identifier of an instance was altered from 1 to 2

What I am trying to do is read a text file in the code and insert it into a table called employee1. And I am getting this error:

Hibernate: insert into EMPLOYEE1 (NAME, SALARY, MANAGER, ID) values (?, ?, ?, ?) identifier of an instance of com.Employee altered from 1 to 2 Exception in thread "main" org.hibernate.HibernateException: identifier of an instance of com.Employee altered from 1 to 2 at org.hibernate.event.def.DefaultFlushEntityEventListener.checkId(DefaultFlushEntityEventListener.java:51) at org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:82) at org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:190) at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:70) at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:26) at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:669) at roseindia.tutorial.hibernate.FirstExample.main(FirstExample.java:98)

Code of the Employee.java

public class Employee 
{

    private int id;
    private String name;
    private double salary;
    private String manager;


    public int getId() 
    {
        return id;
    }

    public void setId(int s) 
    {
        id = s;
    }
    //***************************************************//  
    public String getName() 
    {
        return name;
    }

    public void setName(String s) 
    {
        name = s;
    }
    //***************************************************//  
    public double getSalary() 
    {
        return salary;
    }

    public void setSalary(double s) 
    {
        salary = s;
    }
    //***************************************************//
    public String getManager() 
    {
        return manager;
    }

    public void setManag