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.List;
15 * Utility methods for lazily instantiated collections. These are useful for
16 * situations when we start off with an empty collection (where Collections.empty()
17 * can be reused), but need to add more things.
19 public final class LazyCollections {
21 private LazyCollections() {
22 throw new UnsupportedOperationException("Utility class should not be instantiated");
26 * Add an element to a list, potentially transforming the list.
28 * @param list Current list
29 * @param obj Object that needs to be added
32 public static <T> List<T> lazyAdd(final List<T> list, final T obj) {
35 switch (list.size()) {
37 return Collections.singletonList(obj);
39 ret = new ArrayList<>(2);