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  /*
   * Copyright SpringSource Inc 2007,2009.
   *
   * 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.springsource.util.common;
 
 import java.util.List;
 import java.util.Map;
Miscellaneous collection utility methods.

Author(s):
Juergen Hoeller
Rob Harrop
 
 public abstract class CollectionUtils {

Return true if the supplied Collection is null or empty. Otherwise, return false.

Parameters:
collection the Collection to check
Returns:
whether the given Collection is empty
 
 	public static boolean isEmpty(Collection<?> collection) {
 		return (collection == null || collection.isEmpty());
 	}

Return true if the supplied Map is null or empty. Otherwise, return false.

Parameters:
map the Map to check
Returns:
whether the given Map is empty
 
 	public static boolean isEmpty(Map<?,?> map) {
 		return (map == null || map.isEmpty());
 	}

Convert the supplied array into a List.

A null source value will be converted to an empty List.

Parameters:
<T> the type of elements of the list
source the array
Returns:
the converted List result
See also:
ObjectUtils.toObjectArray(java.lang.Object)
 
 	public static <T> List<T> arrayToList(T[] source) {
 		return Arrays.asList(source);
 	}

Merge the given array into the given Collection.

Parameters:
<T> type of elements of array
array the array to merge (may be null)
collection the target Collection to merge the array into
 
 	public static <T> void mergeArrayIntoCollection(T[] arrayCollection<T> collection) {
 		if (collection == null) {
 			throw new IllegalArgumentException("Collection must not be null");
 		}
 		for (int i = 0; i < array.lengthi++) {
 			collection.add(array[i]);
 		}
 	}

Merge the given Properties instance into the given Map, copying all properties (key-value pairs) over.

Uses Properties.propertyNames() to even catch default properties linked into the original Properties instance.

Parameters:
props the Properties instance to merge (may be null)
map the target Map to merge the properties into
 
 	public static void mergePropertiesIntoMap(Properties propsMap<? super String, ? super Stringmap) {
 		if (map == null) {
 			throw new IllegalArgumentException("Map must not be null");
 		}
 		if (props != null) {
 			for (Enumeration<?> en = props.propertyNames(); en.hasMoreElements();) {
 				String key = (Stringen.nextElement();
 				map.put(keyprops.getProperty(key));
 			}
		}
	}


Check whether the given Iterator contains the given element.

Parameters:
iterator the Iterator to check
element the element to look for
Returns:
true if found, false else
	public static boolean contains(Iterator<?> iteratorObject element) {
		if (iterator != null) {
			while (iterator.hasNext()) {
				Object candidate = iterator.next();
				if (ObjectUtils.nullSafeEquals(candidateelement)) {
					return true;
				}
			}
		}
		return false;
	}

Check whether the given Enumeration contains the given element.

Parameters:
enumeration the Enumeration to check
element the element to look for
Returns:
true if found, false else
	public static boolean contains(Enumeration<?> enumerationObject element) {
		if (enumeration != null) {
			while (enumeration.hasMoreElements()) {
				Object candidate = enumeration.nextElement();
				if (ObjectUtils.nullSafeEquals(candidateelement)) {
					return true;
				}
			}
		}
		return false;
	}

Check whether the given Collection contains the given element instance.

Enforces the given instance to be present, rather than returning true for an equal element as well.

Parameters:
collection the Collection to check
element the element to look for
Returns:
true if found, false else
	public static boolean containsInstance(Collection<?> collectionObject element) {
		if (collection != null) {
			for (Iterator<?> it = collection.iterator(); it.hasNext();) {
				Object candidate = it.next();
				if (candidate == element) {
					return true;
				}
			}
		}
		return false;
	}

Return true if any element in 'candidates' is contained in 'source'; otherwise returns false.

Parameters:
source the source Collection
candidates the candidates to search for
Returns:
whether any of the candidates has been found
	public static boolean containsAny(Collection<?> sourceCollection<?> candidates) {
		if (isEmpty(source) || isEmpty(candidates)) {
			return false;
		}
		for (Iterator<?> it = candidates.iterator(); it.hasNext();) {
			if (source.contains(it.next())) {
				return true;
			}
		}
		return false;
	}

Return the first element in 'candidates' that is contained in 'source'. If no element in 'candidates' is present in 'source' returns null. Iteration order is java.util.Collection implementation specific.

Parameters:
source the source Collection
candidates the candidates to search for
Returns:
the first present object, or null if not found
	public static Object findFirstMatch(Collection<?> sourceCollection<?> candidates) {
		if (isEmpty(source) || isEmpty(candidates)) {
			return null;
		}
		for (Iterator<?> it = candidates.iterator(); it.hasNext();) {
			Object candidate = it.next();
			if (source.contains(candidate)) {
				return candidate;
			}
		}
		return null;
	}

Find a single value of the given type in the given Collection.

Parameters:
collection the Collection to search
type the type to look for
Returns:
a value of the given type found if there is a clear match, or null if none or more than one such value found
	public static Object findValueOfType(Collection<?> collectionClass<?> type) {
		if (isEmpty(collection)) {
			return null;
		}
		Object value = null;
		for (Iterator<?> it = collection.iterator(); it.hasNext();) {
			Object obj = it.next();
			if (type == null || type.isInstance(obj)) {
				if (value != null) {
					// More than one value found... no clear single value.
					return null;
				}
				value = obj;
			}
		}
		return value;
	}

Find a single value of one of the given types in the given Collection: searching the Collection for a value of the first type, then searching for a value of the second type, etc.

Parameters:
collection the collection to search
types the types to look for, in prioritized order
Returns:
a value of one of the given types found if there is a clear match, or null if none or more than one such value found
	public static Object findValueOfType(Collection<?> collectionClass<?>[] types) {
		if (isEmpty(collection) || ObjectUtils.isEmpty(types)) {
			return null;
		}
		for (int i = 0; i < types.lengthi++) {
			Object value = findValueOfType(collectiontypes[i]);
			if (value != null) {
				return value;
			}
		}
		return null;
	}

Determine whether the given Collection only contains a single unique object.

Parameters:
collection the Collection to check
Returns:
true if the collection contains a single reference or multiple references to the same instance, false else
	public static boolean hasUniqueObject(Collection<?> collection) {
		if (isEmpty(collection)) {
			return false;
		}
		boolean hasCandidate = false;
		Object candidate = null;
		for (Iterator<?> it = collection.iterator(); it.hasNext();) {
			Object elem = it.next();
			if (!hasCandidate) {
				hasCandidate = true;
				candidate = elem;
			}
			else if (candidate != elem) {
				return false;
			}
		}
		return true;
	}
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