Class SingletonMap

lib/java/util/Collections.java:310–394

    }

    private static final class SingletonMap<K, V> extends AbstractMap<K, V>
            implements Serializable {
        private static final long serialVersionUID = -6979724477215052911L;

        final K k;

        final V v;

        SingletonMap(K key, V value) {
            k = key;
            v = value;
        }

        @Override
        public boolean containsKey(Object key) {
            return k == null ? key == null : k.equals(key);
        }

        @Override
        public boolean containsValue(Object value) {
            return v == null ? value == null : v.equals(value);
        }

        @Override
        public V get(Object key) {
            if (containsKey(key)) {
                return v;
            }
            return null;
        }

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

        @Override
        public Set<Map.Entry<K, V>> entrySet() {
            return new AbstractSet<Map.Entry<K, V>>() {
                @Override
                public boolean contains(Object object) {
                    if (object instanceof Map.Entry) {
                        Map.Entry<?, ?> entry = (Map.Entry<?, ?>) object;
                        return containsKey(entry.getKey())
                                && containsValue(entry.getValue());
                    }
                    return false;
                }

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

                @Override
                public Iterator<Map.Entry<K, V>> iterator() {
                    return new Iterator<Map.Entry<K, V>>() {
                        boolean hasNext = true;