Comparable vs Comparator

• Comparable interface can be used to provide single way of sorting whereas Comparator interface is used to provide different ways of sorting.
• For using Comparable, Class needs to implement it whereas for using Comparator we don’t need to make any change in the class.
• Comparable interface is in java.lang package whereas Comparator interface is present in java.utilpackage.
• We don’t need to make any code changes at client side for using Comparable, Arrays.sort() or Collection.sort() methods automatically uses the compareTo() method of the class. For Comparator, client needs to provide the Comparator class to use in compare() method.

public class Employee implements Comparable<Employee> {

    private Long id;

    private String name;

    private Double salary;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Double getSalary() {
        return salary;
    }

    public void setSalary(Double salary) {
        this.salary = salary;
    }

    public Employee() {
    }

    public Employee(Long id, String name, Double salary) {
        this.id = id;
        this.name = name;
        this.salary = salary;
    }

    @Override
    public int compareTo(Employee o) {
        return (int) (this.id - o.id);
    }

    @Override
    public String toString() {
        return new ToStringBuilder(this)
                .append("id", id)
                .append("name", name)
                .append("salary", salary)
                .toString();
    }
}

public static void main(String[] args) {

        List<Employee> employeeList = new ArrayList<>();
        employeeList.add(new Employee(13L, "hello", 8000D));
        employeeList.add(new Employee(17L, "world", 10000D));
        employeeList.add(new Employee(13L, "test", 12000d));
        employeeList.add(new Employee(14L, "demo", 15000D));

        Collections.sort(employeeList);

        for (Employee e : employeeList) {

            System.out.println(e);
        }

        Collections.sort(employeeList, new Comparator<Employee>() {
            @Override
            public int compare(Employee o1, Employee o2) {
                int flag = (int) (o1.getId() - o2.getId());
                if (flag == 0) {
                    flag = (int) (o2.getSalary() - o1.getSalary());
                }

                return flag;
            }
        });

        System.out.println("comparator sort:");

        for (Employee e : employeeList) {

            System.out.println(e);
        }

    }

Employee@4d76f3f8[id=13,name=hello,salary=8000.0]
Employee@2d8e6db6[id=13,name=test,salary=12000.0]
Employee@23ab930d[id=14,name=demo,salary=15000.0]
Employee@4534b60d[id=17,name=world,salary=10000.0]
comparator sort:
Employee@2d8e6db6[id=13,name=test,salary=12000.0]
Employee@4d76f3f8[id=13,name=hello,salary=8000.0]
Employee@23ab930d[id=14,name=demo,salary=15000.0]
Employee@4534b60d[id=17,name=world,salary=10000.0]