How to use Java comparator properly?

Question

If I have the following class:

public class Employee {
    private int empId;
    private String name;
    private int age;

    public Employee(int empId, String name, int age) {
        // set values on attributes
    }
    // getters & setters
}

How can I use comparator that compares by name, then age, then id?

Answer 1

Use this:

public class Test 
{
    public static void main(String[] args) 
    {
        Employee emp1 = new Employee(2, "Tom", 20);
        Employee emp2 = new Employee(1, "Tom", 20);
        Employee emp3 = new Employee(3, "Hank", 21);

        List<Employee> list = new ArrayList<>();

        list.add(emp1);
        list.add(emp2);
        list.add(emp3);

        Collections.sort(list, new Employee().new MyComparator());

        System.out.println(list);
    }
}

class Employee 
{
    private int empId;
    private String name;
    private int age;

    public Employee()
    {}

    public Employee(int empId, String name, int age) 
    {
        this.empId = empId;
        this.name = name;
        this.age = age;
    }

    class MyComparator implements Comparator<Employee>
    {
        @Override
        public int compare(Employee e1, Employee e2) 
        {
            if(e1.name.compareTo(e2.name) == 0)
            {
                if(((Integer)e1.age).compareTo(e2.age) == 0)
                {
                    return ((Integer)e1.empId).compareTo(e2.empId);
                }
                else
                {
                    return ((Integer)e1.age).compareTo(e2.age);
                }
            }
            return e1.name.compareTo(e2.name);
        }
    }

    @Override
    public String toString() 
    {
        return "Employee [empId=" + empId + ", name=" + name + ", age=" + age + "]";
    }
}