Java Tutorials - Herong's Tutorial Examples

Java Tutorials

- Herong's Tutorial Examples

v8.22, 2024

Herong Yang

Copyright © 1997-2024 Herong Yang. All rights reserved.

ISBN: 978-0-359-43966-9

This tutorial book is a collection of notes and sample codes written by the author while he was learning Java himself. Topics covered in the book include: Java language basics; execution environment; generic classes and parameterized type; generic methods and type argument inferences; enum types and constants; lambda expressions; annotation types and invocations; Java modules; execution threads and synchronization; memory management and garbage collection. Updated in 2024 (Version v8.22) with JDK 20.

Table of Contents

About This Book

JDK - Java Development Kit

Downloading and Installing JDK on Mac

Downloading and Installing JDK on Windows

Adding JDK bin Directory to Path Setting

Downloading and Installing JDK on Linux

Writing My First Java Program

JDK Documentation Installation

Execution Process, Entry Point, Input and Output

Creating, Compiling and Executing Java Programs

main() Method - Java Execution Entry Point

Java Execution Console - in, out and err Data Streams

Primitive Data Types and Literals

Data Types Supported in Java

Integer Data Types

Floating-Point Data Types

Logical (Boolean) Data Type

Literals of Primitive Types

Literal Formats for Integers

Literal Formats for Integers - Example

Literal Formats for Floating-Point

Literal Formats for Floating-Point - Example

Literal Formats for Characters

Literal Formats for Character - Example

Control Flow Statements

What Is Control Flow Statement

if-then Statements

if-then-else Statements

Nested if-then-else Statements

switch Statements

Fall-Through Behavior of switch Statements

Basic for Statements

Enhanced for Statements

while Statements

do Statements

break Statements

Labeled break Statements

continue Statements

Labeled continue Statements

Bits, Bytes, Bitwise and Shift Operations

What Are Bits and Bytes

byte Data Type and Implicit Casting

Operations on byte Data Type Values

Bitwise Operations on byte Values

Bitwise Operations on byte Values - Example Program

Shift Operations - Left, Right or Unsigned Right

Managing Bit Strings in Byte Arrays

setBit() - Storing a Bit into a Byte Array

getBit() - Retrieving a Bit from a Byte Array

rotateLeft() - Left Rotating All Bits in a Byte Array

bitStringTest.java - Testing Program

Reference Data Types and Variables

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

Enum Types and Enum Constants

What Is an Enum Type

Use 'class' to Define Enumeration

Instance Variables for Enum Constants

java.lang.Enum Super Type

Enum Constant Inherited Methods

Enum Constant Implicit Methods

StringBuffer - The String Buffer Class

StringBuffer Class Properties and Methods

SimpleStringBuffer - My Implementation of String Buffer

Performance Comparison of String and StringBuffer

System Properties and Runtime Object Methods

JVM and OS System Properties

System.setProperty() - Setting Your Own Properties

Runtime.getRuntime() - Getting the Runtime Object

freeMemory() - Getting JVM Free Memory Information

Calculating Memory Usage of an Array

exec() - Executing Operating System Commands

Generic Classes and Parameterized Types

What Is a Generic Class

Using a Generic Class

Using a Generic Class - Example

Creating a Generic Class

Creating a Generic Class - Example

Bounded Type Parameters

Raw Type, Generic Type and Parameterized Type

Parameterized Type and Subtyping

Wildcard Parameterized Types

Wildcard Parameterized Type Test

Wildcard Parameterized Subtyping

Wildcard Parameterized Subtyping Example

Generic Methods and Type Inference

What Is a Generic Method

Comparing Generic Method with Non-Generic Method

Non-Generic Method Example - maxNonGeneric()

Generic Method Example - maxGeneric()

