java中對List中的元素進行排序

本文轉載自查看原文 2018-07-22 01:00 6081 java基礎/ java

Collections對List集合中的數據進行排序

有時候需要對集合中的元素按照一定的規則進行排序，這就需要用到

Java中提供的對集合進行操作的工具類Collections，其中的sort方法

No1.先看一個簡單的例子：

 1     public static void main(String[] args) {
 2         List<Integer> nums = new ArrayList<Integer>();
 3         nums.add(2);
 4         nums.add(9);
 5         nums.add(7);
 6         nums.add(1);
 7         nums.add(0);
 8         System.out.println(nums);
 9         Collections.sort(nums);
10         System.out.println(nums);
11     }

結果如下：

[2, 9, 7, 1, 0]
[0, 1, 2, 7, 9]

建立一個No2代碼要用的entity，如下：

 1 import java.util.Date;
 2 
 3 public class Record implements Comparable<Record> {
 4     private String name;
 5     private int age;
 6     private Date start;
 7 
 8     public Record(String name, int age, Date start) {
 9         this.name = name;
10         this.age = age;
11         this.start = start;
12     }
13 
14     public String getName() {
15         return name;
16     }
17 
18     public void setName(String name) {
19         this.name = name;
20     }
21 
22     public int getAge() {
23         return age;
24     }
25 
26     public void setAge(int age) {
27         this.age = age;
28     }
29 
30     public Date getStart() {
31         return start;
32     }
33 
34     public void setStart(Date start) {
35         this.start = start;
36     }
37 
38     @Override
39     public int compareTo(Record o) {
40         int nameIndex = this.name.compareTo(o.name);
41         int ageIndex = 0;
42         int startIndex = 0;
43         // 姓名一樣則比較年齡
44         if (nameIndex == 0) {
45             ageIndex = this.age - o.age;
46         }
47         // 年齡一樣則比較開始時間
48         if (ageIndex == 0) {
49             boolean isAfter = this.start.after(o.start);
50             if (isAfter) {
51                 startIndex = 1;
52             } else {
53                 startIndex = -1;
54             }
55         }
56         return nameIndex+ageIndex+startIndex;
57     }
58 
59 }

No2.稍復雜一些的排序：

 1 import java.text.ParseException;
 2 import java.text.SimpleDateFormat;
 3 import java.util.ArrayList;
 4 import java.util.Collections;
 5 import java.util.List;
 6 
 7 public class ListOrder {
 8     public static void main(String[] args) throws ParseException {
 9         SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
10         List<Record> records = new ArrayList<Record>();
11         records.add(new Record("a", 2, df.parse("2015-12-16")));
12         records.add(new Record("d", 8, df.parse("2015-12-16")));
13         records.add(new Record("a", 1, df.parse("2019-12-16")));
14         records.add(new Record("x", 0, df.parse("2014-12-16")));
15         records.add(new Record("a", 1, df.parse("2018-12-16")));
16         for (Record record : records) {
17             System.out.println("name :" + record.getName() + " age :" + record.getAge() + " start :" + record.getStart());
18         }
19         Collections.sort(records);
20         System.out.println("--------------------------------------");
21         for (Record record : records) {
22             System.out.println("name :" + record.getName() + " age :" + record.getAge() + " start :" + record.getStart());
23         }
24     }
25 }

輸出結果：

name :a age :2 start :Wed Dec 16 00:00:00 CST 2015
name :d age :8 start :Wed Dec 16 00:00:00 CST 2015
name :a age :1 start :Mon Dec 16 00:00:00 CST 2019
name :x age :0 start :Tue Dec 16 00:00:00 CST 2014
name :a age :1 start :Sun Dec 16 00:00:00 CST 2018
--------------------------------------
name :a age :1 start :Sun Dec 16 00:00:00 CST 2018
name :a age :1 start :Mon Dec 16 00:00:00 CST 2019
name :a age :2 start :Wed Dec 16 00:00:00 CST 2015
name :d age :8 start :Wed Dec 16 00:00:00 CST 2015
name :x age :0 start :Tue Dec 16 00:00:00 CST 2014

Collections提供的第二種排序方法sort(List<T> list, Comparator<? super T> c)

所使用的entity：

 1 import java.util.Date;
 2 
 3 public class Record {
 4     private String name;
 5     private int age;
 6     private Date start;
 7 
 8     public Record(String name, int age, Date start) {
 9         this.name = name;
10         this.age = age;
11         this.start = start;
12     }
13 
14     public String getName() {
15         return name;
16     }
17 
18     public void setName(String name) {
19         this.name = name;
20     }
21 
22     public int getAge() {
23         return age;
24     }
25 
26     public void setAge(int age) {
27         this.age = age;
28     }
29 
30     public Date getStart() {
31         return start;
32     }
33 
34     public void setStart(Date start) {
35         this.start = start;
36     }
37 }

No3:代碼：

 1 import java.text.ParseException;
 2 import java.text.SimpleDateFormat;
 3 import java.util.ArrayList;
 4 import java.util.Collections;
 5 import java.util.Comparator;
 6 import java.util.List;
 7 
 8 public class ListOrder {
 9 
10     public static void main(String[] args) throws ParseException {
11         SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
12         List<Record> records = new ArrayList<Record>();
13         records.add(new Record("a", 2, df.parse("2015-12-16")));
14         records.add(new Record("d", 8, df.parse("2015-12-16")));
15         records.add(new Record("a", 1, df.parse("2019-12-16")));
16         records.add(new Record("x", 0, df.parse("2014-12-16")));
17         records.add(new Record("a", 1, df.parse("2018-12-16")));
18         for (Record record : records) {
19             System.out
20                     .println("name :" + record.getName() + " age :" + record.getAge() + " start :" + record.getStart());
21         }
22         Collections.sort(records, new Comparator<Record>() {
23             @Override
24             public int compare(Record r1, Record r2) {
25                 int nameIndex = r1.getName().compareTo(r2.getName());
26                 int ageIndex = 0;
27                 int startIndex = 0;
28                 // 姓名一樣則比較年齡
29                 if (nameIndex == 0) {
30                     ageIndex = r1.getAge() - r2.getAge();
31                 }
32                 // 年齡一樣則比較開始時間
33                 if (ageIndex == 0) {
34                     boolean isAfter = r1.getStart().after(r2.getStart());
35                     if (isAfter) {
36                         startIndex = 1;
37                     } else {
38                         startIndex = -1;
39                     }
40                 }
41                 return nameIndex + ageIndex + startIndex;
42             }
43         });
44         System.out.println("--------------------------------------");
45         for (Record record : records) {
46             System.out
47                     .println("name :" + record.getName() + " age :" + record.getAge() + " start :" + record.getStart());
48         }
49     }
50 }

結果：

reference:

https://blog.csdn.net/veryisjava/article/details/51675036

https://www.jb51.net/article/72284.htm

https://blog.csdn.net/u012901117/article/details/76853113

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