— Scott McNealy, Sun Microsystems Chairman, President and ceo

boolean rem
ove(Object e
lem)
boolean cont
ains(Object e
lem)
boolean isEm
pty()
int indexOf(O
bject elem)
Object get(in
t index)
boolean add
(Object elem
)
// more

---

interfaces and 
polymorphism
you are here
4
209
So what’s in this ultra-super-megaclass Object?
Object
boolean equals()
Class getClass()
int hashCode()
String toString()
If you were Java, what behavior would you want every 
object to have? Hmmmm... let’s see... how about a 
method that lets you fi nd out if one object is equal 
to another object? What about a method that can 
tell you the actual class type of that object? Maybe a 
method that gives you a hashcode for the object, so 
you can use the object in hashtables (we’ll talk about 
Java’s hashtables in chapter 17 and appendix B). 
Oh, here’s a good one—a method that prints out a 
String message for that object. 
And what do you know? As if by magic, class Object 
does indeed have methods for those four things. 
That’s not all, though, but these are the ones we 
really care about.
Just SOME of the methods 
of class Object.
Dog a = new Dog();
Cat c = new Cat();

if (a.equals(c)) {
System.out.println(“true”);
} else {
System.out.println(“false”);
}
equals(Object o)
1
Cat c = new Cat();
System.out.println(c.getClass());
getClass()
2
File Edit Window Help Stop
% java TestObject
false
File Edit Window Help Faint