Sorting Arraylist objects with multiple fields - Please help

[Chinnu55]

Hi,

I have a ArrayList which contains list of employee objects like

Employee object contains name, dept and designation.

ArrayList al --> employee [object1]
|_ James, D1, manager
employee [object2]
|_ Dave, D2, sales manager
employee [object3]
|_ Roger, D1, accounts manager
employee [object4]
|_ Lisa, D3, engineer
employee [object5]
|_ Angela, D2, PM
employee [object6]
|_ Mike, D1, manager

Now, I want to sort them by designation first and then by department.

i.e. first sort by designation

Roger, D1, accounts manager
Lisa, D3, engineer
James, D1, manager
Mike, D1, manager
Angela, D2, PM
Dave, D2, sales manager

then by department,

Roger, D1, accounts manager
James, D1, manager
Mike, D1, manager
Angela, D2, PM
Dave, D2, sales manager
Lisa, D3, engineer

Please let me know how to achieve and code sample will be great help.

Thanks in advance,
Chinnu

[camickr]

You can use

Bean Comparator « Java Tips Weblog

and

Group Comparator « Java Tips Weblog

[sunde887]

You want to write comparators for you Employee class, and pass it into the Collections.sort method.

Comparator (Java Platform SE 6)

[Tolls]

That's actually sorting by department then designation then name.

[Chinnu55]

Thanks for replying...

I wanted to sort the ArrayList twice i.e. first time by designation and again by department. Due to the confusion I removed Name field.

for ex:
Department Designation
D1 accounts manager
D1 director
D1 manager
D3 engineer
D2 PM
D2 sales manager

If you see above structure, Designation is sorted i.e. under D1 all the employees designation is sorted but, Department is not sorted.

Now, we need to sort Department too

Department Designation
D1 accounts manager
D1 director
D1 manager
D2 PM
D2 sales manager
D3 engineer

Now, Department is sorted.

I was thinking to add 2 inner classes that implements Comparator

    class DesignationComparator implements Comparator {  
	    public int compare(Object o1,Object o2) {  
	    	String strObj1 = ((EmployeeDataBean)o1).getEmployeeDesignation();
			String strObj2 = ((EmployeeDataBean)o2).getEmployeeDesignation();
			return strObj1.toUpperCase().compareTo(strObj2.toUpperCase());
		 }
	}
	
	class DepartmentComparator implements Comparator {  
	    public int compare(Object o1,Object o2) {  
	    	String strObj1 = ((EmployeeDataBean)o1).getEmployeeDepartment();
			String strObj2 = ((EmployeeDataBean)o2).getEmployeeDepartment();
			return strObj1.toUpperCase().compareTo(strObj2.toUpperCase());
		 }
	}

call by

    Collections.sort(empModels, new DesignationComparator());
    Collections.sort(empModels, new DepartmentComparator ());

Please let me know how to achieve with better approach and I am currently using JDK1.4.

Thanks,
Chinnu

[sunde887]

Why are you using such an outdated JDK? That approach looks fine though.

[Tolls]

That is a single sort though.
In SQL terms, ORDER BY department, designation.
In Java it would be a single comparator.
Pseudo:

If thisDepartment == thatDepartment then
    if thisDesignation < thatDesignation then return -1
    else if thisDesignation > thatDesingation then return 1
    else return 0
else if thisDepartment < thatDepartment then return -1
else return 1

I might have my 1's and -1's back to front, but tha's the idea.
Running two Comparators across a single collection like you are trying smacks as unecessary work.

[camickr]

I wanted to sort the ArrayList twice

Why?

I showed you how to do it in one step which is more efficient than doing it twice.

[JosAH]

    Collections.sort(empModels, new DesignationComparator());
    Collections.sort(empModels, new DepartmentComparator ());

That is never going to work; take this sequence for example: (B, 1) (A, 4) (B, 3) (A, 2). After you've sorted this on the leters the sequence may be (A, 4) (A, 2) (B, 1) (B, 3) and after you sort on the numbers the sequence can be (B, 1) (A, 2) (B, 3) (A, 4). You don't want that; you need to define a major and minor sort order and it was demonstrated by Camickr and Tolls; read their replies again.

kind regards,

Jos