Question

When i try to create an instance of a class and add this to my arraylist i can’t call methods defined in the child.

How do i make this work?

List class:

import java.util.*;
public class List {
  private ArrayList<Person> persons;
  public List(){
    persons = new ArrayList<Person>();
  }
  public void addAssistant(){
    Person person = new Assistant();
    persons.add(person);
    if(person instanceof Assistant){
      person.assist();
    }
  }
}

Person class:

public class Person {
  public Person(){}
}

Assistant class:

public class Assistant extends Person {
  public Assistant(){}
  public void assist(){
     System.out.println("I am assisting!");
  }
}

Compiler:
line: person.assist(); within the addAssistant() method in the List class.

Compiler error:
The compiler cannot find symbol – method assist().

Answer 1

You need an explicit cast:

if(person instanceof Assistant){
  ((Assistant)person).assist();
}

However, I think this type of logic should generally be discouraged.