Classes

In Java (and many other object-oriented programming languages) classes have two purposes:

They declare a type (a reference type in Java) from which objects can be instantiated.

They are the main units of encapsulation for information hiding.

Classes consist of a name, constructors, a set of methods, and a set of instance variables (or attributes).

Syntax in Java: Modifier class Identifier { Declarations }

The modifier is usually public for top-level classes.

Top-level classes should be stored in files carrying their name. The class BankAccount, for example, should be stored into a file named BankAccount.java. This allows the Java compiler to find the declaration of BankAccount if it is used elsewhere.