Comparable In collections

public class Employee implements Comparable<Employee> {

private int empno;
private String ename;
private double sal;

public int getEmpno() {
return empno;
}

public void setEmpno(int empno) {
this.empno = empno;
}

public String getEname() {
return ename;
}

public void setEname(String ename) {
this.ename = ename;
}

public double getSal() {
return sal;
}

public void setSal(double sal) {
this.sal = sal;
}

public Employee(int empno, String ename, double sal) {
super();
this.empno = empno;
this.ename = ename;
this.sal = sal;
}

@Override
public String toString() {
return "Employee [empno=" + empno + ", ename=" + ename + ", sal=" + sal
+ "]";
}

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

public static void main(String[] args) {
Employee employee = new Employee(101, "nari", 190);
System.out.println(employee);

}

}