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, S         


        

Answer 1

Implement it

public class Employee {
    private int empId;
    private String name;
    private int age;
    /**
     * @param empId
     * @param name
     * @param age
     */
    public Employee(int empId, String name, int age) {
        super();
        this.empId = empId;
        this.name  = name;
        this.age   = age;
    }
    /**
     * 
     */
    public Employee() {
        super();
        // TODO Auto-generated constructor stub
    }


    public int getEmpId() {
        return empId;
    }
    public void setEmpId(int empId) {
        this.empId = empId;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }

    //Compare by name, age and then id
    public static Comparator<Employee> COMPARE_EMPLOYEE = new Comparator<Employee>() {
        public int compare(Employee one, Employee other) {
            //Compare Name
            if (one.getName().compareToIgnoreCase(other.getName()) == 0) {
                //Compare age
                if((one.getAge() - other.getAge()) == 0) {
                    // Now check with id is useless
                    // So directly return result of compare by id
                    return one.getEmpId() - other.getEmpId();
                } else { //If age Not equal
                    return one.getAge() - other.getAge();
                }
            } else { //If name not equal
                return one.getName().compareToIgnoreCase(other.getName());
            }
        }
    };
}

Use :

List<Employee> contacts = new ArrayList<Employee>();
//Fill it.

//Sort by address.
Collections.sort(contacts, Employee.COMPARE_EMPLOYEE);

Read Sorting an ArrayList of Contacts , this must help you and you will get more ideas and different different types of use of Comparator.