One Order Class, Three Orders

Three objects made from one class, and one of them cancelled. Watch which values move and which stay put.

java

Order a = new Order();
a.customer = "Ada";

Order b = new Order();
b.customer = "Grace";

Order c = a;

a.cancel();

System.out.println(a.status + " " + b.status + " " + c.status);

text

cancelled open cancelled

b is untouched, because it is a different object with its own status. c changed, because line 7 did not make a third order — it copied an address, so a and c are two names for one object.

Three variables, and how many objects there actually are
Variable	Points at	Own status
`a`	The first order	Shared with `c`
`b`	The second order	Its own
`c`	The first order	Shared with `a`

What to notice: new is the only thing in Java that creates an object. Every other line moves addresses around, which is why counting the new keywords tells you how many objects exist.

Java
Object-Oriented Programming