— Scott McNealy, Sun Microsystems Chairman, President and ceo

public class Duck {
int size;
}
Every Duck has a “size” 
instance variable.
Local variables are declared inside a method, including 
method parameters. They’re temporary, and live only as 
long as the method is on the stack (in other words, as long as 
the method has not reached the closing curly brace).
public void foo(int x) {
int i = x + 3;
boolean b = true; 
}
The parameter x and 
the variables i and b 
are all local variables.
the 
stack
 and the 
heap

---

constructors and 
gc
you are here
4
237
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’;
}
Methods are stacked
When you call a method, the method lands on 
the top of a call stack. That new thing that’s 
actually pushed onto the stack is the stack 
frame, and it holds the state of the method 
including which line of code is executing, and 
the values of all local variables. 
The method at the top of the stack is always 
the currently-running method for that stack 
(for now, assume there’s only one stack,but in 
chapter 14 we’ll add more.) A method stays on 
the stack until the method hits its closing curly 
brace (which means the method’s done). If 
method
 foo() calls method bar(), method bar() is 
stacked on top of method foo().
bar()
foo()
stack frames
bottom of the stack
top of the stack
local variables 
(including 
parameter x)
A call stack with two methods