1 package cn.itcast.p2.toolclass.collections.demo;
 2 
 3 import java.util.ArrayList;
 4 import java.util.Collections;
 5 import java.util.Comparator;
 6 import java.util.List;
 7 
 8 import cn.itcast.p2.comparator.ComparatorByLength;
 9 
10 public class CollectionsDemo {
11 
12     public static void
 
 main(String[] args) {
13         // TODO Auto-generated method stub
14         /*
15          * Collections：是集合框架的工具類。
16          * 裡面的方法都是靜態的。
17          */
18 //        demo_1();
19         demo_2();
20         
21     }
22     
23     private static void demo_2() {
24         // TODO Auto-generated method stub
 

25         List<String> list = new ArrayList<String>();
26         
27         list.add("abcde");
28         list.add("cba");
29         list.add("aa");
30         list.add("zzz");
31         list.add("cba");
32         list.add("nbaa");
33         //折半要先排序
34         Collections.sort(list);
 
35         System.out.println(list);
36         
37         int index = Collections.binarySearch(list, "aaa");
38         
39         System.out.println("index="+index);
40         
41         //獲取最大值。
42 //        String max = Collections.max(list);//max=zzz
43         String max = Collections.max(list,new ComparatorByLength());
44         System.out.println("max="+max);
45     }

 1 package cn.itcast.p2.comparator;
 2 
 3 import java.util.Comparator;
 4 
 5 public class ComparatorByLength implements Comparator<String> {
 6 
 7     @Override
 8     public int compare(String o1, String o2) {
 9         // TODO Auto-generated method stub
10         int temp = o1.length()-o2.length();
11         
12         return temp==0?o1.compareTo(o2):temp;
13     }
14 
15 }