JAVA对ArrayList排序

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java如何对ArrayList中对象按照该对象某属性排序

增加排序功能，打印时：输出学生对象的时候，需要先按照年龄排序，如果年龄相同，则按照姓名排序，如果姓名也相同，则按照学号排序。

import java.util.ArrayList;import java.util.Collections;import java.util.Comparator;public class ComparableTest { public static void main(String[] args) {  Comparator<Student> comparator = new Comparator<Student>(){   public int compare(Student s1, Student s2) {    //先排年龄    if(s1.age!=s2.age){     return s1.age-s2.age;    }    else{     //年龄相同则按姓名排序     if(!s1.name.equals(s2.name)){      return s1.name.compareTo(s2.name);     }     else{      //姓名也相同则按学号排序      return s1.id-s2.id;     }    }   }  };  Student stu1 = new Student (1,"zhangsan","male",28,"cs");  Student stu2 = new Student (2,"lisi","female",19,"cs");  Student stu3 = new Student (3,"wangwu","male",22,"cs");  Student stu4 = new Student (4,"zhaoliu","female",17,"cs");  Student stu5 = new Student (5,"jiaoming","male",22,"cs");  ArrayList<Student> List = new ArrayList<Student>();  List.add(stu1);  List.add(stu2);  List.add(stu3);  List.add(stu4);  List.add(stu5);   //这里就会自动根据规则进行排序  Collections.sort(List,comparator);  display(List); }  static void display(ArrayList<Student> lst){  for(Student s:lst)   System.out.println(s); }}class Student{ int age; int id; String gender; String name; String cs; Student(int id,String name,String gender,int age,String cs){  this.age=age;  this.name=name;  this.gender=gender;  this.id=id;  this.cs=cs; } public String toString(){  return id+"  "+name+"  "+gender+"  "+age+"  "+cs; }}

以一个point点类做例子：

import java.util.*;     public class Test {     public static void main(String[] args){     List<Point> points=new ArrayList<Point>();          Point point1=new Point();     point1.setX(1324);     point1.setY(345);     point1.setZ(436);     points.add(point1);          Point point2=new Point();     point2.setX(23);     point2.setY(8941.656);     point2.setZ(431412);     points.add(point2);          Point point3=new Point();     point3.setX(786584);     point3.setY(23452);     point3.setZ(43563);     points.add(point3);          //根据X排序     Collections.sort(points,new SortByX());          for(Point p:points){      System.out.print(p.getX()+"\t"+p.getY()+"\t"+p.getZ());      System.out.println();     }          //根据Y排序   //  Collections.sort(points,new SortByY());   //     //  for(Point p:points){   //   System.out.print(p.getX()+"\t"+p.getY()+"\t"+p.getZ());   //   System.out.println();   //  }   //     //  //根据Z排序   //  Collections.sort(points,new SortByZ());   //     //  for(Point p:points){   //   System.out.print(p.getX()+"\t"+p.getY()+"\t"+p.getZ());   //   System.out.println();   //  }   }     }     class Point{   private double x;   private double y;   private double z;   public double getX() {     return x;   }   public void setX(double x) {     this.x = x;   }   public double getY() {     return y;   }   public void setY(double y) {     this.y = y;   }   public double getZ() {     return z;   }   public void setZ(double z) {     this.z = z;   }   public Point(){}   }     //根据X排序   class SortByX implements Comparator{   public int compare(Object obj1,Object obj2){     Point point1=(Point)obj1;     Point point2=(Point)obj2;     if(point1.getX()>point2.getX())      return 1;     else     return 0;   }   }   //根据Y排序   class SortByY implements Comparator{   public int compare(Object obj1,Object obj2){     Point point1=(Point)obj1;     Point point2=(Point)obj2;     if(point1.getY()>point2.getY())      return 1;     else     return 0;   }   }   //根据Z排序   class SortByZ implements Comparator{   public int compare(Object obj1,Object obj2){     Point point1=(Point)obj1;     Point point2=(Point)obj2;     if(point1.getZ()>point2.getZ())      return 1;     else     return 0;   }   }

//一个POJO例子class User { String name; String age;  public User(String name,String age){  this.name=name;  this.age=age; } public String getAge() {  return age; } public void setAge(String age) {  this.age = age; } public String getName() {  return name; } public void setName(String name) {  this.name = name; } }//具体的比较类，实现Comparator接口import java.util.Comparator;import java.util.List;import java.util.ArrayList;import java.util.Collections;public class ComparatorUser implements Comparator{ public int compare(Object arg0, Object arg1) {  User user0=(User)arg0;  User user1=(User)arg1;   //首先比较年龄，如果年龄相同，则比较名字  int flag=user0.getAge().compareTo(user1.getAge());  if(flag==0){   return user0.getName().compareTo(user1.getName());  }else{   return flag;  }   } }//测试类public class SortTest {  public static void main(String[] args){  List userlist=new ArrayList();  userlist.add(new User("dd","4"));  userlist.add(new User("aa","1"));  userlist.add(new User("ee","5"));  userlist.add(new User("bb","2"));    userlist.add(new User("ff","5"));  userlist.add(new User("cc","3"));  userlist.add(new User("gg","6"));    ComparatorUser comparator=new ComparatorUser();  Collections.sort(userlist, comparator);     for (int i=0;i<userlist.size();i++){   User user_temp=(User)userlist.get(i);      System.out.println(user_temp.getAge()+","+user_temp.getName());   }   }} //首先年龄排序，如果年龄相同，则按名字排序

