Sorting on Multiple fields -- Its working, but not able to understand how is it working.

class Employee implements Comparable{
     private String name;
         private String gender;
 
         Employee(String name, String gender) {
             this.name = name;
             this.gender = gender;
         }
 
         public String getName() {
                 return name;
         }
 
         public void setName(String name) {
             this.name = name;
         }
 
         public String getGender() {
                 return gender;
         }
 
         public void setGender(String gender) {
                 this.gender = gender;
         }
 
         public String toString() {
             return this.getName() + " : " + this.getGender();
         }
 
         @Override
         public int compareTo(Object o) {
             int gendarComp=this.getGender().compareTo(((Employee)o).getGender());
             return (gendarComp!=0?gendarComp:this.name.compareTo(((Employee)o).getName()));
         }
     } 
 
     class EmployeeExec {
         public static void main(String[] args) {
             List allEmpls = new ArrayList();
             allEmpls.add(new Employee("vijay", "m"));
             allEmpls.add(new Employee("balaji", "m"));
             allEmpls.add(new Employee("shaifali", "f"));
             allEmpls.add(new Employee("archana", "f"));
             allEmpls.add(new Employee("alala", "m"));
             allEmpls.add(new Employee("kiran", "f"));
 
             sortEmployees(allEmpls);
         }
 
         public static void sortEmployees(List allEmpls) {
             Collections.sort(allEmpls);
             System.out.println(allEmpls);
         }
     }
 

Can any one Please help me in understanding how it is working? what is the funda to sort. I kept some sysout statements to see, but I dont really understand how it is getting called. I know its working with merge sort. but how? please help me.

-Balaji

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