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Trail: Learning the Java Language
Lesson: Classes and Objects
Section: Classes
Classes and Objects
Classes
Declaring Classes
Declaring Member Variables
Defining Methods
Providing Constructors for Your Classes
Passing Information to a Method or a Constructor
Objects
Creating Objects
Using Objects
More on Classes
Returning a Value from a Method
Using the this Keyword
Controlling Access to Members of a Class
Understanding Instance and Class Members
Initializing Fields
Summary of Creating and Using Classes and Objects
Questions and Exercises
Questions and Exercises
Nested Classes
Inner Class Example
Summary of Nested Classes
Questions and Exercises
Enum Types
Questions and Exercises
Annotations
Questions and Exercises
Home Page > Learning the Java Language > Classes and Objects
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Declaring Classes

> You've seen classes defined in the following way:

> >     class MyClass {
> >         //field, constructor, and method declarations
> >     }

> This is a class declaration. The class body (the area between the braces) contains all the code that provides for the life cycle of the objects created from the class: constructors for initializing new objects, declarations for the fields that provide the state of the class and its objects, and methods to implement the behavior of the class and its objects.

> The preceding class declaration is a minimal one—it contains only those components of a class declaration that are required. You can provide more information about the class, such as the name of its superclass, whether it implements any interfaces, and so on, at the start of the class declaration. For example,

> >     class MyClass extends MySuperClass implements YourInterface {
> >         //field, constructor, and method declarations
> >     }

> means that `MyClass` is a subclass of `MySuperClass` and that it implements the `YourInterface` interface.

> You can also add modifiers like public or private at the very beginning—so you can see that the opening line of a class declaration can become quite complicated. The modifiers public and private, which determine what other classes can access `MyClass`, are discussed later in this lesson. The lesson on interfaces and inheritance will explain how and why you would use the extends and implements keywords in a class declaration. For the moment you do not need to worry about these extra complications.

> In general, class declarations can include these components, in order:

> 1. Modifiers such as public, private, and a number of others that you will encounter later.
> 2. The class name, with the initial letter capitalized by convention.
> 3. The name of the class's parent (superclass), if any, preceded by the keyword extends. A class can only extend (subclass) one parent.
> 4. A comma-separated list of interfaces implemented by the class, if any, preceded by the keyword implements. A class can implement more than one interface.
> 5. The class body, surrounded by braces, {}.

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