Class

A class is a blueprint for objects and defines a type with fields and methods.

Related concepts:  ObjectFieldMethodMemberTypePrototype

Closest Wikipedia entry:  Class (computer programming) — In object-oriented programming, a class is an extensible program-code-template for creating objects, providing initial values for state (member variables) and implementations of behavior (member functions or methods).When an object is created by a constructor of the class, the resulting object is called an instance of the class, and the member variables specific to the object are called instance variables, to contrast with the class variables shared across the class. In certain languages, classes are, as a matter of fact, only a compile time feature (new classes cannot be declared at run-time), while in other languages classes are first-class citizens, and are generally themselves objects (typically of type Class or similar). In these languages, a class that creates classes within itself is called a metaclass.

Misconceptions about Class

28 documented Misconceptions

AbstractClassMustImplementAbstractMethod

An abstract class must implement all abstract methods defined in its superclass

AbstractClassNoImplementation

An abstract class cannot contain implemented methods

AddMemberAtRuntime

Set of class members can change at runtime

AllClassesHaveDefaultConstructor

All classes automatically get a no-argument constructor

AnyClassException

Any class can be an exception class

ArrayListIsArray

ArrayLists are arrays

CallNotStaticallyChecked

A method invocation on a reference of a type that does not have that method won't compile

ConcreteClassMustOverride

A concrete class needs to implement all methods declared in its abstract superclasses

ConcreteClassOnlyImplementClassAbstract

A concrete class only needs to implement those abstract methods it inherits from abstract superclasses

ConcreteClassOnlyImplementDirectAbstract

A concrete class only needs to implement abstract methods declared in its direct supertypes

ConcreteClassOnlyImplementInterfaceAbstract

A concrete class only needs to implement those abstract methods it inherits from interfaces

ImmutableRequiresFinalParameters

Immutable classes need final constructor/method parameters

ImplicitInterfaceImplementation

Java implicitly produces implementations of any methods a class inherits from the interfaces it implements

InterfaceExtendClass

An interface can extend a class

MethodAsField

Each object contains its own special fields for all of its methods

MethodsWithoutClass

Methods can be defined outside a class

MultipleSuperclasses

A class can have multiple superclasses

NestedObjectsImplyNestedClasses

If objects are part of a containment hierarchy, their classes are nested, too

NoFieldInheritance

An object contains only the fields declared in its class

NoMethodInheritance

Subclasses inherit fields but not methods

PrivateFieldsImplyImmutability

A class where all fields are private is immutable

ReferringToRecursiveStructureMakesRecursive

A class referring to a recursive data structure is (indirectly) part of that recursion as well

SetterIsStatic

Setter methods are static

SuperclassObjectAllocated

When instantiating an object of a subclass, an object of a superclass is also allocated

UnqualifiedNamesMustDiffer

The unqualified names of different classes must be different

UseOfSelfTypeImpliesRecursiveType

If a class has a method that has a local variable, parameter, or return value with the class as its type, the class is a recursive type