Java has learned twenty-four (collection tool class Collections) from scratch, and tool class collections

Source: Internet
Author: User
Tags comparable

Java has learned twenty-four (collection tool class Collections) from scratch, and tool class collections
I. Collections introduction in Application Development of Collections, several interfaces and several subclasses of a set are the most commonly used. However, in JDK, a tool class for collection operations is provided-Collections, you can directly use this convenient operation set 2. Common methods and constants of the Collections class

No. Method Type Description
1 Public static final List EMPTY_LIST Constant Returns an empty List set.
2 Public static final Set EMPTY_SET Constant Returns an empty Set.
3 Public static final Map EMPTY_MAP Constant Returns an empty Map set.
4 Public static <T> boolean addAll (Collection <? Super T> c, T...) Normal Add content to a set
5 Public static <T extends Object & Comparable <? Super T> T max (Collection <? Extends T> coll) Normal Find the maximum content, sort by comparator, and return the maximum element of the given set in the natural order of the elements
6 Public static <T extends Object & Comparable <? Super T> T min (Collection <? Extends T> coll) Normal Find the minimum content in the set and return the minimum elements of the given set in the natural order of the elements by the comparator.
7 Public static <T> boolean replaceAll (List <T> list, T oldVal, T newVal) Normal Replace the specified content of the set with a new value to replace all the specified values in the set with another value.
8 Public static void reverse (List <?> List) Normal Reverses the order of elements in a specified List set.
9 Public static <T> int binarySearch (List <? Extends Comparable <? Super T> list, T key) Normal Find the specified content in the Set

Use the binary search algorithm to find the specified List set to obtain
Determines the index location of an object.

10 Public static final <T> List <T> emptyList () Normal Returns an empty List set.
11 Public static final <K, V> Map <K, V> emptyMap () Normal Returns an empty Map set.
12 Public static final <T> Set <T> emptySet () Normal Returns an empty Set.
13 Public static <T extends Comparable <? Super T> void sort (List <T> list) Normal Sort the set by the Comparable interface.

Based on the natural order of elements
Sort.

14 Public static void swap (List <?> List, int I, int j) Normal Swap elements at a specified position
3. Reverse the element order in the specified List set
Package com. pb. demo2; import java. util. collections; import java. util. using list; import java. util. list; public class CollectionsTest1 {public static void main (String [] args) {// declare the set and add the element 'LIST' <String> list = new struct list <String> (); List. add ("one"); list. add ("two"); list. add ("three"); System. out. println ("======= normal traversal =============="); for (String s: list) {System. out. print (s + "\ t");} System. out. println (); System. out. println ("======= execute the reverse method =============="); Collections. reverse (list); for (String s: list) {System. out. print (s + "\ t ");}}}
4. The sort method is used to sort the specified List set in ascending order.
Package com. pb. demo2; import java. util. arrayList; import java. util. collections; import java. util. list; public class CollectionsTest2 {public static void main (String [] args) {// declare the set and add the set List <Integer> list = new ArrayList <Integer> (); list. add (7); list. add (2); list. add (5); list. add (3); list. add (1); System. out. println ("======= normal traversal =============="); for (Integer I: list) {System. out. print (I + "\ t");} System. out. println ("\ n ======= execute the sort method ============="); Collections. sort (list); for (Integer I: list) {System. out. print (I + "\ t");} System. out. println ("\ n ======= execute the reverse method =============="); Collections. reverse (list); for (Integer I: list) {System. out. print (I + "\ t ");}}}

Result:

========= Normal traversal ================= 7 2 5 3 1 ======= execute the sort method ==== ========= 1 2 3 5 7 ======= execute the reverse method =================== 7 5 3 2 1
5. Set search and Replacement Methods
Package com. pb. demo2; import java. util. arrayList; import java. util. collections; import java. util. list; public class CollectionsTest3 {public static void main (String [] args) {// declare the set and add the set. // create the set List <String> list = new ArrayList <String> (); // Add 10 different word lists. add ("this"); list. add ("is"); list. add ("collection"); list. add ("test"); list. add ("and"); list. add ("we"); list. add ("can"); list. add ("learn"); list. add ("how"); list. add ("to"); System. out. println ("======= normal traversal =============="); for (String s: list) {System. out. print (s + "\ t");} // print the maximum and minimum elements in the output set System. out. println ("\ n ========= print the maximum and minimum elements in the output set ========="); String max = Collections. max (list); String min = Collections. min (list); System. out. println ("maximum value in the list set:" + max); System. out. println ("minimum value in the list set:" + min); System. out. println ("\ n ======= execute the sort method ============="); Collections. sort (list); for (String s: list) {System. out. print (s + "\ t");} // binarySearch can be used only when sorting is required. out. println ("\ n =============== binarySearch search index by content =========================" ); system. out. println ("we index in the list is:" + Collections. binarySearch (list, "we"); System. out. println ("=============== replaceAll method ======================== "); // replaceAll Collections. replaceAll (list, "we", "our"); for (String s: list) {System. out. print (s + "\ t");} // swap System. out. println ("====== swap ======"); Collections. swap (list, 0, 9); for (String s: list) {System. out. print (s + "\ t ");}}}

Result:

========= Normal traversal ================= this is collection test and we can learn how to =========== print maximum and minimum elements in the output set ======== maximum values in the list set: minimum value in the welist set: and ======= execute the sort method ============== and can collection how is learn test this to we ========== ======= binarySearch search index by content ====================== the index in the list of we is: 9 =============== replaceAll method ========================== and can collection how is learn test this to our ====== swap ====== our can collection how is learn test this to and
6. Use Arrays. asList to generate a set
Package com. pb. demo2; import java. util. arrays; import java. util. list; public class Test1 {public static void main (String [] args) {String str = "a, B, c, d, e, f "; list <String> list1 = Arrays. asList (str); System. out. println ("length of list1:" + list1.size (); for (String s: list1) {System. out. print (s + "\ t");} System. out. println ("\ n is separated by commas to generate a set"); List <String> list2 = Arrays. asList (str. split (","); System. out. println ("length of list2:" + list2.size (); for (String s: list2) {System. out. print (s + "\ t ");}}}

Result:

List1 length: 1a, B, c, d, e, f separated by commas (,), the length of list2 is generated: 6a B c d e f

 

Related Article

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.