Java Study Notes 33 (Collection framework 7: Collections tool class ),

Java Study Notes 33 (Collection framework 7: Collections tool class ),

The array has a tool class and operations on the array.

The collection also has a tool class: Collections

Examples of common methods:

Package demo; import java. util. arrayList; import java. util. collections; import java. util. list; public class CollectionDemo {public static void main (String [] args) {function1 (); function2 (); function3 ();} public static void function1 () {// sort sorting: it must be a List set, sorted in ascending order // String, in alphabetical order List <String> list = new ArrayList <String> (); list. add ("a"); list. add ("d"); list. add ("s"); list. add ("g"); Collections. sort (list); System. out. println (list); // [a, d, g, s]} public static void function2 () {// binary search, note that the list set must be a List set. // the prerequisite for semi-query is to complete the sorting list <Integer> list = new ArrayList <Integer> (); list. add (11); list. add (3); list. add (16); list. add (9); list. add (15); Collections. sort (list); System. out. println (list); // [3, 9, 11, 15, 16] int index = Collections. binarySearch (list, 11); System. out. println (index); // 2 // The element with index 2 is 11} public static void function3 () {// List <Integer> list = new ArrayList <Integer> (); for (Integer I = 1; I <10; I ++) {list. add (I);} System. out. println (list); // [1, 2, 3, 4, 5, 6, 7, 8, 9] Collections. reverse (list); // flip collection System. out. println (list); // [9, 8, 7, 6, 5, 4, 3, 2, 1] Collections. shuffle (list); // randomly arrange System. out. println (list); // [7, 3, 4, 5, 8, 2, 6, 9, 1] // The output is different each time }}