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：

     public static void main(String[] args) {

         List<Integer> nums = new ArrayList<Integer>();

         nums.add(2);

         nums.add(9);

         nums.add(7);

         nums.add(1);

         nums.add(0);

         System.out.println(nums);

         Collections.sort(nums);

         System.out.println(nums);

     }

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：

 import java.util.Date;

 public class Record implements Comparable<Record> {

     private String name;

     private int age;

     private Date start;

     public Record(String name, int age, Date start) {

         this.name = name;

         this.age = age;

         this.start = start;

     }

     public String getName() {

         return name;

     }

     public void setName(String name) {

         this.name = name;

     }

     public int getAge() {

         return age;

     }

     public void setAge(int age) {

         this.age = age;

     }

     public Date getStart() {

         return start;

     }

     public void setStart(Date start) {

         this.start = start;

     }

     @Override

     public int compareTo(Record o) {

         int nameIndex = this.name.compareTo(o.name);

         int ageIndex = 0;

         int startIndex = 0;

         // 姓名一样则比较年龄

         if (nameIndex == 0) {

             ageIndex = this.age - o.age;

         }

         // 年龄一样则比较开始时间

         if (ageIndex == 0) {

             boolean isAfter = this.start.after(o.start);

             if (isAfter) {

                 startIndex = 1;

             } else {

                 startIndex = -1;

             }

         }

         return nameIndex+ageIndex+startIndex;

     }

 }

No2.稍复杂一些的排序：

 import java.text.ParseException;

 import java.text.SimpleDateFormat;

 import java.util.ArrayList;

 import java.util.Collections;

 import java.util.List;

 public class ListOrder {

     public static void main(String[] args) throws ParseException {

         SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");

         List<Record> records = new ArrayList<Record>();

         records.add(new Record("a", 2, df.parse("2015-12-16")));

         records.add(new Record("d", 8, df.parse("2015-12-16")));

         records.add(new Record("a", 1, df.parse("2019-12-16")));

         records.add(new Record("x", 0, df.parse("2014-12-16")));

         records.add(new Record("a", 1, df.parse("2018-12-16")));

         for (Record record : records) {

             System.out.println("name :" + record.getName() + " age :" + record.getAge() + " start :" + record.getStart());

         }

         Collections.sort(records);

         System.out.println("--------------------------------------");

         for (Record record : records) {

             System.out.println("name :" + record.getName() + " age :" + record.getAge() + " start :" + record.getStart());

         }

     }

 }

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：

 import java.util.Date;

 public class Record {

     private String name;

     private int age;

     private Date start;

     public Record(String name, int age, Date start) {

         this.name = name;

         this.age = age;

         this.start = start;

     }

     public String getName() {

         return name;

     }

     public void setName(String name) {

         this.name = name;

     }

     public int getAge() {

         return age;

     }

     public void setAge(int age) {

         this.age = age;

     }

     public Date getStart() {

         return start;

     }

     public void setStart(Date start) {

         this.start = start;

     }

 }

No3:代码：

 import java.text.ParseException;

 import java.text.SimpleDateFormat;

 import java.util.ArrayList;

 import java.util.Collections;

 import java.util.Comparator;

 import java.util.List;

 public class ListOrder {

     public static void main(String[] args) throws ParseException {

         SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");

         List<Record> records = new ArrayList<Record>();

         records.add(new Record("a", 2, df.parse("2015-12-16")));

         records.add(new Record("d", 8, df.parse("2015-12-16")));

         records.add(new Record("a", 1, df.parse("2019-12-16")));

         records.add(new Record("x", 0, df.parse("2014-12-16")));

         records.add(new Record("a", 1, df.parse("2018-12-16")));

         for (Record record : records) {

             System.out

                     .println("name :" + record.getName() + " age :" + record.getAge() + " start :" + record.getStart());

         }

         Collections.sort(records, new Comparator<Record>() {

             @Override

             public int compare(Record r1, Record r2) {

                 int nameIndex = r1.getName().compareTo(r2.getName());

                 int ageIndex = 0;

                 int startIndex = 0;

                 // 姓名一样则比较年龄

                 if (nameIndex == 0) {

                     ageIndex = r1.getAge() - r2.getAge();

                 }

                 // 年龄一样则比较开始时间

                 if (ageIndex == 0) {

                     boolean isAfter = r1.getStart().after(r2.getStart());

                     if (isAfter) {

                         startIndex = 1;

                     } else {

                         startIndex = -1;

                     }

                 }

                 return nameIndex + ageIndex + startIndex;

             }

         });

         System.out.println("--------------------------------------");

         for (Record record : records) {

             System.out

                     .println("name :" + record.getName() + " age :" + record.getAge() + " start :" + record.getStart());

         }

     }

 }

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

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

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

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