结果:    1, aa    2, bb    3, cc    4, dd    5, ee                    //注意:同样是5岁的人，则比较名字(ee,ff)，然后排序   5, ff    6, gg

最后这个没有用java的Comparable接口，自己写的排序函数。
要用JAVA写个东西读取TXT中的数据 且要计算出平均值和总值 最后还要按总值排序。  TXT的文件如下：学号 姓名   语文 数学 英语 平均值 总值  排序1   李守东   83  73  752   徐贤坤   58  58  873   钱云宋   41  86  904   陈平     83  43  655   金荣权   93  88  636   陈如棉   99  93  437   章可可   98  62  728   陈伟奔   87  43  769   张如祥   69  58  7810  丁尚游   80  56  5711  林宏旦   91  90  7612  曾上腾   100 96  5413  谢作品   82  100 5514  温从卫   73  46  10115  李明察   81  41  7516  彭鸿威   46  46  8917  翁文秀   57  43  5818  陈家伟   63  58  9819  温正考   100 64  5720  周文湘   50  50  7921  吴杰     65  65  8322  赖登城   60  79  5323  聂树露   51  76  4524  张雅琴   68  95  5625  曾瑞约   88  63  5826  王志强   96  79  7827  徐贤所   66  46  7428  陈祥枭   82  96  9129  温婷婷   41  73  9630  应孔余   66  81  7131  宋成取   71  68  6232  黄益省   65  56  4333  陈思文   55  100 4434  上官福新 64  62  7035  钟国横   49  69  5636  林型涨   78  73  50 
import java.io.BufferedReader;import java.io.File;import java.io.FileNotFoundException;import java.io.FileReader;import java.io.IOException;import java.io.PrintWriter;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;public class Testa { public static void main(String[] args)  {  //传入参数为文件目录  test("d:/a.txt"); }  public static void test(String filePath){  BufferedReader br = null;  try {   br = new BufferedReader(new FileReader(filePath));  } catch (FileNotFoundException e) {   e.printStackTrace();   return;  }    String []columnName = {"Id", "Name", "Languages", "Math", "English"}; //列名  int []courseIndexs = {2, 3, 4};          //课程对应的列  int i,j,index;  String line;  List<Map<String, Object>> students = new ArrayList<Map<String, Object>>();  //记录Id和总值,用于排序  List<Map<String, Object>> sortList = new ArrayList<Map<String, Object>>();  try {   br.readLine(); //去掉第一行   while((line = br.readLine()) != null){    index = 0;    String []se = line.split(" ");    Map<String, Object> student = new HashMap<String, Object>();    for(i = 0; i < se.length; i++){     if("".equals(se[i])){      continue;     }     if(index >= columnName.length){      continue;     }     student.put(columnName[index], se[i]);     index++;    }    //计算平均值,总值    double total = 0;    for(j = 0; j < courseIndexs.length; j++){     total += Double.parseDouble((String) student.get(columnName[courseIndexs[j]]));    }    double average = total / courseIndexs.length;    //只取一位小数    average = Math.round(average * 10)/10;    student.put("Total", total);    student.put("Average", average);        Map<String, Object> sort = new HashMap<String, Object>();    sort.put("Id", student.get("Id"));    sort.put("Total", student.get("Total"));    sortList.add(sort);        students.add(student);   }   br.close();      //选择排序   for(i = 0; i < sortList.size(); i++){    for(j = i + 1; j < sortList.size(); j++){     if((Double)sortList.get(i).get("Total") < (Double)sortList.get(j).get("Total")){      Map<String, Object> temp = sortList.get(i);      sortList.set(i, sortList.get(j));      sortList.set(j, temp);     }    }   }   Map<Object, Integer> sortedId = new HashMap<Object, Integer>();   for(i = 0; i < sortList.size(); i++){    sortedId.put(sortList.get(i).get("Id"), i+1);   }      //设定序号   for(j = 0; j < students.size(); j++){    students.get(j).put("Order", sortedId.get(students.get(j).get("Id")));   }      //输出(写到原文件)   //PrintWriter pw = new PrintWriter(new File(filePath));   //输出(写到其他文件)   PrintWriter pw = new PrintWriter(new File("D:/b.txt"));      pw.println("Id\tName\tLan\tMath\tEnglish\tAverage\tTotal\tSort");   int cIndex;   for(i = 0; i < students.size(); i++){    Map<String, Object> st = students.get(i);    cIndex = 0;    pw.println(st.get(columnName[cIndex++]) + "\t" + st.get(columnName[cIndex++])      + "\t" + st.get(columnName[cIndex++])+ "\t" + st.get(columnName[cIndex++])      + "\t" + st.get(columnName[cIndex++])      + "\t" + st.get("Total")      + "\t" + st.get("Average")      + "\t" + st.get("Order"));   }   pw.flush();   pw.close();  } catch (IOException e) {   e.printStackTrace();  } }}

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