List of objects that implement this interface can be sorted automatically by sort method of the list interface. This interface has compareTo() method that is used by the sort() method of the list.
In this code Employee class is implementing Comparable interface and have method compareTo(). ComparableDemo.java is showing the use of this interface. This class first makes a list of objects of type Employee and call sort method of java.util.Collections, which internally uses compareTo() method of Employee class and sort the list accordingly.
If you defined Comparable<T>, you need to use Employee e in function ‘publicint compareTo(Employee e) {‘ argument.
package algorithms;
publicclass Employee implements Comparable<Employee>{
intEmpID;
String Ename;
doubleSalary;
staticinti;
public Employee(String ename,double salary){
EmpID=i++;
Ename=ename;
Salary=salary;
}
public String toString(){
return"EmpID:" +EmpID+"\n"+"Ename:"+Ename+"\n"+"Salary:"+Salary;
}
@Override
publicint compareTo(Employee e) {
// TODO Auto-generated method stub
if(this.Salary==((Employee)e).Salary){
return 0;
}elseif((this.Salary)>((Employee)e).Salary){
return 1;
}else{
return -1;
}
}
}
package algorithms;
import java.util.*;
publicclass EmployeeDemo {
publicstaticvoid main(String[] args){
List ts1 = new ArrayList();
ts1.add(new Employee("Tom",40000.00));
ts1.add(new Employee ("Harry",20000.00));
ts1.add(new Employee ("Maggie",50000.00));
ts1.add(new Employee ("Chris",70000.00));
Collections.sort(ts1);
Iterator itr=ts1.iterator();
while(itr.hasNext()){
Employee element=(Employee)itr.next();
System.out.println(element+"\n");
}
}
}
Output:
EmpID:1
Ename:Harry
Salary:20000.0
EmpID:0
Ename:Tom
Salary:40000.0
EmpID:2
Ename:Maggie
Salary:50000.0
EmpID:3
Ename:Chris
Salary:70000.0
