The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
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 beginningso 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: