Comparator跟Comparable比较
Comparator和Comparable比较
当需要排序的集合或数组不是单纯的数字型时,通常可以使用Comparator或Comparable,以简单的方式实现对象排序或自定义排序。
一、Comparator
强行对某个对象collection进行整体排序的比较函数,可以将Comparator传递给Collections.sort或Arrays.sort。
接口方法:
1/**
2 * @return o1小于、等于或大于o2,分别返回负整数、零或正整数。
3*/
4int compare(Object o1, Object o2);
2 * @return o1小于、等于或大于o2,分别返回负整数、零或正整数。
3*/
4int compare(Object o1, Object o2);
案例:
1import java.util.Arrays;
2import java.util.Comparator;
3
4publicclass SampleComparator implements Comparator {
5
6publicint compare(Object o1, Object o2) {
7return toInt(o1) - toInt(o2);
8 }
9
10privateint toInt(Object o) {
11 String str = (String) o;
12 str = str.replaceAll("一", "1");
13 str = str.replaceAll("二", "2");
14 str = str.replaceAll("三", "3");
15return Integer.parseInt(str);
16 }
17
18/**
19 * 测试方法
20*/
21publicstaticvoid main(String[] args) {
22 String[] array =new String[] { "一二", "三", "二" };
23 Arrays.sort(array, new SampleComparator());
24for (int i =0; i < array.length; i++) {
25 System.out.println(array[i]);
26 }
27 }
28
29}
2import java.util.Comparator;
3
4publicclass SampleComparator implements Comparator {
5
6publicint compare(Object o1, Object o2) {
7return toInt(o1) - toInt(o2);
8 }
9
10privateint toInt(Object o) {
11 String str = (String) o;
12 str = str.replaceAll("一", "1");
13 str = str.replaceAll("二", "2");
14 str = str.replaceAll("三", "3");
15return Integer.parseInt(str);
16 }
17
18/**
19 * 测试方法
20*/
21publicstaticvoid main(String[] args) {
22 String[] array =new String[] { "一二", "三", "二" };
23 Arrays.sort(array, new SampleComparator());
24for (int i =0; i < array.length; i++) {
25 System.out.println(array[i]);
26 }
27 }
28
29}
二、Comparable
强行对实现它的每个类的对象进行整体排序,实现此接口的对象列表(和数组)可以通过Collections.sort或Arrays.sort进行自动排序。
接口方法:
1/**
2 * @return 该对象小于、等于或大于指定对象o,分别返回负整数、零或正整数。
3*/
4int compareTo(Object o);
2 * @return 该对象小于、等于或大于指定对象o,分别返回负整数、零或正整数。
3*/
4int compareTo(Object o);
假设对象User,需要按年龄排序:
1publicclass User {
2
3private String id;
4privateint age;
5
6public User(String id, int age) {
7this.id = id;
8this.age = age;
9 }
10
11publicint getAge() {
12return age;
13 }
14
15publicvoid setAge(int age) {
16this.age = age;
17 }
18
19public String getId() {
20return id;
21 }
22
23publicvoid setId(String id) {
24this.id = id;
25 }
26
27}
2
3private String id;
4privateint age;
5
6public User(String id, int age) {
7this.id = id;
8this.age = age;
9 }
10
11publicint getAge() {
12return age;
13 }
14
15publicvoid setAge(int age) {
16this.age = age;
17 }
18
19public String getId() {
20return id;
21 }
22
23publicvoid setId(String id) {
24this.id = id;
25 }
26
27}
改造后的对象:
1import java.util.Arrays;
2
3publicclass User implements Comparable {
4
5private String id;
6privateint age;
7
8public User(String id, int age) {
9this.id = id;
10this.age = age;
11 }
12
13publicint getAge() {
14return age;
15 }
16
17publicvoid setAge(int age) {
18this.age = age;
19 }
20
21public String getId() {
22return id;
23 }
24
25publicvoid setId(String id) {
26this.id = id;
27 }
28
29publicint compareTo(Object o) {
30returnthis.age - ((User) o).getAge();
31 }
32
33/**
34 * 测试方法
35*/
36publicstaticvoid main(String[] args) {
37 User[] users =new User[] { new User("a", 30), new User("b", 20) };
38 Arrays.sort(users);
39for (int i =0; i < users.length; i++) {
40 User user = users[i];
41 System.out.println(user.getId() +""+ user.getAge());
42 }
43 }
44
45}
2
3publicclass User implements Comparable {
4
5private String id;
6privateint age;
7
8public User(String id, int age) {
9this.id = id;
10this.age = age;
11 }
12
13publicint getAge() {
14return age;
15 }
16
17publicvoid setAge(int age) {
18this.age = age;
19 }
20
21public String getId() {
22return id;
23 }
24
25publicvoid setId(String id) {
26this.id = id;
27 }
28
29publicint compareTo(Object o) {
30returnthis.age - ((User) o).getAge();
31 }
32
33/**
34 * 测试方法
35*/
36publicstaticvoid main(String[] args) {
37 User[] users =new User[] { new User("a", 30), new User("b", 20) };
38 Arrays.sort(users);
39for (int i =0; i < users.length; i++) {
40 User user = users[i];
41 System.out.println(user.getId() +""+ user.getAge());
42 }
43 }
44
45}
三、Comparator和Comparable的区别
先看一下使用Comparator对User集合实现排序的方式:
1import java.util.Arrays;
2import java.util.Comparator;
3
4publicclass UserComparator implements Comparator {
5
6publicint compare(Object o1, Object o2) {
7return ((User) o1).getAge() - ((User) o2).getAge();
8 }
9
10/**
11 * 测试方法
12*/
13publicstaticvoid main(String[] args) {
14 User[] users =new User[] { new User("a", 30), new User("b", 20) };
15 Arrays.sort(users, new UserComparator());
16for (int i =0; i < users.length; i++) {
17 User user = users[i];
18 System.out.println(user.getId() +""+ user.getAge());
19 }
20 }
21
22}
2import java.util.Comparator;
3
4publicclass UserComparator implements Comparator {
5
6publicint compare(Object o1, Object o2) {
7return ((User) o1).getAge() - ((User) o2).getAge();
8 }
9
10/**
11 * 测试方法
12*/
13publicstaticvoid main(String[] args) {
14 User[] users =new User[] { new User("a", 30), new User("b", 20) };
15 Arrays.sort(users, new UserComparator());
16for (int i =0; i < users.length; i++) {
17 User user = users[i];
18 System.out.println(user.getId() +""+ user.getAge());
19 }
20 }
21
22}
一个类实现了Camparable接口则表明这个类的对象之间是可以相互比较的,这个类对象组成的集合就可以直接使用sort方法排序。
Comparator可以看成一种算法的实现,将算法和数据分离,Comparator也可以在下面两种环境下使用:
1、类的设计师没有考虑到比较问题而没有实现Comparable,可以通过Comparator来实现排序而不必改变对象本身
2、可以使用多种排序标准,比如升序、降序等