How to sort Arraylist inside arraylist java

Question

I have a list inside a list and I am having problem sorting the string timestamp inside the list. Here is the method that retrieves the timestamp in database:

public static List<List<String>> getLogs(){
    sql = new String("SELECT EmpID, ValidDate, GROUP_CONCAT(ValidTime) AS logTime FROM logs WHERE Processed = 0 GROUP BY EmpID, ValidDate");
    List<List<String>> values = new ArrayList<>();
    List<String> id = new ArrayList<>();
    List<String> valDate = new ArrayList<>();
    List<String> logs = new ArrayList<>();

    try{
        stmt = data.createStatement();
        rs = stmt.executeQuery(sql);

        while(rs.next()){
            id.add(rs.getString("EmpID"));
            valDate.add(String.valueOf(rs.getDate("ValidDate")));
            logs.add(rs.getString("logTime"));
        }
    }catch(SQLException ex){
        ex.printStackTrace();
    }
    values.add(id);
    values.add(valDate);
    values.add(logs);

    return values;
}

this is the result:

2017-07-22 17:02:00,11:31:00,12:14:00
2017-07-22 11:54:00,11:01:00,17:01:00
2017-07-22 17:01:00,11:30:00,12:29:00

It's not in order.

This is how I call this method:

for(int i = 0; i < data.getLogs().get(0).size();i++){
 System.out.println(data.getLogs().get(0).get(i)+" "+data.getLogs().get(1).get(i)+" "+data.getLogs().get(2).get(i));
   }

Answer 1

Change your sql to

sql = new String("SELECT EmpID, ValidDate, GROUP_CONCAT(ValidTime) AS logTime 
       FROM logs WHERE Processed = 0 GROUP BY EmpID, ValidDate ORDER BY ValidDate");

Answer 2

I tried the advise of Ab Sin and search on how to sort data in MySQL and found that its possible to insert ORDER BY inside the GROUP_CONCAT so this is my revised sql statement:

SELECT EmpID, 
       ValidDate, 
       GROUP_CONCAT(ValidTime ORDER BY ValidTime ASC) AS logTime 
FROM logs 
WHERE Processed = 0 
GROUP BY EmpID, ValidDate ORDER BY ValidDate ASC

Thanks for those who replied and helped me.