Reference Types Supported in Java

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∟Reference Types Supported in Java

This section provides a list of reference types supported in Java: class type, interface type, type variable and null.

Other than primitive types, Java also supports several reference types as shown below:

Data Types
|
|- Primitive Types
|  |...
|
|- Reference Types
   |
   |- Class Type
   |  |- Enum Type
   |
   |- Interface Type
   |  |- Annotation Type
   |
   |- Type Variable
   |
   |- Array Type
   |
   |- null

1. Class Type - A class type is a reference type representing objects whose behaviors are defined in the corresponding class. For example, java.lang.String is a class type.

1.1. Enum Type - A enum type is a special kind of class type that has a set of pre-defined instances representing a set of static values called enum constants.

2. Interface Type - An interface type is a reference type representing objects whose behaviors are defined in the corresponding interface. For example, java.lang.Runnable is an interface type.

2.1. Annotation Type - A Annotation type is a special kind of interface type that defined by a "@interface" declaration statement (also called annotation declaration statement).

3. Type Variable - A type variable is a reference type representing objects whose type will be determined at execution time, not at the compilation time. Type variable is introduced in JDK 5 to create generic classes, generic interfaces and generic methods. For example, T is a type variable in "public class Box<T> {private T t;...}".

4. Array Type - An array type is a reference type representing objects of arrays of a primitive type or a reference type. For example, int[], String[] are array types.