Add Object to array list. Get error when try add obect to ArrayList

Could somebody answer why there is a problem with my array list. I have a classes: List, People and Main (to run everything).

In List I am creating a new ArrayList to hold objects of type People.

In Main I am making new List object, then make new People object and then calling from List object add method, and at this point I get a nullPointerException exception.

public class Main {
    public static void main(String[] args) {

        List l = new List();       // making new List object 
        People p = new People();   // making new People objec开发者_如何转开发t

        l.addPeople(p);           // calling from List object "addPeople" method and
    }            

                 // parsing People object "p"
 }




import java.util.ArrayList;

public class List {

        public List(){           //constructor
    }

        ArrayList<People>list;      // new ArrayList to hold objects of type "People"

    public void addPeople(People people){   
        list.add(people);               // I get error here
    }
} 

public class People {

    public People(){         // constructor
    }
}

In the constructor:

list = new ArrayList<People>();

You did not instantiate the list at any time. In your constructor do this:

   public List(){           //constructor
          list = new ArrayList<People>();
   }

I'm not sure if this is relevant, but it's a bad idea to name your class "List" since this will hide the List interface.

You need to put an ArrayList instance into your list field.