Introduction to Objects - Advanced Topics in Java: Core Concepts in Data Structures - page 50

Further, suppose a user class contains these statements:
Part af = new Part("Air Filter", 8.75);
printPart(af);
and suppose the first statement assigns the address 4000 , say, to af . When printPart is called, 4000 is copied to
a temporary location and this location is passed to printPart where it becomes known as p , the name of the formal
parameter. Since the value of p is 4000 , in effect it has access to the original object. In this example, the method simply
prints the values of the instance variables. But it could also change them, if it wanted.
Consider the following method in the class Part , which adds amount to the price of a part:
public static void changePrice(Part p, double amount) {
p.price += amount;
}
The user class can add 1.50 to the price of the Air Filter with this call:
Part.changePrice(af, 1.50);
As indicated earlier, the parameter p has access to the original object. Any change made to the object pointed to
by p is, in fact, a change to the original object.
We emphasize that the method cannot change the value of the actual argument af (since it has no access to it),
but it can change the object pointed to by af .
In passing, note that we have used this example mainly for illustrative purposes. In practice, it would probably be
better to write an instance method to change the price of a Part object.
2.11 Array of Objects
In Java, a String is an object. Therefore, an array of String s is, in fact, an array of objects. However, a String is a
special kind of object in Java and, in some ways, is treated differently from other objects. For one thing, a String is
immutable ; we cannot change its value. For another, we think of a String as having one field—the characters in
the string—whereas a typical object will have several. For these reasons, we take a look at arrays of objects other
than String s.
Consider the class Part defined previously. The class contains two instance variables defined as follows:
public class Part {
private String name; // instance variable
private double price; // instance variable
// methods and static variables
} //end class Part
It is helpful to recall what happens when we declare a Part variable p as in the following:
Part p;