src/mdo/java/ImmutableCollections.java

/*
 * 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 ${package};

import java.io.Serializable;
import java.util.AbstractList;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Properties;
import java.util.RandomAccess;
import java.util.Set;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;

class ImmutableCollections {

    private static final List<?> EMPTY_LIST = new AbstractImmutableList<Object>() {
        @Override
        public Object get(int index) {
            throw new IndexOutOfBoundsException();
        }

        @Override
        public int size() {
            return 0;
        }
    };

    private static final Map<?, ?> EMPTY_MAP = new AbstractImmutableMap<Object, Object>() {
        @Override
        public Set<Entry<Object, Object>> entrySet() {
            return new AbstractImmutableSet<Entry<Object, Object>>() {
                @Override
                public Iterator<Entry<Object, Object>> iterator() {
                    return new Iterator<Entry<Object, Object>>() {
                        @Override
                        public boolean hasNext() {
                            return false;
                        }

                        @Override
                        public Entry<Object, Object> next() {
                            throw new NoSuchElementException();
                        }
                    };
                }

                @Override
                public int size() {
                    return 0;
                }
            };
        }
    };

    static <E> List<E> copy(Collection<E> collection) {
        if (collection == null) {
            return emptyList();
        } else if (collection instanceof AbstractImmutableList) {
            return (List<E>) collection;
        } else {
            switch (collection.size()) {
                case 0:
                    return emptyList();
                case 1:
                    return singletonList(collection.iterator().next());
                case 2:
                    Iterator<E> it = collection.iterator();
                    return new List2<>(it.next(), it.next());
                default:
                    return new ListN<>(collection);
            }
        }
    }

    @SuppressWarnings("unchecked")
    static <E> List<E> emptyList() {
        return (List<E>) EMPTY_LIST;
    }

    static <E> List<E> singletonList(E element) {
        return new List1<>(element);
    }

    static <K, V> Map<K, V> copy(Map<K, V> map) {
        if (map == null) {
            return emptyMap();
        } else if (map instanceof AbstractImmutableMap) {
            return map;
        } else {
            switch (map.size()) {
                case 0:
                    return emptyMap();
                case 1:
                    Map.Entry<K, V> entry = map.entrySet().iterator().next();
                    return singletonMap(entry.getKey(), entry.getValue());
                default:
                    return new MapN<>(map);
            }
        }
    }

    @SuppressWarnings("unchecked")
    static <K, V> Map<K, V> emptyMap() {
        return (Map<K, V>) EMPTY_MAP;
    }

    static <K, V> Map<K, V> singletonMap(K key, V value) {
        return new Map1<>(key, value);
    }

    static Properties copy(Properties properties) {
        if (properties instanceof ROProperties) {
            return properties;
        }
        return new ROProperties(properties);
    }

    private static class List1<E> extends AbstractImmutableList<E> {
        private final E element;

        private List1(E element) {
            this.element = element;
        }

        @Override
        public E get(int index) {
            if (index == 0) {
                return element;
            }
            throw outOfBounds(index);
        }

        @Override
        public int size() {
            return 1;
        }
    }

    private static class List2<E> extends AbstractImmutableList<E> {
        private final E element1;
        private final E element2;

        private List2(E element1, E element2) {
            this.element1 = element1;
            this.element2 = element2;
        }

        @Override
        public E get(int index) {
            if (index == 0) {
                return element1;
            } else if (index == 1) {
                return element2;
            }
            throw outOfBounds(index);
        }

        @Override
        public int size() {
            return 2;
        }
    }

    private static class ListN<E> extends AbstractImmutableList<E> {
        private final Object[] elements;

        private ListN(Collection<E> elements) {
            this.elements = elements.toArray();
        }

        @SuppressWarnings("unchecked")
        @Override
        public E get(int index) {
            return (E) elements[index];
        }

        @Override
        public int size() {
            return elements.length;
        }
    }

    private abstract static class AbstractImmutableList<E> extends AbstractList<E>
            implements RandomAccess, Serializable {
        @Override
        public boolean add(E e) {
            throw uoe();
        }

