用Java对地图排序 [英] Sorting a map in java

问题描述

我有一个带有以下键值对组合的树形图

I have a tree map with a following key value pair combination

地图声明如下

Map<String, List<Bean>> outputMap = new TreeMap<String,List<Bean>>();

对应的代码将是

for (String course_date : shiftSet) {
        Bean courseBean = null; 
        boolean  valueExists = false;

                for (Entry<String, List<Bean>> entry: courseMap.entrySet()){
                    valueExists = false;
                    String studentDetail = entry.getKey();
                    String [] studentSet =  StringUtils.getArray(studentDetail , ",");
                    String studentId = studentSet[0];
                    String courseId = studentSet[1];

                    for(Bean resultBean : entry.getValue()){

                        if(course_date.equalsIgnoreCase(resultBean.getCourseDate()){
                            valueExists = true;
                        }
                }
                        if(!valueExists ) {
                            courseBean = new Bean();
                            courseBean.setStudent(studentId);
                            courseBean.setCourse(courseId);
                            List<Bean> courseList = entry.getValue();
                            courseList.add(courseBean);
                            outputMap.put(studentId+courseId, courseList);
                         }
            }
        }

最后，需要将OutputMap插入到courseMap

And finally the OutputMap needs to be inserted to courseMap

OutputMap结果将为

OutputMap result will be

{ADV001,STU02=   
  [Bean[course_id=ADV1, student_id=STU1_2,Day=Wed-Night,courseDate=12-Feb-2014],
   Bean[course_id=ADV1, student_id=STU1_2,Day=Tue-Day,courseDate=11-Feb-2014], 
   Bean[course_id=ADV1, student_id=STU1_2,Day=Tue-Night,courseDate=11-Feb-2014], 
   Bean[course_id=ADV1, student_id=STU1_2,Day=Wed-Day,courseDate=12-Feb-2014]] 

所以在这里我需要根据courseDate对outputMap进行排序?请问如何才能实现所需的输出?

So Here i need to sort the outputMap based on courseDate?Kindly help on how the desired output can be achieved ?

先谢谢了.

推荐答案

TreeMap通过元素的键对元素进行排序，如果courseDate是值的一部分，则必须使用TreeSet，例如

A TreeMap sorts the elements by their key, if courseDate is part of the values, you'd have to use a TreeSet, e.g.

import java.util.Set;
import java.util.TreeSet;

public class Example {

    public static void main(String[] args) {
        Set<Dummy> example = new TreeSet<>();

        example.add( new Dummy(7, "first dummy"));
        example.add( new Dummy(2, "second dummy"));
        example.add( new Dummy(3, "third dummy"));

        System.out.println(example);
    }

    static class Dummy implements Comparable<Dummy>{
        int courseDate;
        String name;

        Dummy(int courseDate, String name) {
            this.courseDate = courseDate;
            this.name = name;
        }

        @Override
        public String toString() {
            return String.format("[Dummy courseDate=%s, name=%s]", courseDate, name);
        }

        @Override
        public int compareTo(Dummy o) {
            // here you specify how the TreeSet will order your elements
            return Integer.compare(this.courseDate, o.courseDate);
        }
    }
}

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