— Scott McNealy, Sun Microsystems Chairman, President and ceo

}
public class Life {
int size;
public void setSize(int s) {
size = s;
// ‘s’ disappears at the 
// end of this method,
// but ‘size’ can be used
// anywhere in the class
}
}
Variable ‘s’ (this time a method parameter) 
is in scope only within the setSize() 
method. But instance variable size is 
scoped to the life of the object as opposed 
to the life of the method.
BAD!! Not legal to 
use ‘s’ here!
The variable ‘s’ is alive, but in scope only within the 
read() method. When sleep() completes and read() is 
on top of the Stack and running again, read() can 
still see ‘s’. When read() completes and is popped off 
the Stack, ‘s’ is dead. Pushing up digital daisies.
sleep() can’t see the ‘s’ variable. Since 
it’s not in sleep()’s own Stack frame, 
sleep() doesn’t know anything about it.
object 
lifespan

---

constructors and 
gc
you are here
4
259
public void doStuff() {
boolean b = true;
go(4);
}
public void go(int x) {
int z = x + 24;
crazy();
// imagine more code here
}
public void crazy() {
char c = ‘a’;
}
doStuff()
b
go()
doStuff()
b
x z
crazy()
c
doStuff()
b
go()
x z
go()
doStuff()
b
x z
1
doStuff() goes on the 
Stack. Variable ‘b’ is 
alive and in scope.
go() plops on top of 
the Stack. ‘x’ and ‘z’