Java集合算法
集合框架定義了可以被應用到集合和映射的幾種算法。
這些算法被定義為集合類中的靜態方法。有幾個方法可以拋出ClassCastException,當它試圖比較不兼容的類型時,或者一個UnsupportedOperationException,當它試圖修改一個不可修改的集合發生。
在集合框架的算法定義的方法總結如下表:
SN | 方法及描述 |
---|---|
1 |
static int binarySearch(List list, Object value, Comparator c) Searches for value in list ordered according to c. Returns the position of value in list, or -1 if value is not found |
2 |
static int binarySearch(List list, Object value) Searches for value in list. The list must be sorted. Returns the position of value in list, or -1 if value is not found. |
3 |
static void copy(List list1, List list2) Copies the elements of list2 to list1. |
4 |
static Enumeration enumeration(Collection c) Returns an enumeration over c. |
5 |
static void fill(List list, Object obj) Assigns obj to each element of list. |
6 |
static int indexOfSubList(List list, List subList) Searches list for the first occurrence of subList. Returns the index of the first match, or .1 if no match is found. |
7 |
static int lastIndexOfSubList(List list, List subList) Searches list for the last occurrence of subList. Returns the index of the last match, or .1 if no match is found. |
8 |
static ArrayList list(Enumeration enum) Returns an ArrayList that contains the elements of enum. |
9 |
static Object max(Collection c, Comparator comp) Returns the maximum element in c as determined by comp. |
10 |
static Object max(Collection c) Returns the maximum element in c as determined by natural ordering. The collection need not be sorted. |
11 |
static Object min(Collection c, Comparator comp) Returns the minimum element in c as determined by comp. The collection need not be sorted. |
12 |
static Object min(Collection c) Returns the minimum element in c as determined by natural ordering. |
13 |
static List nCopies(int num, Object obj) Returns num copies of obj contained in an immutable list. num must be greater than or equal to zero. |
14 |
static boolean replaceAll(List list, Object old, Object new) Replaces all occurrences of old with new in list. Returns true if at least one replacement occurred. Returns false, otherwise. |
15 |
static void reverse(List list) Reverses the sequence in list. |
16 |
static Comparator reverseOrder( ) Returns a reverse comparator |
17 |
static void rotate(List list, int n) Rotates list by n places to the right. To rotate left, use a negative value for n. |
18 |
static void shuffle(List list, Random r) Shuffles (i.e., randomizes) the elements in list by using r as a source of random numbers. |
19 |
static void shuffle(List list) Shuffles (i.e., randomizes) the elements in list. |
20 |
static Set singleton(Object obj) Returns obj as an immutable set. This is an easy way to convert a single object into a set. |
21 |
static List singletonList(Object obj) Returns obj as an immutable list. This is an easy way to convert a single object into a list. |
22 |
static Map singletonMap(Object k, Object v) Returns the key/value pair k/v as an immutable map. This is an easy way to convert a single key/value pair into a map. |
23 |
static void sort(List list, Comparator comp) Sorts the elements of list as determined by comp. |
24 |
static void sort(List list) Sorts the elements of list as determined by their natural ordering. |
25 |
static void swap(List list, int idx1, int idx2) Exchanges the elements in list at the indices specified by idx1 and idx2. |
26 |
static Collection synchronizedCollection(Collection c) Returns a thread-safe collection backed by c. |
27 |
static List synchronizedList(List list) Returns a thread-safe list backed by list. |
28 |
static Map synchronizedMap(Map m) Returns a thread-safe map backed by m. |
29 |
static Set synchronizedSet(Set s) Returns a thread-safe set backed by s. |
30 |
static SortedMap synchronizedSortedMap(SortedMap sm) Returns a thread-safe sorted set backed by sm. |
31 |
static SortedSet synchronizedSortedSet(SortedSet ss) Returns a thread-safe set backed by ss. |
32 |
static Collection unmodifiableCollection(Collection c) Returns an unmodifiable collection backed by c. |
33 |
static List unmodifiableList(List list) Returns an unmodifiable list backed by list. |
34 |
static Map unmodifiableMap(Map m) Returns an unmodifiable map backed by m. |
35 |
static Set unmodifiableSet(Set s) Returns an unmodifiable set backed by s. |
36 |
static SortedMap unmodifiableSortedMap(SortedMap sm) Returns an unmodifiable sorted map backed by sm. |
37 |
static SortedSet unmodifiableSortedSet(SortedSet ss) Returns an unmodifiable sorted set backed by ss. |
例子:
以下是示例,其中演示各種算法。
import java.util.*; public class AlgorithmsDemo { public static void main(String args[]) { // Create and initialize linked list LinkedList ll = new LinkedList(); ll.add(new Integer(-8)); ll.add(new Integer(20)); ll.add(new Integer(-20)); ll.add(new Integer(8)); // Create a reverse order comparator Comparator r = Collections.reverseOrder(); // Sort list by using the comparator Collections.sort(ll, r); // Get iterator Iterator li = ll.iterator(); System.out.print("List sorted in reverse: "); while(li.hasNext()){ System.out.print(li.next() + " "); } System.out.println(); Collections.shuffle(ll); // display randomized list li = ll.iterator(); System.out.print("List shuffled: "); while(li.hasNext()){ System.out.print(li.next() + " "); } System.out.println(); System.out.println("Minimum: " + Collections.min(ll)); System.out.println("Maximum: " + Collections.max(ll)); } }
這將產生以下結果:
List sorted in reverse: 20 8 -8 -20 List shuffled: 20 -20 8 -8 Minimum: -20 Maximum: 20