Java in a Nutshell, 5th Edition [Electronic resources] نسخه متنی

3.1. Class Definition Syntax

At
its simplest level, a class definition consists of the
keyword
class followed by the name of the class and a set
of class members within curly braces. The class
keyword may be preceded by modifier keywords and annotations (see
Chapter 4). If the class extends another class,
the class name is followed by the extends keyword
and the name of the class being extended.
If the class
implements one or more interfaces then the class name or the
extends clause is followed by the
implements

keyword and a comma-separated list of interface names. For example:

public class Integer extends Number implements Serializable, Comparable {
// class members go here
}

Generic class declarations include additional syntax that is covered
in Chapter 4.

Class declarations may include zero or more of the following

modifiers:

public

A public class is visible to classes
defined outside of its package. See Section 3.6 later in this chapter.

abstract

An
abstract class is one whose implementation is
incomplete and cannot be instantiated. Any class with one or more
abstract methods must be declared
abstract.

final

The final modifier
specifies that the class may not be extended. Declaring a class
final may enable the Java VM to optimize its
methods.

strictfp

If a class is declared
strictfp, all its methods behave as if they
were declared strictfp. This rarely used modifier
is discussed in Section 2.6 in
Chapter 2.

A class cannot be both abstract and
final. By convention, if a class has more than one
modifier, they appear in the order shown.