java中对List中的元素进行排序
Collections对List集合中的数据进行排序
有时候需要对集合中的元素按照一定的规则进行排序，这就需要用到
Java中提供的对集合进行操作的工具类Collections，其中的sort方法
No1.先看一个简单的例子：
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 }结果如下：
[2, 9, 7, 1, 0]
[0, 1, 2, 7, 9]
建立一个No2代码要用的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 // 姓名一样则比较年龄
44 if (nameIndex == 0) {
45 ageIndex = this.age - o.age;
46 }
47 // 年龄一样则比较开始时间
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.稍复杂一些的排序：
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 }输出结果：
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提供的第二种排序方法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:代码：
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 // 姓名一样则比较年龄
29 if (nameIndex == 0) {
30 ageIndex = r1.getAge() - r2.getAge();
31 }
32 // 年龄一样则比较开始时间
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：
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
reference:
https://blog.csdn.net/veryisjava/article/details/51675036