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

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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]

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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;
     }

 }

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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

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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

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reference:

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

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

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