Java: Sorting objects in an ArrayList with conditions

Question

I want to sort my ArrayList alphabetically. Therefore I wrote a sortEmployees method. In case my employees have the same name I'd like to sort them based on their salary, which means that the employee with the higher salary should be printed out first.

Well, I successfully managed to sort them alphabetically, but I don't know how I can compare, if employees have the same name and if that is the case, the employee with the higher salary shall be printed. Thanks.

ArrayList<Employee> employees = new ArrayList<Employee>();

public void sortEmployees(){
    Collections.sort(employees, (p1, p2) -> p1.name.compareTo(p2.name));
    for(Employee employee: employees){
        System.out.println("ID: " + employee.ID + END_OF_LINE + "Name: "+employee.name + END_OF_LINE + "Salary: " + employee.grossSalary);
        System.out.println(""); // just an empty line
    }
}

You're almost there. Modify your comparator such that If `compareTo()` is non-zero use this value, otherwise compare the salaries and use that value. — dave, Oct 10 '17 at 23:51
Sorry I didn't quite get it. Do you mind showing me that in code? — user1234567890, Oct 11 '17 at 00:02
`Comparator.comparing(e -> e.name).thenComparingInt(e -> e.grossSalary)` — shmosel, Oct 11 '17 at 00:24

score 2 · Accepted Answer · answered Oct 10 '17 at 23:52

Create an appropiate Comparator that will compare two items according to your desired criteria. Then use Collections.sort() on your ArrayList.

If at a later time you want to sort by different criteria, call Collections.sort() again with a different Comparator.

Reference: How to sort an ArrayList using multiple sorting criteria?

Just an advice for future questions, please google properly or search on stackoverflow for your problem before asking a new question. Most of the time such trivial questions have already been asked and answered.

@JavaTeachMe2018 Did you figure it out or do you want me to edit my answer? — unrealsoul007, Oct 13 '17 at 21:36

score 1 · Answer 2 · answered Oct 11 '17 at 00:20

I assume that you have the method equals to return whether two names are equal. You can define your Comparator as follows:

ArrayList<Employee> employees = new ArrayList<Employee>();

public void sortEmployees(){
  Collections.sort(employees, new Comparator<Employee>() {
    @Override 
    public int compare(Employee a, Employee b) {
      if (a.name.equals(b.name)) {
        return b.salary - a.salary;
      } else {
        return p1.name.compareTo(p2.name);
      }
    }
  });
  for(Employee employee: employees){
    System.out.println("ID: " + employee.ID + END_OF_LINE + "Name: "+employee.name + END_OF_LINE + "Salary: " + employee.grossSalary);
    System.out.println(""); // just an empty line
  }
}

While this looks correct, I think it would be better to use a _lambda_, rather than create a `Comparator`. It's less code and fits in with the OP's current implementation. — dave, Oct 11 '17 at 00:45

Java: Sorting objects in an ArrayList with conditions

2 Answers2