集合之Collections工具类

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package com.Lucky;   import java.util.ArrayList; import java.util.Collections; import java.util.Comparator;   /*      Collections：java。util.Collections      解析：Collections是集合的工具类，拥有许多处理集合操作的方法                 方法：  addAll();            批量添加数据                      shuffle()            打乱数据                      reverse()             反转                      sort()                 排序                      binarySearch()     先排序再二分查找                      swap()                 互换位置                      copy()                  拷贝数据                      fill()                  修改数据                      min/max()             最大值/最小值      */ public class CollectionsDemo {       public static void main(String[] args) {         //创建一个ArrayList集合         ArrayList<String> arrList=new ArrayList<>();              //调用工具类Collections         System.out.println("---------addAll()------------");         Collections.addAll(arrList,"dsg","A","QER","WSQW","AFGHJEF");         System.out.println(arrList);             System.out.println("---------shuffle()------------");         Collections.shuffle(arrList);  //打乱         System.out.println(arrList);               System.out.println("---------reverse()------------");         Collections.reverse(arrList);   //反转         System.out.println(arrList);           System.out.println("---------sort()------------");         Collections.sort(arrList);   //排序         System.out.println(arrList);         Collections.sort(arrList, new Comparator<String>() {  //可以自定义排序【利用比较器排序】             @Override             public int compare(String o1, String o2) {                 return o2.compareTo(o1);             }         });   //排序         System.out.println(arrList);               System.out.println("---------binarySearch()  先排序再二分查找------------");         ArrayList<Integer> list=new ArrayList<>();         ArrayList<Integer> list1=new ArrayList<>();         Collections.addAll(list,1,2,3,8,9,4,6,7);         list.sort(new Comparator<Integer>() {             @Override             public int compare(Integer o1, Integer o2) {                 return o1-o2;             }         });         System.out.println(list);         //二分查找法查询A字符串         System.out.println(Collections.binarySearch(list,6));  //返回指定key的索引           System.out.println("---------swap()  互换位置------------");          Collections.swap(list,1,3);  //互换位置         System.out.println(list);               System.out.println("---------copy()  拷贝数据------------");         /*         前提条件：新的集合长度比原来的集合长度小，方法会报错，因为 IndexOutOfBoundsException 异常【下标越界异常】          */         Collections.addAll(list1,4,5,6,7,8,9,1,2,3,20,30,54);         Collections.copy(list1,list);  //将list的数据拷贝到list1中,相同位置的数据将会被覆盖         System.out.println(list1);             System.out.println("---------fill()  修改数据------------");         Collections.fill(list1,100);  //将list1的数据全部修改成100；         System.out.println(list1);           System.out.println("---------max/min()  最大值与最小值------------");         System.out.println(Collections.min(list));         System.out.println(Collections.max(list));       } }