oshi.util.MapUtil Maven / Gradle / Ivy
/**
* Oshi (https://github.com/oshi/oshi)
*
* Copyright (c) 2010 - 2018 The Oshi Project Team
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Maintainers:
* dblock[at]dblock[dot]org
* widdis[at]gmail[dot]com
* enrico.bianchi[at]gmail[dot]com
*
* Contributors:
* https://github.com/oshi/oshi/graphs/contributors
*/
package oshi.util;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
/**
* Allow Java 8 features on Java 7 HashMaps
*
* @author widdis[at]gmail[dot]com
*/
public class MapUtil {
private MapUtil() {
}
/**
* Returns the value to which the specified key is mapped, or defaultValue
* if this map contains no mapping for the key.
*
* @param
* The map key type
* @param
* The map value type
* @param map
* the map to use
* @param key
* the key whose associated value is to be returned
* @param defaultValue
* the default mapping of the key
* @return the value to which the specified key is mapped, or defaultValue
* if this map contains no mapping for the key
*/
public static V getOrDefault(Map map, K key, V defaultValue) {
synchronized (map) {
V value = map.get(key);
if (value != null) {
return value;
}
return defaultValue;
}
}
/**
* If the specified key is not already associated with a value (or is mapped
* to null) associates it with the given value and returns null, else
* returns the current value.
*
* @param
* The map key type
* @param
* The map value type
* @param map
* the map to use
* @param key
* key with which the specified value is to be associated
* @param value
* value to be associated with the specified key
* @return the previous value associated with the specified key, or null if
* there was no mapping for the key. (A null return can also
* indicate that the map previously associated null with the key, if
* the implementation supports null values.)
*/
public static V putIfAbsent(Map map, K key, V value) {
synchronized (map) {
V existingValue = map.get(key);
if (existingValue != null) {
return existingValue;
}
map.put(key, value);
return null;
}
}
/**
* If the specified key is not already associated with a value (or is mapped
* to null) associates it with a new List and returns it, else returns the
* current value.
*
* @param
* The map key type
* @param
* The map value type in the list
* @param map
* the map to use
* @param key
* key with which the specified value is to be associated
* @return the previous value associated with the specified key, or a new
* list
*/
public static List createNewListIfAbsent(Map> map, K key) {
synchronized (map) {
List value = map.get(key);
if (value != null) {
return value;
}
value = new ArrayList<>();
map.put(key, value);
return value;
}
}
}