2 * Copyright (c) 2013 Cisco Systems, Inc. and others. All rights reserved.
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
6 * and is available at http://www.eclipse.org/legal/epl-v10.html
8 package org.opendaylight.yangtools.util;
10 import java.util.ArrayList;
11 import java.util.Collections;
12 import java.util.HashSet;
13 import java.util.List;
17 * Utility methods for lazily instantiated collections. These are useful for situations when we start off with an empty
18 * collection (where Collections.empty() * can be reused), but need to add more things.
20 public final class LazyCollections {
21 private LazyCollections() {
26 * Add an element to a list, potentially transforming the list.
28 * @param <E> the type of elements in the list
29 * @param list Current list
30 * @param obj Object that needs to be added
33 public static <E> List<E> lazyAdd(final List<E> list, final E obj) {
36 switch (list.size()) {
38 return Collections.singletonList(obj);
40 ret = new ArrayList<>(2);
52 * Add an element to a set, potentially transforming the set.
54 * @param <E> the type of elements in the set
55 * @param set Current set
56 * @param obj Object that needs to be added
59 public static <E> Set<E> lazyAdd(final Set<E> set, final E obj) {
64 return Collections.singleton(obj);
66 ret = new HashSet<>(4);