Utility methods for operating on memory-efficient lists. All lists of size 0 or 1 are assumed to be immutable.
/*
* Copyright 2009 Google Inc.
*
* Licensed 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.
*/
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
/**
* Utility methods for operating on memory-efficient lists. All lists of size 0
* or 1 are assumed to be immutable. All lists of size greater than 1 are
* assumed to be mutable.
*/
public class Lists {
private static final Class<?> MULTI_LIST_CLASS = ArrayList.class;
private static final Class<?> SINGLETON_LIST_CLASS = Collections.singletonList(
null).getClass();
public static <T> List<T> add(List<T> list, int index, T toAdd) {
switch (list.size()) {
case 0:
// Empty -> Singleton
if (index != 0) {
throw newIndexOutOfBounds(list, index);
}
return Collections.singletonList(toAdd);
case 1: {
// Singleton -> ArrayList
List<T> result = new ArrayList<T>(2);
switch (index) {
case 0:
result.add(toAdd);
result.add(list.get(0));
return result;
case 1:
result.add(list.get(0));
result.add(toAdd);
return result;
default:
throw newIndexOutOfBounds(list, index);
}
}
default:
// ArrayList
list.add(index, toAdd);
return list;
}
}
public static <T> List<T> add(List<T> list, T toAdd) {
switch (list.size()) {
case 0:
// Empty -> Singleton
return Collections.singletonList(toAdd);
case 1: {
// Singleton -> ArrayList
List<T> result = new ArrayList<T>(2);
result.add(list.get(0));
result.add(toAdd);
return result;
}
default:
// ArrayList
list.add(toAdd);
return list;
}
}
public static <T> List<T> addAll(List<T> list, int index, List<T> toAdd) {
switch (toAdd.size()) {
case 0:
// No-op.
return list;
case 1:
// Add one element.
return add(list, index, toAdd.get(0));
default:
// True list merge, result >= 2.
switch (list.size()) {
case 0:
if (index != 0) {
throw newIndexOutOfBounds(list, index);
}
return new ArrayList<T>(toAdd);
case 1: {
List<T> result = new ArrayList<T>(1 + toAdd.size());
switch (index) {
case 0:
result.addAll(toAdd);
result.add(list.get(0));
return result;
case 1:
result.add(list.get(0));
result.addAll(toAdd);
return result;
default:
throw newIndexOutOfBounds(list, index);
}
}
default:
list.addAll(index, toAdd);
return list;
}
}
}
public static <T> List<T> addAll(List<T> list, List<T> toAdd) {
switch (toAdd.size()) {
case 0:
// No-op.
return list;
case 1:
// Add one element.
return add(list, toAdd.get(0));
default:
// True list merge, result >= 2.
switch (list.size()) {
case 0:
return new ArrayList<T>(toAdd);
case 1: {
List<T> result = new ArrayList<T>(1 + toAdd.size());
result.add(list.get(0));
result.addAll(toAdd);
return result;
}
default:
list.addAll(toAdd);
return list;
}
}
}
public static <T> List<T> addAll(List<T> list, T... toAdd) {
switch (toAdd.length) {
case 0:
// No-op.
return list;
case 1:
// Add one element.
return add(list, toAdd[0]);
default:
// True list merge, result >= 2.
switch (list.size()) {
case 0:
return new ArrayList<T>(Arrays.asList(toAdd));
case 1: {
List<T> result = new ArrayList<T>(1 + toAdd.length);
result.add(list.get(0));
result.addAll(Arrays.asList(toAdd));
return result;
}
default:
list.addAll(Arrays.asList(toAdd));
return list;
}
}
}
public static <T> List<T> create() {
return Collections.emptyList();
}
public static <T> List<T> create(T item) {
return Collections.singletonList(item);
}
public static <T> List<T> create(T... items) {
switch (items.length) {
case 0:
return create();
case 1:
return create(items[0]);
default:
return new ArrayList<T>(Arrays.asList(items));
}
}
public static <T> List<T> normalize(List<T> list) {
switch (list.size()) {
case 0:
return create();
case 1: {
if (list.getClass() == SINGLETON_LIST_CLASS) {
return list;
}
return create(list.get(0));
}
default:
if (list.getClass() == MULTI_LIST_CLASS) {
return list;
}
return new ArrayList<T>(list);
}
}
@SuppressWarnings("unchecked")
public static <T> List<T> normalizeUnmodifiable(List<T> list) {
if (list.size() < 2) {
return normalize(list);
} else {
return (List<T>) Arrays.asList(list.toArray());
}
}
public static <T> List<T> remove(List<T> list, int toRemove) {
switch (list.size()) {
case 0:
// Empty
throw newIndexOutOfBounds(list, toRemove);
case 1:
// Singleton -> Empty
if (toRemove == 0) {
return Collections.emptyList();
} else {
throw newIndexOutOfBounds(list, toRemove);
}
case 2:
// ArrayList -> Singleton
switch (toRemove) {
case 0:
return Collections.singletonList(list.get(1));
case 1:
return Collections.singletonList(list.get(0));
default:
throw newIndexOutOfBounds(list, toRemove);
}
default:
// ArrayList
list.remove(toRemove);
return list;
}
}
public static <T> List<T> set(List<T> list, int index, T e) {
switch (list.size()) {
case 0:
// Empty
throw newIndexOutOfBounds(list, index);
case 1:
// Singleton
if (index == 0) {
return Collections.singletonList(e);
} else {
throw newIndexOutOfBounds(list, index);
}
default:
// ArrayList
list.set(index, e);
return list;
}
}
public static <T> List<T> sort(List<T> list, Comparator<? super T> sort) {
if (list.size() > 1) {
Collections.sort(list, sort);
}
return list;
}
private static <T> IndexOutOfBoundsException newIndexOutOfBounds(
List<T> list, int index) {
return new IndexOutOfBoundsException("Index: " + index + ", Size: "
+ list.size());
}
}
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