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使用JAVA进行排序

利用JAVA完成排序

  当我们在进行数据库进行查询的时候,当需要按某个字段来进行排序的时候,可以使用SQL语句来完成排序,可以升序,也可以降序。JAVA中的Collections类也可以完成这种操作,SQL的用法和这种集合工具类的操作,可以用于不同的情况中,至于怎么用,可以根据业务场景来选择,下面我罗列出具体的代码,大家可以参考。

 

1)创建工程名为sort的JAVA工程

创建包结构:技术分享

 

创建User类:

 

 1 package com.sunyard.bean;
 2 
 3 /**
 4  * <p>
 5  *     用户类,实现Comparable接口,并且在实体类中实现需要排序的逻辑代码
 6  * </p>
 7  * @author:774346810@qq.com
 8  * @date:2017-6-25
 9  */
10 public class User implements Comparable<User>{
11     private String id;//编号
12     private String name;//姓名
13     private double salary;//工资
14     private int age;//年龄
15     private String city;//城市
16     
17     public User(){}
18     
19     public User(String id, String name, double salary, int age, String city) {
20         this.id = id;
21         this.name = name;
22         this.salary = salary;
23         this.age = age;
24         this.city = city;
25     }
26 
27     public String getId() {
28         return id;
29     }
30     public void setId(String id) {
31         this.id = id;
32     }
33     public String getName() {
34         return name;
35     }
36     public void setName(String name) {
37         this.name = name;
38     }
39     public double getSalary() {
40         return salary;
41     }
42     public void setSalary(double salary) {
43         this.salary = salary;
44     }
45     public int getAge() {
46         return age;
47     }
48     public void setAge(int age) {
49         this.age = age;
50     }
51     public String getCity() {
52         return city;
53     }
54     public void setCity(String city) {
55         this.city = city;
56     }
57     
58     @Override
59     public String toString() {
60         return "User [id=" + id + ", name=" + name + ", salary=" + salary
61                 + ", age=" + age + ", city=" + city + "]";
62     }
63     @Override
64     public int compareTo(User o) {
65         int result = ((this.getAge() - o.getAge()) * 10);//按照年龄的降序排序
66         //int result = ((o.getAge() - this.getAge()) * 10);//按照年龄的升序排序
67         //int result = o.getName().compareTo(this.getName());//按照英文字典顺序的降序
68         //int result = this.getName().compareTo(o.getName());//按照英文字典顺序的升序
69         return result;
70     }
71     
72 }

 

创建测试类测试:

 1 package com.sunyard.test;
 2 
 3 import java.util.ArrayList;
 4 import java.util.Collections;
 5 import java.util.List;
 6 
 7 import com.sunyard.bean.User;
 8 
 9 public class Test {
10     public static void main(String[] args) {
11         List<User> users = new ArrayList<User>();
12         User user1 = new User("1", "zhangsan", 10000, 29, "hangzhou");
13         User user2 = new User("2", "lisi", 12000, 25, "hangzhou");
14         User user3 = new User("3", "wangwu", 11000, 27, "hangzhou");
15         User user4 = new User("4", "zhaoliu", 11500, 26, "hangzhou");
16         
17         users.add(user1);
18         users.add(user2);
19         users.add(user3);
20         users.add(user4);
21         
22         System.out.println("排序前 -------------------- >>>");
23         for(int i = 0;i < users.size();i++){
24             System.out.println(users.get(i));
25         }
26         
27         Collections.sort(users);
28         
29         System.out.println("排序后 -------------------- >>>");
30         for(int i = 0;i < users.size();i++){
31             System.out.println(users.get(i));
32         }
33     }
34 }

控制台输出:

 1 排序前 -------------------- >>>
 2 User [id=1, name=zhangsan, salary=10000.0, age=29, city=hangzhou]
 3 User [id=2, name=lisi, salary=12000.0, age=25, city=hangzhou]
 4 User [id=3, name=wangwu, salary=11000.0, age=27, city=hangzhou]
 5 User [id=4, name=zhaoliu, salary=11500.0, age=26, city=hangzhou]
 6 排序后 -------------------- >>>
 7 User [id=2, name=lisi, salary=12000.0, age=25, city=hangzhou]
 8 User [id=4, name=zhaoliu, salary=11500.0, age=26, city=hangzhou]
 9 User [id=3, name=wangwu, salary=11000.0, age=27, city=hangzhou]
10 User [id=1, name=zhangsan, salary=10000.0, age=29, city=hangzhou]

第二种方式,实现自定义的比较器:

自定义比较器代码:

 1 package com.sunyard.util;
 2 
 3 import java.util.Comparator;
 4 
 5 import com.sunyard.bean.User;
 6 
 7 /**
 8  * <p>实现自定义比较器</p>
 9  * @author:774346810@qq.com
10  * @date:2017-6-25
11  */
12 public class UserComparator implements Comparator<User>{
13     
14     @Override
15     public int compare(User o1, User o2) {
16         int result = 0;
17         result = ((o1.getAge() - o2.getAge()) * 10);//升序
18         result = ((o2.getAge() - o1.getAge()) * 10);//降序
19         return result;
20     }
21     
22 }

测试类:

 1 package com.sunyard.test;
 2 
 3 import java.util.ArrayList;
 4 import java.util.Collections;
 5 import java.util.List;
 6 
 7 import com.sunyard.bean.User;
 8 import com.sunyard.util.UserComparator;
 9 
10 public class Demo {
11     public static void main(String[] args) {
12         List<User> users = new ArrayList<User>();
13         User user1 = new User("1", "zhangsan", 10000, 29, "hangzhou");
14         User user2 = new User("2", "lisi", 12000, 25, "hangzhou");
15         User user3 = new User("3", "wangwu", 11000, 27, "hangzhou");
16         User user4 = new User("4", "zhaoliu", 11500, 26, "hangzhou");
17         
18         users.add(user1);
19         users.add(user2);
20         users.add(user3);
21         users.add(user4);
22         
23         System.out.println("排序前 -------------------- >>>");
24         for(int i = 0;i < users.size();i++){
25             System.out.println(users.get(i));
26         }
27         
28         UserComparator comparator = new UserComparator();
29         Collections.sort(users, comparator);
30 
31         System.out.println("排序后 -------------------- >>>");
32         for(int i = 0;i < users.size();i++){
33             System.out.println(users.get(i));
34         }
35     }
36 }

控制台输出:

 1 排序前 -------------------- >>>
 2 User [id=1, name=zhangsan, salary=10000.0, age=29, city=hangzhou]
 3 User [id=2, name=lisi, salary=12000.0, age=25, city=hangzhou]
 4 User [id=3, name=wangwu, salary=11000.0, age=27, city=hangzhou]
 5 User [id=4, name=zhaoliu, salary=11500.0, age=26, city=hangzhou]
 6 排序后 -------------------- >>>
 7 User [id=1, name=zhangsan, salary=10000.0, age=29, city=hangzhou]
 8 User [id=3, name=wangwu, salary=11000.0, age=27, city=hangzhou]
 9 User [id=4, name=zhaoliu, salary=11500.0, age=26, city=hangzhou]
10 User [id=2, name=lisi, salary=12000.0, age=25, city=hangzhou]

 

使用JAVA进行排序