Introduction to Objects - Advanced Topics in Java: Core Concepts in Data Structures - page 41

Suppose we create a part with this:

Part af = new Part("Air Filter", 8.75);

The expression af.printPart() would display the following:

Name of part: Air Filter
Price: $8.75

When printPart is called via af , the references in printPart to the fields name and price become references to
the fields of af . This is illustrated in Figure 2-4 .

name: Air Filter

725
af

price: 9.50

printPart()

System.out.printf("\nName of part: %s\n", name);
System.out.printf("Price: $%3.2f\n", price);

Figure 2-4. name and price refer to the fields of af

2.5.2 Using a Static Method
We could, if we want, write printPart as a static method, which will be called with p as an argument in order to print
its fields. In this case, we will write the following:

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

The field names have to be qualified with the object variable p . Without p , we would have the case of a static
method referring to a non-static field, which is forbidden by Java.
If c is a Part object created in a user class, we will have to use the following to print its fields:

Part.printPart(c);

This is slightly more cumbersome than using the instance method, shown previously. By comparison, you can
use, for instance, Character.isDigit(ch) to access the static method isDigit in the standard Java class Character .

2.5.3 Using the toString() Method
The toString method returns a String and is special in Java. If we use an object variable in a context where a string is
needed, then Java will attempt to invoke toString from the class to which the object belongs. For example, suppose
we write the following, where p is a Part variable:

System.out.printf("%s", p);