Introduction to Objects - Advanced Topics in Java: Core Concepts in Data Structures - page 40

This sets the price of Part object p to 24.95 . As before, the method will not allow an invalid price to be set. It will
validate the supplied price and print an appropriate message, if necessary. Using the constants declared in Section
2.4.1, here is setPrice :

public void setPrice(double p) {
if (p < MinPrice || p > MaxPrice) {
System.out.printf("Part: %s\n", name);
System.out.printf("Invalid price: %3.2f; Set to %3.2f\n", p, NullPrice);
price = NullPrice;
}
else price = p;
} //end setPrice

With this addition, we can think of Part p as shown in Figure 2-3 .

725

name
price

getName()
getPrice()

725
p

setPrice()

Figure 2-3. Part object with setPrice() added

Observe the direction of the arrow for setPrice ; a value is being sent from the outside world to the private field
of the object.
Again, we emphasize the superiority of declaring a field private and providing mutator/accessor methods for it
as opposed to declaring the field public and letting a user class access it directly.
We could also provide methods to increase or decrease the price by a given amount or by a given percentage.
These are left as exercises.
As another exercise, write mutator methods for the price and inStock fields of the Book class.

2.5 Printing an Object's Data
To verify that our parts are being given the correct values, we would need some way of printing the values in an
object's fields.

2.5.1 Using an Instance Method (the Preferred Way)
One way of doing this is to write an instance method ( printPart , say), which, when invoked on an object, will print
that object's data. To print the data for Part p , we will write this:

p.printPart();

Here is the method:

public void printPart() {
System.out.printf("\nName of part: %s\n", name);
System.out.printf("Price: $%3.2f\n", price);
} //end printPart