        @Override
        public boolean remove(Object o) {
            throw uoe();
        }

        @Override
        public boolean addAll(Collection<? extends E> c) {
            throw uoe();
        }

        @Override
        public boolean removeAll(Collection<?> c) {
            throw uoe();
        }

        @Override
        public boolean retainAll(Collection<?> c) {
            throw uoe();
        }

        @Override
        public void clear() {
            throw uoe();
        }

        @Override
        public boolean removeIf(Predicate<? super E> filter) {
            throw uoe();
        }

        @Override
        public void replaceAll(UnaryOperator<E> operator) {
            throw uoe();
        }

        @Override
        public void sort(Comparator<? super E> c) {
            throw uoe();
        }

        @Override
        public Iterator<E> iterator() {
            return new Itr(0);
        }

        @Override
        public ListIterator<E> listIterator() {
            return new Itr(0);
        }

        @Override
        public ListIterator<E> listIterator(int index) {
            if (index < 0 || index > size()) {
                throw outOfBounds(index);
            }
            return new Itr(index);
        }

        @Override
        public List<E> subList(int fromIndex, int toIndex) {
            if (fromIndex < 0) {
                throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
            }
            if (toIndex > size()) {
                throw new IndexOutOfBoundsException("toIndex = " + toIndex);
            }
            if (fromIndex > toIndex) {
                throw new IllegalArgumentException("fromIndex(" + fromIndex + ") > toIndex(" + toIndex + ")");
            }
            return new SubList(fromIndex, toIndex);
        }

        protected IndexOutOfBoundsException outOfBounds(int index) {
            return new IndexOutOfBoundsException("Index: " + index + ", Size: " + size());
        }

        private class SubList extends AbstractImmutableList<E> {
            private final int fromIndex;
            private final int toIndex;

            private SubList(int fromIndex, int toIndex) {
                this.fromIndex = fromIndex;
                this.toIndex = toIndex;
            }

            @Override
            public E get(int index) {
                if (index < 0 || index > size()) {
                    throw outOfBounds(index);
                }
                return AbstractImmutableList.this.get(fromIndex + index);
            }

            @Override
            public int size() {
                return toIndex - fromIndex;
            }
        }

        private class Itr implements ListIterator<E> {
            int index;

            private Itr(int index) {
                this.index = index;
            }

            @Override
            public boolean hasNext() {
                return index < size();
            }

            @Override
            public E next() {
                return get(index++);
            }

            @Override
            public boolean hasPrevious() {
                return index > 0;
            }

            @Override
            public E previous() {
                return get(--index);
            }

            @Override
            public int nextIndex() {
                return index;
            }

            @Override
            public int previousIndex() {
                return index - 1;
            }

            @Override
            public void remove() {
                throw uoe();
            }

            @Override
            public void set(E e) {
                throw uoe();
            }

            @Override
            public void add(E e) {
                throw uoe();
            }
        }
    }

    private static class ROProperties extends Properties {
        private ROProperties(Properties props) {
            super();
            if (props != null) {
                // Do not use super.putAll, as it may delegate to put which throws an UnsupportedOperationException
                for (Map.Entry<Object, Object> e : props.entrySet()) {
                    super.put(e.getKey(), e.getValue());
                }
            }
        }

        @Override
        public Object put(Object key, Object value) {
            throw uoe();
        }

        @Override
        public Object remove(Object key) {
            throw uoe();
        }

        @Override
        public void putAll(Map<?, ?> t) {
            throw uoe();
        }

        @Override
        public void clear() {
            throw uoe();
        }

        @Override
        public void replaceAll(BiFunction<? super Object, ? super Object, ?> function) {
            throw uoe();
        }

        @Override
        public Object putIfAbsent(Object key, Object value) {
            throw uoe();
        }

        @Override
        public boolean remove(Object key, Object value) {
            throw uoe();
        }

        @Override
        public boolean replace(Object key, Object oldValue, Object newValue) {
            throw uoe();
        }

