1/*
2 * Copyright (c) 2017, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23package org.graalvm.compiler.core.common.util;
24
25import java.util.AbstractList;
26import java.util.List;
27import java.util.RandomAccess;
28
29/**
30 * A {@code ReversedList} is a view on an other list with the elements in reverse order.
31 *
32 * This implementation is made for {@link RandomAccess} lists.
33 */
34public class ReversedList<T> extends AbstractList<T> implements RandomAccess {
35    private final List<T> original;
36
37    public ReversedList(List<T> original) {
38        assert original instanceof RandomAccess;
39        this.original = original;
40    }
41
42    @Override
43    public T get(int index) {
44        return original.get(original.size() - index - 1);
45    }
46
47    @Override
48    public int size() {
49        return original.size();
50    }
51
52    /**
53     * Creates a list that is a view on {@code list} in reverse order.
54     */
55    public static <T> ReversedList<T> reversed(List<T> list) {
56        return new ReversedList<>(list);
57    }
58}
59