javaSE-集合工具类-Collections

public class CollectionsDemo {

	public static void main(String[] args) {

		
		/*
		 * Collections演示。
		 * 1，用于操作集合的工具类。
		 * 2，提供了很多的静态方法。 
		 * 
		 * 比如对list集合排序，二分查找，位置置换。
		 * 对排序的元素进行顺序的逆转。reverseOrder
		 * 还可以获取集合的最大值和最小值。
		 * 最牛叉的是将非同步的集合转成同步的集合 synchronizedXXX
		 * 
		 */
		sortDemo();
		
	}
	//1,演示Collections中的排序。
	public static void sortDemo(){
		
		List list = new ArrayList();
		list.add("abc");
		list.add("aaaaaaa");
		list.add("hahah");
		list.add("cba");
		
		System.out.println(list);
		//排序方法。
//		Collections.sort(list,Collections.reverseOrder());
//		Collections.sort(list,Collections.reverseOrder(new ComparatorByLength()));
		
//		String max = Collections.max(list,new ComparatorByLength());
		String max = myMax(list);
		System.out.println("max="+max);
		System.out.println(list);
		
	}
	
	//模拟一个max方法。获取集合中的最大值。
	public static > T myMax(Collection coll){
		
		Iterator it = coll.iterator();
		//定义一个记录较大值的变量。
		T max = it.next();
		
		while(it.hasNext()){
			
			T temp = it.next();
			if(temp.compareTo(max)>0){
//			if(comp.compare(temp, max)>0){
				max  = temp;
			}
		}
		return max;
		
	}

}

如果collection使用的时候是多线程访问的 用Collections的加锁方法 对Collection加锁

Field Summary

Fields  

Modifier and Type	Field and Description
static List	EMPTY_LIST The empty list (immutable).
static Map	EMPTY_MAP The empty map (immutable).
static Set	EMPTY_SET The empty set (immutable).

Method Summary

Methods  

Modifier and Type	Method and Description
static  boolean	addAll(Collection c, T... elements) Adds all of the specified elements to the specified collection.
static  Queue	asLifoQueue(Deque deque) Returns a view of a Deque as a Last-in-first-out (Lifo) Queue.
static  int	binarySearch(List> list, T key) Searches the specified list for the specified object using the binary search algorithm.
static  int	binarySearch(List list, T key, Comparator c) Searches the specified list for the specified object using the binary search algorithm.
static  Collection	checkedCollection(Collection c, Class type) Returns a dynamically typesafe view of the specified collection.
static  List	checkedList(List list, Class type) Returns a dynamically typesafe view of the specified list.
static  Map	checkedMap(Map m, Class keyType, Class valueType) Returns a dynamically typesafe view of the specified map.
static  Set	checkedSet(Set s, Class type) Returns a dynamically typesafe view of the specified set.
static  SortedMap	checkedSortedMap(SortedMap m, Class keyType, Class valueType) Returns a dynamically typesafe view of the specified sorted map.
static  SortedSet	checkedSortedSet(SortedSet s, Class type) Returns a dynamically typesafe view of the specified sorted set.
static  void	copy(List dest, List src) Copies all of the elements from one list into another.
static boolean	disjoint(Collection c1, Collection c2) Returns true if the two specified collections have no elements in common.
static  Enumeration	emptyEnumeration() Returns an enumeration that has no elements.
static  Iterator	emptyIterator() Returns an iterator that has no elements.
static  List	emptyList() Returns the empty list (immutable).
static  ListIterator	emptyListIterator() Returns a list iterator that has no elements.
static  Map	emptyMap() Returns the empty map (immutable).
static  Set	emptySet() Returns the empty set (immutable).
static  Enumeration	enumeration(Collection c) Returns an enumeration over the specified collection.
static  void	fill(List list, T obj) Replaces all of the elements of the specified list with the specified element.
static int	frequency(Collection c, Object o) Returns the number of elements in the specified collection equal to the specified object.
static int	indexOfSubList(List source, List target) Returns the starting position of the first occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence.
static int	lastIndexOfSubList(List source, List target) Returns the starting position of the last occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence.
static  ArrayList	list(Enumeration e) Returns an array list containing the elements returned by the specified enumeration in the order they are returned by the enumeration.
static >  T	max(Collection coll) Returns the maximum element of the given collection, according to the natural ordering of its elements.
static  T	max(Collection coll, Comparator comp) Returns the maximum element of the given collection, according to the order induced by the specified comparator.
static >  T	min(Collection coll) Returns the minimum element of the given collection, according to the natural ordering of its elements.
static  T	min(Collection coll, Comparator comp) Returns the minimum element of the given collection, according to the order induced by the specified comparator.
static  List	nCopies(int n, T o) Returns an immutable list consisting of n copies of the specified object.
static  Set	newSetFromMap(Map map) Returns a set backed by the specified map.
static  boolean	replaceAll(List list, T oldVal, T newVal) Replaces all occurrences of one specified value in a list with another.
static void	reverse(List list) Reverses the order of the elements in the specified list.
static  Comparator	reverseOrder() Returns a comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface.
static  Comparator	reverseOrder(Comparator cmp) Returns a comparator that imposes the reverse ordering of the specified comparator.
static void	rotate(List list, int distance) Rotates the elements in the specified list by the specified distance.
static void	shuffle(List list) Randomly permutes the specified list using a default source of randomness.
static void	shuffle(List list, Random rnd) Randomly permute the specified list using the specified source of randomness.
static  Set	singleton(T o) Returns an immutable set containing only the specified object.
static  List	singletonList(T o) Returns an immutable list containing only the specified object.
static  Map	singletonMap(K key, V value) Returns an immutable map, mapping only the specified key to the specified value.
static >  void	sort(List list) Sorts the specified list into ascending order, according to the natural ordering of its elements.
static  void	sort(List list, Comparator c) Sorts the specified list according to the order induced by the specified comparator.
static void	swap(List list, int i, int j) Swaps the elements at the specified positions in the specified list.
static  Collection	synchronizedCollection(Collection c) Returns a synchronized (thread-safe) collection backed by the specified collection.
static  List	synchronizedList(List list) Returns a synchronized (thread-safe) list backed by the specified list.
static  Map	synchronizedMap(Map m) Returns a synchronized (thread-safe) map backed by the specified map.
static  Set	synchronizedSet(Set s) Returns a synchronized (thread-safe) set backed by the specified set.
static  SortedMap	synchronizedSortedMap(SortedMap m) Returns a synchronized (thread-safe) sorted map backed by the specified sorted map.
static  SortedSet	synchronizedSortedSet(SortedSet s) Returns a synchronized (thread-safe) sorted set backed by the specified sorted set.
static  Collection	unmodifiableCollection(Collection c) Returns an unmodifiable view of the specified collection.
static  List	unmodifiableList(List list) Returns an unmodifiable view of the specified list.
static  Map	unmodifiableMap(Map m) Returns an unmodifiable view of the specified map.
static  Set	unmodifiableSet(Set s) Returns an unmodifiable view of the specified set.
static  SortedMap	unmodifiableSortedMap(SortedMap m) Returns an unmodifiable view of the specified sorted map.
static  SortedSet	unmodifiableSortedSet(SortedSet s) Returns an unmodifiable view of the specified sorted set.