        @Override
        public Object replace(Object key, Object value) {
            throw uoe();
        }

        @Override
        public Object computeIfAbsent(Object key, Function<? super Object, ?> mappingFunction) {
            throw uoe();
        }

        @Override
        public Object computeIfPresent(Object key, BiFunction<? super Object, ? super Object, ?> remappingFunction) {
            throw uoe();
        }

        @Override
        public Object compute(Object key, BiFunction<? super Object, ? super Object, ?> remappingFunction) {
            throw uoe();
        }

        @Override
        public Object merge(Object key, Object value, BiFunction<? super Object, ? super Object, ?> remappingFunction) {
            throw uoe();
        }
    }

    private static class Map1<K, V> extends AbstractImmutableMap<K, V> {
        private final Entry<K, V> entry;

        private Map1(K key, V value) {
            this.entry = new SimpleImmutableEntry<>(key, value);
        }

        @Override
        public Set<Entry<K, V>> entrySet() {
            return new AbstractImmutableSet<Entry<K, V>>() {
                @Override
                public Iterator<Entry<K, V>> iterator() {
                    return new Iterator<Entry<K, V>>() {
                        int index = 0;

                        @Override
                        public boolean hasNext() {
                            return index == 0;
                        }

                        @Override
                        public Entry<K, V> next() {
                            if (index++ == 0) {
                                return entry;
                            }
                            throw new NoSuchElementException();
                        }
                    };
                }

                @Override
                public int size() {
                    return 1;
                }
            };
        }
    }

    private static class MapN<K, V> extends AbstractImmutableMap<K, V> {
        private final Object[] entries;

        private MapN(Map<K, V> map) {
            entries = map != null
                    ? map.entrySet().stream()
                            .map(e -> new SimpleImmutableEntry<>(e.getKey(), e.getValue()))
                            .toArray()
                    : new Object[0];
        }

        @Override
        public Set<Entry<K, V>> entrySet() {
            return new AbstractImmutableSet<Entry<K, V>>() {
                @Override
                public Iterator<Entry<K, V>> iterator() {
                    return new Iterator<Entry<K, V>>() {
                        int index = 0;

                        @Override
                        public boolean hasNext() {
                            return index < entries.length;
                        }

                        @SuppressWarnings("unchecked")
                        @Override
                        public Entry<K, V> next() {
                            if (index < entries.length) {
                                return (Entry<K, V>) entries[index++];
                            }
                            throw new NoSuchElementException();
                        }
                    };
                }

                @Override
                public int size() {
                    return entries.length;
                }
            };
        }
    }

    private abstract static class AbstractImmutableMap<K, V> extends AbstractMap<K, V> implements Serializable {
        @Override
        public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
            throw uoe();
        }

        @Override
        public V putIfAbsent(K key, V value) {
            throw uoe();
        }

        @Override
        public boolean remove(Object key, Object value) {
            throw uoe();
        }

        @Override
        public boolean replace(K key, V oldValue, V newValue) {
            throw uoe();
        }

        @Override
        public V replace(K key, V value) {
            throw uoe();
        }

        @Override
        public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
            throw uoe();
        }

        @Override
        public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
            throw uoe();
        }

        @Override
        public V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
            throw uoe();
        }

        @Override
        public V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
            throw uoe();
        }
    }

    private abstract static class AbstractImmutableSet<E> extends AbstractSet<E> implements Serializable {
        @Override
        public boolean removeAll(Collection<?> c) {
            throw uoe();
        }

        @Override
        public boolean add(E e) {
            throw uoe();
        }

        @Override
        public boolean remove(Object o) {
            throw uoe();
        }

        @Override
        public boolean retainAll(Collection<?> c) {
            throw uoe();
        }

        @Override
        public void clear() {
            throw uoe();
        }

        @Override
        public boolean removeIf(Predicate<? super E> filter) {
            throw uoe();
        }
    }

    private static UnsupportedOperationException uoe() {
        return new UnsupportedOperationException();
    }
}