There are several ways to define your classes. The simplest would be:

class YourClass {

declare your field, constructor, and methods here

}

You can also define them in a more complex manner: 

class YourClass extends YourSuperClass implements SomeInterface {

declare your field, constructor, and methods here

}

Here is a list of components class declarations can contain:

• Public, Private, and other modifiers.

• Class Name.

• Superclass name, if applicable with the keyword extends before it.

• The keyword implements followed by a list of interfaces (separated by commas).

• Body of the class, encapsulated with braces{}.

Variables in Classes

We discussed variables and data types in a previous article, but they need a little further discussion here, as they relate to classes.

Variables in classes are known as member variables and are called fields. They are composed of a modifier (such as public or private), a type, and a name. An example would be:

public int myEnormousIQ;

In the above example, the public portion of our declaration is known as an access modifier. It determines which classes have access to the member field. There are several access modifiers: public, protected, package, and private.

• Public: can be referenced from anywhere in the application by the class in which it is defined.

• Package: can be referenced by only the same package through the class in which it was defined.

• Private: can only be referenced by the class in which it was defined.

• Protected: can be referenced by its class and subclass and from its package.