8266571: Sequenced Collections

Reviewed-by: alanb

src/java.base/share/classes/java/util/ReverseOrderDequeView.java

@@ -0,0 +1,279 @@
+/*
+ * Copyright (c) 2021, 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.util;
+
+import java.util.function.Consumer;
+import java.util.function.IntFunction;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+import jdk.internal.util.ArraysSupport;
+
+/**
+ * Provides a reverse-ordered view of any Deque. Not serializable.
+ */
+class ReverseOrderDequeView<E> implements Deque<E> {
+    final Deque<E> base;
+
+    private ReverseOrderDequeView(Deque<E> deque) {
+        base = deque;
+    }
+
+    public static <T> Deque<T> of(Deque<T> deque) {
+        if (deque instanceof ReverseOrderDequeView<T> rodv) {
+            return rodv.base;
+        } else {
+            return new ReverseOrderDequeView<>(deque);
+        }
+    }
+
+    // ========== Iterable ==========
+
+    public void forEach(Consumer<? super E> action) {
+        for (E e : this)
+            action.accept(e);
+    }
+
+    public Iterator<E> iterator() {
+        return base.descendingIterator();
+    }
+
+    public Spliterator<E> spliterator() {
+        return Spliterators.spliteratorUnknownSize(base.descendingIterator(), 0);
+    }
+
+    // ========== Collection ==========
+
+    public boolean add(E e) {
+        base.addFirst(e);
+        return true;
+    }
+
+    public boolean addAll(Collection<? extends E> c) {
+        boolean modified = false;
+        for (E e : c) {
+            base.addFirst(e);
+            modified = true;
+        }
+        return modified;
+    }
+
+    public void clear() {
+        base.clear();
+    }
+
+    public boolean contains(Object o) {
+        return base.contains(o);
+    }
+
+    public boolean containsAll(Collection<?> c) {
+        return base.containsAll(c);
+    }
+
+    public boolean isEmpty() {
+        return base.isEmpty();
+    }
+
+    public Stream<E> parallelStream() {
+        return StreamSupport.stream(spliterator(), true);
+    }
+
+    // copied from AbstractCollection
+    public boolean remove(Object o) {
+        Iterator<E> it = iterator();
+        if (o==null) {
+            while (it.hasNext()) {
+                if (it.next()==null) {
+                    it.remove();
+                    return true;
+                }
+            }
+        } else {
+            while (it.hasNext()) {
+                if (o.equals(it.next())) {
+                    it.remove();
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    // copied from AbstractCollection
+    public boolean removeAll(Collection<?> c) {
+        Objects.requireNonNull(c);
+        boolean modified = false;
+        Iterator<?> it = iterator();
+        while (it.hasNext()) {
+            if (c.contains(it.next())) {
+                it.remove();
+                modified = true;
+            }
+        }
+        return modified;
+    }
+
+    // copied from AbstractCollection
+    public boolean retainAll(Collection<?> c) {
+        Objects.requireNonNull(c);
+        boolean modified = false;
+        Iterator<E> it = iterator();
+        while (it.hasNext()) {
+            if (!c.contains(it.next())) {
+                it.remove();
+                modified = true;
+            }
+        }
+        return modified;
+    }
+
+    public int size() {
+        return base.size();
+    }
+
+    public Stream<E> stream() {
+        return StreamSupport.stream(spliterator(), false);
+    }
+
+    public Object[] toArray() {
+        return ArraysSupport.reverse(base.toArray());
+    }
+
+    @SuppressWarnings("unchecked")
+    public <T> T[] toArray(T[] a) {
+        return ArraysSupport.toArrayReversed(base, a);
+    }
+
+    public <T> T[] toArray(IntFunction<T[]> generator) {
+        return ArraysSupport.reverse(base.toArray(generator));
+    }
+
+    // copied from AbstractCollection
+    public String toString() {
+        Iterator<E> it = iterator();
+        if (! it.hasNext())
+            return "[]";
+
+        StringBuilder sb = new StringBuilder();
+        sb.append('[');
+        for (;;) {
+            E e = it.next();
+            sb.append(e == this ? "(this Collection)" : e);
+            if (! it.hasNext())
+                return sb.append(']').toString();
+            sb.append(',').append(' ');
+        }
+    }
+
+    // ========== Deque and Queue ==========
+
+    public void addFirst(E e) {
+        base.addLast(e);
+    }
+
+    public void addLast(E e) {
+        base.addFirst(e);
+    }
+
+    public Iterator<E> descendingIterator() {
+        return base.iterator();
+    }
+
+    public E element() {
+        return base.getLast();
+    }
+
+    public E getFirst() {
+        return base.getLast();
+    }
+
+    public E getLast() {
+        return base.getFirst();
+    }
+
+    public boolean offer(E e) {
+        return base.offerFirst(e);
+    }
+
+    public boolean offerFirst(E e) {
+        return base.offerLast(e);
+    }
+
+    public boolean offerLast(E e) {
+        return base.offerFirst(e);
+    }
+
+    public E peek() {
+        return base.peekLast();
+    }
+
+    public E peekFirst() {
+        return base.peekLast();
+    }
+
+    public E peekLast() {
+        return base.peekFirst();
+    }
+
+    public E poll() {
+        return base.pollLast();
+    }
+
+    public E pollFirst() {
+        return base.pollLast();
+    }
+
+    public E pollLast() {
+        return base.pollFirst();
+    }
+
+    public E pop() {
+        return base.removeLast();
+    }
+
+    public void push(E e) {
+        base.addLast(e);
+    }
+
+    public E remove() {
+        return base.removeLast();
+    }
+
+    public E removeFirst() {
+        return base.removeLast();
+    }
+
+    public E removeLast() {
+        return base.removeFirst();
+    }
+
+    public boolean removeFirstOccurrence(Object o) {
+        return base.removeLastOccurrence(o);
+    }
+
+    public boolean removeLastOccurrence(Object o) {
+        return base.removeFirstOccurrence(o);
+    }
+}