java集合中对象某属性比较排序Comparable与Comparator

要对集合中的对象的某属性进行排序有两种方式。

a. 一种是要排序对象类实现comparable接口的compareTo方法；然后把对象放入list；然后调用Collections.sort(list);
b. 一种是不对要排序对象类做任何改动，创建Comparator接口的实现类C；然后 把对象放入list；然后调用Collections.sort(list, C);

a.eg

----------------------------------

 1 public class User implements Comparable<User>{
 2     private String name;
 3     private int age;
 4     private int gender;
 5     private String address;
 6
 7     public String getName() {
 8         return name;
 9     }
10
11     public void setName(String name) {
12         this.name = name;
13     }
14
15     public int getAge() {
16         return age;
17     }
18
19     public void setAge(int age) {
20         this.age = age;
21     }
22
23     public int getGender() {
24         return gender;
25     }
26
27     public void setGender(int gender) {
28         this.gender = gender;
29     }
30
31     public String getAddress() {
32         return address;
33     }
34
35     public void setAddress(String address) {
36         this.address = address;
37     }
38
39     public User() {
40         super();
41     }
42
43     public User(String name, int age, int gender, String address) {
44         super();
45         this.name = name;
46         this.age = age;
47         this.gender = gender;
48         this.address = address;
49     }
50
51
52     @Override
53     public int compareTo(User o) {
54         if(o!=null){
55             if(this.getAge()>o.getAge()){
56
57                return 1;
58             }else if(this.getAge()==o.getAge()){
59
60                return 0;
61
62             }
63
64        }
65         return -1;
66     }
67 }

-------------------------------------------main

 1 List<User> ulist = new ArrayList<User>();
 2 ulist.add(new User("wangbo",29,1,"长沙"));
 3 ulist.add(new User("wumei",44,1,"株洲"));
 4 ulist.add(new User("zhangjie",19,1,"岳阳"));
 5 ulist.add(new User("lihua",36,1,"长沙"));
 6 ulist.add(new User("zhangchangzhe",19,1,"衡阳"));
 7
 8 Collections.sort(list);
 9
10 for(User u:ulist){
11             System.out.println(u.getName()+"\t"+u.getAge()+"\t"+u.getAddress());
12 }
13
14  

==============================================

b.eg

--------------------------------

 1 public class User {
 2     private String name;
 3     private int age;
 4     private int gender;
 5     private String address;
 6
 7     public String getName() {
 8         return name;
 9     }
10
11     public void setName(String name) {
12         this.name = name;
13     }
14
15     public int getAge() {
16         return age;
17     }
18
19     public void setAge(int age) {
20         this.age = age;
21     }
22
23     public int getGender() {
24         return gender;
25     }
26
27     public void setGender(int gender) {
28         this.gender = gender;
29     }
30
31     public String getAddress() {
32         return address;
33     }
34
35     public void setAddress(String address) {
36         this.address = address;
37     }
38
39     public User() {
40         super();
41     }
42
43     public User(String name, int age, int gender, String address) {
44         super();
45         this.name = name;
46         this.age = age;
47         this.gender = gender;
48         this.address = address;
49     }
50
51 }
52
53  

------------------------------

 1 import java.util.Comparator;
 2
 3 public class ComparatorImpl implements Comparator<User>{
 4
 5     @Override
 6     public int compare(User o1, User o2) {
 7
 8         if(null!=o1 && null!=o2){
 9             if(o1.getAge() >o2.getAge()){
10                 return 1;
11             }else if(o1.getAge() ==o2.getAge()){
12                 return 0;
13             }
14         }
15         return -1;
16     }
17
18 }

-----------------------------------main

 1 List<User> ulist = new ArrayList<User>();
 2         ulist.add(new User("wangbo",29,1,"长沙"));
 3         ulist.add(new User("wumei",44,1,"株洲"));
 4         ulist.add(new User("zhangjie",19,1,"岳阳"));
 5         ulist.add(new User("lihua",36,1,"长沙"));
 6         ulist.add(new User("zhangchangzhe",19,1,"衡阳"));
 7         Collections.sort(ulist, new ComparatorImpl());
 8         for(User u:ulist){
 9             System.out.println(u.getName()+"\t"+u.getAge()+"\t"+u.getAddress());
10         }