如何在Java中使用hashmap和arraylist

Question

我正在使用带有ArrayList的嵌套哈希映射。 我的目的是，例如

当我在地图中添加列表（id，主题，sessionTime）时：

        map.add("11111", "Engineering", "Tue3");
        map.add("11111", "Math", "Wed4");
        map.add("22222", "Engineering", "Wed2");
        map.add("11111", "Engineering", "Thu9");
        map.add("11111", "Physics", "Fri10");
        map.add("22222", "Chemistry", "Wed4");

我希望它们像这样存储在地图中：

11111-工程-Tue3＆Thu9

11111-数学-周三

11111-物理-星期五

22222-工程-Wed2

22222-化学-周三

要么

11111-工程-Tue3＆Thu9 /数学-Wed4 /物理-Fri10

22222-工程-Wed2 /化学-Wed4

到目前为止，我所做的是：

public class test {

    Map<String, arrayList> map;

    public test()
    {
        map = new HashMap<String, arrayList>();
    }

    public Submission add(String staffId, String subject, String sessionTime)
    {

        arrayList t = map.get(staffId);

        if(t == null)
        {
            t = new arrayList();
            map.put(staffId, t);
        }

        return t.Put(subject, new MySubmission(staffId, subject, sessionTime));

    }

    public class arrayList
    {

        List<Submission> list = new ArrayList<Submission>();

        public Submission Put(String subject, MySubmission mySubmission)
        {

            MySubmission submission = new MySubmission();

            submission.setSubject(subject);
            submission.setTime(mySubmission.getTime());

            list.add(submission);

            return submission;
        }
    }
}

我真的对解决挑战感到困惑...我走在正确的轨道上吗？ 另外，我应该如何编写代码以将它们全部打印出来？

谢谢！

Answer 1

我认为您需要的是List.map的Map.ie.，

Map <字符串，Map <字符串，列表<字符串>>>

下面的示例代码：

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

public class Test {
public static void main(String[] args) throws IOException {

    Map<String,Map<String,List<String>>> scheduleMap=new HashMap<>();

    //Adding
    addSchedule(scheduleMap, "1111", "Engineering", "Tue3");
    addSchedule(scheduleMap, "1111", "Engineering", "Wed2");
    addSchedule(scheduleMap, "1111", "Math", "Wed4");
    addSchedule(scheduleMap, "1111", "Physics", "Fri10");
    addSchedule(scheduleMap, "2222", "Engineering", "Wed2");
    addSchedule(scheduleMap, "2222", "Chemistry ", "Wed4");

    //Printing
    printSchedule(scheduleMap);

}

private static void printSchedule(Map<String, Map<String, List<String>>> scheduleMap) {
    //Sample printing
    for(Entry<String, Map<String, List<String>>> staff : scheduleMap.entrySet()) {
        for(Entry<String,List<String>> subject:staff.getValue().entrySet()) {
            StringBuilder sb=new StringBuilder();
            sb.append(staff.getKey()).append(" : ").append(subject.getKey()).append(" : ");
            for(String sessionTime: subject.getValue()) {
                sb.append(sessionTime).append(", ");
            }
            sb.setLength(sb.length()-2);
            System.out.println(sb.toString());
        }
    }
}

public static void addSchedule(Map<String,Map<String,List<String>>> scheduleMap, String id,String subject,String sessionTime) {
    if(!scheduleMap.containsKey(id)) {
        scheduleMap.put(id, new HashMap<String,List<String>>());
    }
    if(!scheduleMap.get(id).containsKey(subject)) {
        scheduleMap.get(id).put(subject, new ArrayList<String>());
    }
    scheduleMap.get(id).get(subject).add(sessionTime);
}
}