class actor { 
actor
public static final int Person = 0; public static final int Student = 1; public static final int Employer = 2; public static final int Final = 3; public void walk() { if (exists()) self().walk(); } public void talk() { if (exists()) self().talk(); } public void think() { if (exists()) self().think(); } public void act() { if (exists()) self().act(); } public boolean exists() { return false; } public actor self() { return this; } public void become(actor A) { } public void become(int R) { } };

slide: actor.java