Java - how to sort object in many ways: Arrays.sort(), Comparable

Question

Let\'s say that I have an array with objects, where I have some employees (objects). They all have: int age, double salary. I want to sort this arr

Answer 1

You should use two Comparator classes instead of implementing Comparable.

In short, a class that implements Comparable will be comparable in a single aspect to instances of that class.

A class that implements Comparator will be a comparator medium for some other class. This means you can have multiple comparators to compare classes for different aspects. Furthermore, a Comparator class can be passed to a sort method, such as Collections.sort() or Arrays.sort(), to allow precise control over the sort order and can also be used to control the order of certain data structures, such as sorted sets or sorted maps.

To serve your purpose, what you could do is create two Comparator classes like:

class SalaryComparator implements Comparator {
    int compare(Employee a, Employee b) {
        return Double.compare(a.salary, b.salary);
    }
}

class AgeComparator  implements Comparator {
    int compare(Employee a, Employee b) {
        return Integer.compare(a.age, b.age);
    }
}

And then when calling a sorting method you pass in a Comparator you would like to use.

For example, if you had an ArrayList list and you want to sort it by salary you can do something like:

 Collections.sort(list, new SalaryComparator()); // sort the list by salaries

Or if you had an Employee[] array and you want to sort it by age for example:

Arrays.sort(array, new AgeComparator()); // sort the array by age