/*
* 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.
*/
package com.rometools.utils;
import java.util.
ArrayList;
import java.util.
List;
public final class
Lists {
private
Lists() {
}
/**
* Returns the list when it is not null. Returns a new list otherwise.
*
* @param list The list to process, can be null
* @return The input list when it is not null, a new list otherwise
*/
public static <T>
List<T>
createWhenNull(final
List<T>
list) {
if (
list == null) {
return new
ArrayList<T>();
} else {
return
list;
}
}
/**
* Creates a new List with the given item as the first entry.
*
* @param item The item to add to the new list
* @return List containing the given item
*/
public static <T>
List<T>
create(final T
item) {
final
List<T>
list = new
ArrayList<T>();
list.
add(
item);
return
list;
}
/**
* Extracts the first entry of the list when it is not null and contains values.
*
* @param list The list to extract the first entry from, can be null
* @return The first entry of the list when it is not null or empty, null otherwise
*/
public static <T> T
firstEntry(final
List<T>
list) {
if (
list != null && !
list.
isEmpty()) {
return
list.
get(0);
} else {
return null;
}
}
/**
* Checks whether the list is null or empty.
*
* @param list The list to check
* @return true when the list is null or empty, false otherwise
*/
public static boolean
isEmpty(final
List<?>
list) {
return
list == null ||
list.
isEmpty();
}
/**
* Checks whether the list is not null and not empty.
*
* @param list The list to check
* @return true when the list is not null and not empty
*/
public static boolean
isNotEmpty(final
List<?>
list) {
return !
isEmpty(
list);
}
/**
* Checks whether the list has the given size. A null list is treated like a list without
* entries.
*
* @param list The list to check
* @param size The size to check
* @return true when the list has the given size or when size = 0 and the list is null, false
* otherwise
*/
public static boolean
sizeIs(final
List<?>
list, final int
size) {
if (
size == 0) {
return
list == null ||
list.
isEmpty();
} else {
return
list != null &&
list.
size() ==
size;
}
}
/**
* Returns null, when the given list is empty or null
*
* @param list The list to process
* @return null when the list is empty or null, the given list otherwise
*/
public static <T>
List<T>
emptyToNull(final
List<T>
list) {
if (
isEmpty(
list)) {
return null;
} else {
return
list;
}
}
}