如何访问另一个类的arraylist

Question

Suppose I have a class manager which stores Arraylist of class Employee say:

class Manager {

    ArrayList<Employee> x = new ArrayList<>();
}

Now is it possible to get the name of Manager object by some method in Employee class? In other words, finding the name of Arraylist using element.

Answer 1

If you want to get the manager object from employee object then you have to implement bi directional mapping. Add manager attribute in employee class as well.

Answer 2

The problem as I understand, is to find the manager of a given employee. To do this you'll need a list of all managers and the details of the employee you search the manager for.

class Manager
    {
       private String name;
       private List<Employee> employees;

       public List<Employee> getEmployees()
       {
         return this.employees;
       }

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

If you are using existing object of an Employee (You get the Employee object out of a list of employees in a Manager object), following approach will work.

class FunctionClass{
   public static void main(String[] args)
   {
      List<Manager> allManagers = getAllManagers();
      Employee currEmployee = getCurrentEmployee();

      for( Manager manager : allManagers )
      {
         if( manager.getEmployees().contains( currEmployee ) )
         {
            System.out.println( manager.getName() );
            break;
         }
      }
   }
}

If you are creating objects of Employee from provided data, above approach will not work. You will have to iterate through all the employees of each manager.

class FunctionClass{
       public static void main(String[] args)
       {
          List<Manager> allManagers = getAllManagers();
          Employee currEmployee = getCurrentEmployee();

          for( Manager manager : allManagers )
          {
             for( Employee emp: manager.getEmployees() )
             {
                if( /*compare if emp and currEmployee equal*/ )
                {
                  System.out.println( manager.getName() );
                  break;
                }
          }
       }
    }