- Draw a picture of the stack and the heap in order to help students understand:
- what really happens when they write their code.
- concepts like "mutable" and "deep vs. shallow copy."
- Sometimes students will say they understand the stack and heap diagrams, but they have an ah-ha moment after acting out how variables are passed between methods.
- Activity Prep:
- Create a paper drawing or cutout of a cat.
- You could use something else to represent the variable, the using a cat to represent a cat will help students make the connection.
- Create a stack of papers that says "Cat c" to represent the cat drawing.
- Activity:
- Write the following code on the board:
public static void main(String args[]){ Cat c = new Cat("sam", 9); System.out.println(c); foo(c); System.out.println(c); } public void foo(Cat cat){ cat.moreLives(1); }- Introduce the class to your drawing that is representing "Cat c".
- Ask for a volunteer to be the pointer to "Cat c", this student will point to the cat on the board and hold the paper that says "Cat c"
- Ask for a volunteer to represent the "foo" method.
- Now, have the student pointing to "Cat c" representation, give one "Cat c" card to the student representing the "foo" method.
- Make sure the "Cat c" representative is still pointing to the cat on the board.
- The "foo" method student will draw a new number of lives on the "Cat c" object.
- Then have the student representing foo walk away.