Working with Objects - Java 6 - page 62

the orderTotal instance variable itself holds an object, and that object has its own
instance variable called layaway , you could refer to it as in this statement:

boolean onLayaway = myCustomer.orderTotal.layaway;

Dot expressions are evaluated from left to right, so you start with myCustomer 's variable
orderTotal , which points to another object with the variable layaway . You end up with
the value of that layaway variable.

Changing Values
Assigning a value to that variable is equally easy; just tack on an assignment operator to
the right side of the expression:

myCustomer.orderTotal.layaway = true;

This example sets the value of the layaway variable to true .

Listing 3.2 is an example of a program that tests and modifies the instance variables in a
Point object. Point , a class in the java.awt package, represents points in a coordinate
system with x and y values.

LISTING 3.2 The Full Text of PointSetter.java

1: import java.awt.Point;
2:
3: class PointSetter {
4:
5: public static void main(String[] arguments) {
6: Point location = new Point(4, 13);
7:
8: System.out.println(“Starting location:”);
9: System.out.println(“X equals “ + location.x);
10: System.out.println(“Y equals “ + location.y);
11:
12: System.out.println(“\nMoving to (7, 6)”);
13: location.x = 7;
14: location.y = 6;
15:
16: System.out.println(“\nEnding location:”);
17: System.out.println(“X equals “ + location.x);
18: System.out.println(“Y equals “ + location.y);
19: }
20: }