Question

I am getting student information from database,

ArrayList<Student> studentList = session.createQuery("from Student order by Date").list();

the studentList contains name , id ,marks, by date. I want to display this arraylist by name, becase the same student name contains different date.
How to sort this from arraylist.
Ex studentList value is

1 x  2010-10-01
2 y  2010-10-05
3 z  2010-10-15
1 x  2010-10-10
1 x  2010-10-17
2 y  2010-10-15
4 xx 2010-10-10

I want to display this to

1 x  2010-10-01
1 x  2010-10-10
1 x  2010-10-17
2 y  2010-10-05
2 y  2010-10-15
3 z  2010-10-15
4 xx 2010-10-10

and store this to another array list

Answer 1

There are plenty of questions to look at that answer this, such as:
https://stackoverflow.com/questions/2784514/sort-arraylist-of-custom-objects-by-property

But here is an example program of what to do. I assumed you wanted to sort by name first, and then date. You can put logic to do that in the custom comparator.

import java.util.*;

public class SortExample {

  public static class Student {
    public String name;
    public String date;

    public Student(String name, String date) {
      this.name = name;
      this.date = date;
    }
  }

  public static class StudentComparator implements Comparator<Student> {
      @Override
      public int compare(Student s, Student t) {
         int f = s.name.compareTo(t.name);
         return (f != 0) ? f : s.date.compareTo(t.date);
      }
  }

  public static void main(String args[]) {
    ArrayList<Student> l = new ArrayList<Student>(Arrays.asList(
      new Student ("x","2010-10-5"),
      new Student ("z","2010-10-15"),
      new Student ("y","2010-10-05"),
      new Student ("x","2010-10-1")
    ));

    System.out.println("Unsorted");
    for(Student s : l) {
      System.out.println(s.name + " " + s.date);
    }

    Collections.sort(l, new StudentComparator());

    System.out.println("Sorted");
    for(Student s : l) {
      System.out.println(s.name + " " + s.date);
    }
  }
}

Output of this is:

Unsorted
x 2010-10-5
z 2010-10-15
y 2010-10-05
x 2010-10-1
Sorted
x 2010-10-1
x 2010-10-5
y 2010-10-05
z 2010-10-15

EDIT: This sorts the array list in place. You’d have to copy it first if you want it as a new list.