Java Reference
In-Depth Information
The final modifier specifies that the class may not be extended. A class cannot
be declared to be both abstract and final .
If a class is declared strictfp , all its methods behave as if they were declared
strictfp . This modifier is extremely rarely used.
Fields and Methods
A class can be viewed as a collection of data (also referred to as state ) and code to
operate on that state. The data is stored in fields, and the code is organized into
This section covers fields and methods, the two most important kinds of class mem‐
bers. Fields and methods come in two distinct types: class members (also known as
static members) are associated with the class itself, while instance members are
associated with individual instances of the class (i.e., with objects). This gives us
four kinds of members:
• Class fields
• Class methods
• Instance fields
• Instance methods
The simple class definition for the class Circle , shown in Example 3-1 , contains all
four types of members.
Example 3-1. A simple class and its members
public class Circle {
// A class field
public static final double PI = 3.14159 ; // A useful constant
// A class method: just compute a value based on the arguments
public static double radiansToDegrees ( double radians ) {
return radians * 180 / PI ;
// An instance field
public double r ; // The radius of the circle
// Two instance methods: they operate on the instance fields of an object
public double area () { // Compute the area of the circle
return PI * r * r ;
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