Extended iterator on {@code it}
+ * @throws UnsupportedOperationException if remove() is called on the resulting iterator.
+ */
+ public static <T> ExtendedIterator<T> createNoRemove(final Iterator<T> it) {
+ return new ExtendedIterator<>(it, true);
+ }
+
+ /**
+ * Creates an ExtendedIterator wrapped round a {@link Stream}.
+ * The extended iterator does not permit <code>.remove()</code>.
+ * <p>
+ * The stream should not be used directly. The effect of doing so is
+ * undefined.
+ * </p>
+ * @param stream the Stream to create an iterator from.
+ * @return an Extended iterator on the {@code stream} iterator.
+ */
+ public static <T> ExtendedIterator<T> create(final Stream<T> stream) {
+ return new ExtendedIterator<T>(stream.iterator(), true);
+ }
+
+ /**
+ * Flattens an iterator of iterators into an Iterator over the next level values.
+ * Similar to list splicing in lisp.
+ * @param iterators An iterator of iterators.
+ * @return An iterator over the logical concatenation of the inner iterators.
+ */
+ public static <T> ExtendedIterator<T> flatten(final Iterator<Iterator<T>> iterators) {
+ return create(new LazyIteratorChain<T>() {
+
+ @Override
+ protected Iterator<? extends T> nextIterator(final int count) {
+ return iterators.hasNext() ? iterators.next() : null;
+ }
+
+ });
+ }
+
+ /**
+ * Creates an empty Extended iterator.
+ * @return An empty Extended iterator.
+ */
+ public static ExtendedIterator<?> emptyIterator() {
+ return new ExtendedIterator<>(Collections.emptyIterator(), false);
+ }
+
+ /**
+ * Create an ExtendedIterator returning the elements of <code>it</code>.
+ * If <code>it</code> is itself an ExtendedIterator, return that;
+ * otherwise wrap <code>it</code>.
+ * @param it The iterator to wrap.
+ * @return An Extended iterator wrapping {@code it}
+ */
+ public static <T> ExtendedIterator<T> create(final Iterator<T> it) {
+ return it instanceof ExtendedIterator<?>
+ ? (ExtendedIterator<T>) it
+ : new ExtendedIterator<>(it, false);
+ }
+
+ /** the base iterator that we wrap */
+ private final Iterator<? extends T> base;
+
+ /**
+ * Initialise this wrapping with the given base iterator and remove-control.
+ * @param base the base iterator that this iterator wraps
+ * @param removeDenied true if .remove() must throw an exception
+ */
+ private ExtendedIterator(final Iterator<? extends T> base, final boolean removeDenied) {
+ this.base = base;
+ this.removeDenied = removeDenied;
+ }
+
+ @Override
+ public boolean hasNext() {
+ return base.hasNext();
+ }
+
+ @Override
+ public T next() {
+ return base.next();
+ }
+
+ @Override
+ public void forEachRemaining(final Consumer<? super T> action) {
+ base.forEachRemaining(action);
+ }
+
+ @Override
+ public void remove() {
+ if (removeDenied) {
+ throw new UnsupportedOperationException();
+ }
+ base.remove();
+ }
+
+ /**
+ * Returns the next item and removes it from the iterator.
+ * @return the next item from the iterator.
+ */
+ public T removeNext() {
+ T result = next();
+ remove();
+ return result;
+ }
+
+ /**
+ * Chains the {@code other} iterator to the end of this one.
+ * @param other the other iterator to extend this iterator with.
+ * @return A new iterator returning the contents of {@code this} iterator followed by the contents of {@code other} iterator.
+ * @param <X> The type of object returned from the other iterator.
+ */
+ public <X extends T> ExtendedIterator<T> andThen(final Iterator<X> other) {
+ if (base instanceof IteratorChain) {
+ ((IteratorChain<T>) base).addIterator(other);
+ return this;
+ }
+ return new ExtendedIterator<T>(new IteratorChain<T>(this.base, other), this.removeDenied);
+ }
+
+ /**
+ * Filter this iterator using a predicate. Only items for which the predicate returns {@code true} will
+ * be included in the result.
+ * @param predicate The predicate to filter the items with.
+ * @return An iterator filtered by the predicate.
+ */
+ public ExtendedIterator<T> filter(final Predicate<T> predicate) {
+ return new ExtendedIterator<T>(new FilterIterator<>(this, predicate::test), this.removeDenied);
+ }
+
+ /**
+ * Map the elements of the iterator to a now type.
+ * @param function The function to map elements of {@code <T>} to type {@code <U>}.
+ * @return An Extended iterator that returns a {@code <U>} for very {@code <T>} in the original iterator.
+ * @param <U> The object type to return.
+ */
+ public <U> ExtendedIterator<U> map(final Function<T, U> function) {
+ return new ExtendedIterator<U>(new TransformIterator<>(this, function::apply), false);
+ }
+
+ /**
+ * A method to add the remaining elements in the iterator an arbitrary collection.
+ * This method consumes the iterator.
+ * @param collection THe collection to add elements to.
+ * @return the {@code collection} with the elements added.
+ * @param <U> A collection of objects of type {@code <T>}.
