Why can I not override my method in Java?

This is my java DAO pattern program and I found an error which i cannot resolve. This is my full code, this shows method can not be override.

I can do everything but I don’t know what the problem is.

      public class Employee
    {

     private String name;
    private int emp_id;

    Employee(String name, int emp_id)
 {
     this.name = name;
      this.emp_id = emp_id;

  }
     public int getEmp_id(){
     return emp_id;
   }
   public void setEmp_id(int emp_id){
  this.emp_id=emp_id;
 }

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

File 2:

   import java.util.List;

      interface  EmployeeDao 
   {
    public List<Employee> getAllEmployee();
    public Employee getEmployee(int emp_id);
    public void updateEmployee(Employee employee);
    public void deleteEmployee(Employee employee);
 }

File 3:

   import java.util.ArrayList;
   import java.util.List;
   abstract class EmployeeDaoImpl implements EmployeeDao
   {
      List<Employee> employees;

      public EmployeeDaoImpl(){
        employees= new ArrayList<Employee>();
        Employee employee1 = new Employee("Rajat",0);
        Employee employee2 = new Employee("Rano",1);
        employees.add(employee1);
       employees.add(employee2);        
    }


        @Override
         public void deleteEmployee(Employee employee) {
         employees.remove(employee.getEmp_id());
          System.out.println("Employee: Emp_id" +employee.getEmp_id() + ", 
       deleted from database");
        }

        @Override
         public List<Employee> getAllEmployees() {
         return employees;

      }


        @Override
        public Employee getEmployee(int emp_id) {
       return employees.get(emp_id);
       }

       @Override
       public void updateEmployee(Employee emp_id) {
       employees.get(employee.getEmp_id()).setName(employee.getName());
       System.out.println("Employee: Emp_id " + employee.getEmp_id() + ", 
     updated in the database");
      }
   }

File 4:

     class MyImplimentation {
      public static void main(String[] args) {
      EmployeeDao employeeDao = new EmployeeDaoImpl();


      for (Employee employee : employeeDao.getAllEmployee()) {
       System.out.println("Employee: [Emp_id : " + employee.getEmp_id() + ", 
       Name : " + employee.getName() + " ]");
         }



       Employee employee =employeeDao.getAllEmployee().get(0);
       semployee.setName("Rahul");
       employeeDao.updateEmployee(employee);


      employeeDao.getEmployee(0);
      System.out.println("Employee: [Emp_id : " + employeet.getEmp_id() + ", 
     Name : " + employee.getName() + " ]");     
           }
     }