ClassDeclaration

A class declaration is a language construct used to introduce a new class type. It specifies the class name, optional type parameters, and, where supported, its place in an inheritance hierarchy and the interfaces it implements. The declaration defines the class’s structure and behavior and serves as a blueprint for creating objects.

Most languages support modifiers such as public, private, or protected, plus modifiers like abstract or sealed/final. The class declaration includes the class keyword (or equivalent), the name, and optional inheritance and interface clauses, for example: class Foo extends Bar implements Baz.

The class body contains member declarations, including fields or properties, constructors, methods, events, and nested types. Many languages also support generics, so a class can be declared with type parameters.

Semantics: abstract classes may declare abstract members and cannot be instantiated; sealed/final classes cannot be subclassed; static members belong to the class rather than any instance.

Language variants illustrate differences. Java/C#: public class Person extends LivingBeing implements Serializable { private String name; public Person(String name) { this.name = name; } } demonstrates a typical single inheritance plus interfaces approach. Python uses a different syntax: class Person(LivingBeing): def __init__(self, name): self.name = name. TypeScript uses: class Person extends LivingBeing implements Serializable { private name: string; constructor(name: string) { super(); this.name = name; } }.

In all forms, a class declaration serves to define a comparable object type, its visibility, inheritance relations, and the members that instances of the class will possess.