+ */
+ public <U extends Collection<T>> U addTo(final U collection) {
+ this.forEachRemaining(collection::add);
+ return collection;
+ }
+}
diff --git a/src/test/java/org/apache/commons/collections4/iterators/ExtendedIteratorTest.java b/src/test/java/org/apache/commons/collections4/iterators/ExtendedIteratorTest.java
new file mode 100644
index 000000000..936290511
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/iterators/ExtendedIteratorTest.java
@@ -0,0 +1,150 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.iterators;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Function;
+import java.util.function.Predicate;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class ExtendedIteratorTest {
+ /**
+ * Collection of {@link Integer}s
+ */
+ private List<Integer> collectionA;
+
+ @BeforeEach
+ public void setUp() {
+ collectionA = new ArrayList<>();
+ collectionA.add(1);
+ collectionA.add(2);
+ collectionA.add(3);
+ collectionA.add(4);
+ collectionA.add(5);
+ collectionA.add(6);
+ }
+
+ @Test
+ public void testCreateNoRemove() {
+ Iterator<Integer> iter = ExtendedIterator.createNoRemove(collectionA.iterator());
+ assertThrows(UnsupportedOperationException.class, iter::remove);
+ }
+
+ @Test
+ public void testCreateWithStream() {
+ Iterator<Integer> iter = ExtendedIterator.create(collectionA.stream());
+ assertThrows(UnsupportedOperationException.class, iter::remove);
+ List<Integer> actual = new ArrayList<>();
+ iter.forEachRemaining(actual::add);
+ assertEquals(collectionA, actual);
+ }
+
+ @Test
+ public void testFlatten() {
+ Iterator<Iterator<Integer>> iteratorIterator = Arrays.asList(
+ Arrays.asList(1, 2, 3).iterator(),
+ Arrays.asList(4, 5, 6).iterator()
+ ).iterator();
+ Iterator<Integer> iter = ExtendedIterator.flatten(iteratorIterator);
+ List<Integer> actual = new ArrayList<>();
+ iter.forEachRemaining(actual::add);
+ assertEquals(collectionA, actual);
+ }
+
+ @Test
+ public void testEmptyIterator() {
+ assertFalse(ExtendedIterator.emptyIterator().hasNext());
+ }
+
+ @Test
+ public void testCreate() {
+ Iterator<Integer> iter = ExtendedIterator.create(collectionA.iterator());
+ List<Integer> actual = new ArrayList<>();
+ iter.forEachRemaining(actual::add);
+ assertEquals(collectionA, actual);
+ }
+
+ @Test
+ public void testRemove() {
+ Iterator<Integer> iter = ExtendedIterator.create(collectionA.iterator());
+ Integer i = iter.next();
+ iter.remove();
+ assertFalse(collectionA.contains(i));
+ List<Integer> actual = new ArrayList<>();
+ iter.forEachRemaining(actual::add);
+ assertEquals(collectionA, actual);
+ }
+
+ @Test
+ public void testRemoveNext() {
+ ExtendedIterator<Integer> iter = ExtendedIterator.create(collectionA.iterator());
+ Integer i = iter.removeNext();
+ assertFalse(collectionA.contains(i));
+ List<Integer> actual = new ArrayList<>();
+ iter.forEachRemaining(actual::add);
+ assertEquals(collectionA, actual);
+ }
+
+ @Test
+ public void testAndThen() {
+ Iterator<Integer> iter1 = Arrays.asList(1, 2, 3).iterator();
+ Iterator<Integer> iter2 = Arrays.asList(4, 5, 6).iterator();
+
+ ExtendedIterator<Integer> underTest = ExtendedIterator.create(iter1).andThen(iter2);
+ List<Integer> actual = new ArrayList<>();
+ underTest.forEachRemaining(actual::add);
+ assertEquals(collectionA, actual);
+ }
+
+ @Test
+ public void testFilter() {
+ List<Integer> expected = Arrays.asList(2, 4, 6);
+ Predicate<Integer> predicate = i -> i % 2 == 0;
+ ExtendedIterator<Integer> underTest = ExtendedIterator.create(collectionA.iterator()).filter(predicate);
+ List<Integer> actual = new ArrayList<>();
+ underTest.forEachRemaining(actual::add);
+ assertEquals(expected, actual);
+ }
+
+ @Test
+ public void testMap() {
+ List<Double> expected = Arrays.asList(0.5, 1., 1.5, 2.0, 2.5, 3.0);
+ Function<Integer, Double> function = i -> i / 2.0;
+ ExtendedIterator<Double> underTest = ExtendedIterator.create(collectionA.iterator()).map(function);
+ List<Double> actual = new ArrayList<>();
+ underTest.forEachRemaining(actual::add);
+ assertEquals(expected, actual);
+ }
+
+ @Test
+ public void testAddTo() {
+ List<Integer> expected = new ArrayList<>(collectionA);
+ expected.addAll(collectionA);
+ List<Integer> actual = ExtendedIterator.create(collectionA.iterator()).addTo(new ArrayList<>(collectionA));
+ assertEquals(expected, actual);
+ }
+}