Java Tutorials - Herong's Tutorial Examples

∟Reference Data Types and Variables

This chapter provides tutorial notes and example codes on reference data types and variables. Topics include 5 reference data types; reference data type variables store references to objects; multiple variables referring to a single object; superclass-subclass relation; superinterface-subinterface relation; interface-class relation; type casting.

Reference Types Supported in Java

Creating Class Type Objects

Class Type Variables Storing References

Interface Type Variables

Class and Interface Hierarchy

Supertype and Subtype

Explicit and Implicit Type Casting

Type Casting Example Program

Type Casting Compile and Runtime Error

Conclusion:

• Java supports 5 reference data types: class type, interface, type variable, array type, and null;
• A class type variable stores the reference of an object of the same class.
• A interface type variable stores the reference of an object of a class that implements the interface.
• java.lang.Object is a superclass of all other classes.
• java.lang.Object is a supertype of all other class and interface types.
• Up casting (widening reference conversion) is always allowed.
• Down casting (narrowing reference conversion) is allowed only if the reference object is compatible with the subtype.

Table of Contents

 About This Book

 JDK - Java Development Kit

 Execution Process, Entry Point, Input and Output

 Primitive Data Types and Literals

 Control Flow Statements

 Bits, Bytes, Bitwise and Shift Operations

 Managing Bit Strings in Byte Arrays

►Reference Data Types and Variables

 Enum Types and Enum Constants

 StringBuffer - The String Buffer Class

 System Properties and Runtime Object Methods

 Generic Classes and Parameterized Types

 Generic Methods and Type Inference

 Lambda Expressions and Method References

 Java Modules - Java Package Aggregation

 Execution Threads and Multi-Threading Java Programs

 ThreadGroup Class and "system" ThreadGroup Tree

 Synchronization Technique and Synchronized Code Blocks

 Deadlock Condition Example Programs

 Garbage Collection and the gc() Method

 Assert Statements and -ea" Option

 Annotation Statements and Declarations

 Java Related Terminologies

 Archived Tutorials

 References

 Full Version in PDF/EPUB

Reference Data Types and Variables - Updated in 2022, by Dr. Herong Yang