Generic Methods in java.util.Collections Class

Testing Generic Methods in Collections Class

What Is Type Argument Inference

Type Argument Inference by Parameter List

Type Argument Inference by Return Value

Generic Methods using Parameterized Types

Parameterized Type as Generic Method Return Type

Lambda Expressions and Method References

What Is Lambda Expression

LambdaCalculator.java - Lambda Expression Example

Lambda Expression Syntax Options

Lambda Expression as Method Reference

Method Reference Example - LambdaMethodRefernce.java

Lambda Expression Stream Pipeline Operations

Java Modules - Java Package Aggregationxhtml

What Is Java Module

Module Descriptor - module-info.java

Creating Hello World! Module

jmod create - Creating JMOD File

jlink --add-modules - Creating Custom JRE

Running .\bin\java Command in Custom JRE

Accessing Non-Exported Package in Module

Module Dependency and Package Accessibility

com.herongyang.base Module Implementation

com.herongyang.base Module Compilation

com.herongyang.math Module Implementation

geometryJRE and Module Deliverables

Getting com.herongyang.base Module Info

Testing Exported Package in Module

Testing Un-Exported Package in Module

Application using com.herongyang.math Module

Execution Threads and Multi-Threading Java Programs

What Are Processes and Threads

The Thread Class - Creating Thread Objects With Thread Sub Classes

The Runnable Interface - Creating Thread Objects with Runnable Objects

CPU Execution Time Shared by Multiple Threads

CPU Execution Time Shared by Multiple Threads - Test Output

Application Data Shared by Multiple Threads

Application Data Shared by Multiple Threads - Test Results

interrupt() - Method to Terminate Thread

ThreadGroup Class and system ThreadGroup Tree

ThreadGroup Class - Container of Threads and Thread Groups

Displaying the system ThreadGroup Tree

Adding Threads and Thread Groups

Synchronization Technique and Synchronized Code Blocks

Why Synchronization Is Needed in Multi-Threading Applications

Synchronization Technique - Lock and Synchronized Code

synchronized - How Java Supports Synchronization

BankingThread.java - Synchronization Sample Program

BankingThread.java - Synchronization Sample Program Output

Deadlock Condition Example Programs

What Is Deadlock

Deadlock Example - 5 Dining Philosophers

Deadlock Example - Transferring Funds

Garbage Collection and the gc() Method

Garbage Collection and Unused Objects

The Automated Garbage Collection Process

gc() - The Garbage Collection Method

Example Program of Using the gc() Method

Assert Statements and -ea" Optionxhtml

assert Statements

JVM -ea and -da Options

Annotation Statements and Declarationsxhtml

What Is Annotation

Use interface as Annotation

Default Values for Annotation Elements

Single-Element Annotation Invocation

No-Element (Marker) Annotation Invocation

getAnnotations() Method - Annotation APIs

Predefined Annotation Types

Java Related Terminologies

Archived Tutorials

Archived: Downloading and Installing JDK 13 on Mac

Archived: Downloading and Installing JDK 10

Archived: JDK 10 Documentation Installation

Archived: Downloading and Installing JDK 8

Archived: Downloading and Installing JDK 1.7

Archived: Downloading and Installing JDK 1.6

Archived: Downloading and Installing JDK 1.5

Archived: JDK 1.3 Bug - Memory Leak With Unstarted Threads

References

Keywords: Java, Language, Tutorial

Java Tutorials - Herong's Tutorial Examples

∟ About This Book

This section provides some detailed information about this book - Java Tutorials - Herong's Tutorial Examples.

Title: Java Tutorials - Herong's Tutorial Examples

Author: Herong Yang - Contact by email via herong_yang@yahoo.com.

Category: COMPUTERS / Programming Languages / Java

Version/Edition: v8.22, 2024

Number of pages in PDF format: 345

Description: This tutorial book is a collection of notes and sample codes written by the author while he was learning Java himself. Topics covered in the book include: Java language basics; execution environment; generic classes and parameterized type; generic methods and type argument inferences; enum types and constants; lambda expressions; annotation types and invocations; Java modules; execution threads and synchronization; memory management and garbage collection. Updated in 2024 (Version v8.22) with Java 20.

Keywords: Java, variable, type, expression, statement, method, class, package, module, thread, deadlock.

Cost/Price: Free in Web format

Copyright:

This book is under Copyright © 1997-2024 Herong Yang. All rights reserved.

Material in this book may not be published, broadcasted, rewritten or redistributed in any form.

The example codes is provided as-is, with no warranty of any kind.

Revision history:

Version v8.22, 2024. Updated with Java 20.

Version v8.10, 2018. Added Java Module tutorials.

Version v8.00, 2018. Updated with Java 10.

Version v7.00, 2014. Updated with Java 8.

Web version: https://www.herongyang.com/Java - Provides free sample chapters, latest updates and readers' comments. The Web version of this book has been viewed a total of:

1,843,942 times as of December 2023.

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PDF/EPUB version: https://www.herongyang.com/Java/PDF-Full-Version.html - Provides information on how to obtain the full version of this book in PDF, EPUB, or other format.

Java Tutorials - Herong's Tutorial Examples

∟ JDK - Java Development Kit

This chapter provides tutorial notes on installing JDK on your own Windows system to run Java programs. Topics include downloading and installing JDK; compiling and executing Java programs, installing JDK documentation.

Downloading and Installing JDK on Mac

Downloading and Installing JDK on Windows

Adding JDK bin Directory to Path Setting

Downloading and Installing JDK on Linux

Writing My First Java Program

JDK Documentation Installation

Takeaways:

Downloading and installing JDK on Windows, Mac, or Linux computers is easy and fast.

Compiling and running the first Java program requires 2 commands: javac and java.

Java Tutorials - Herong's Tutorial Examples

∟ JDK - Java Development Kit

∟ Downloading and Installing JDK on Mac

This section describes how to download and install JDK 13 on a Mac computer

To learn Java, you need to have a copy of JDK (Java Development Kit) installed on your machine. If you are a Mac computer user, you can follow this tutorial to download and install JDK 20 on your Mac computer.

1. Go to Oracle Java SE download website at oracle.com/technetwork/java/javase/downloads.

2. Click JDK 20 > macOS tab.

3. Click on the jdk-20_macos-x64_bin.dmg link in the x64 DMG Installer line to download the installation file to your Downloads directory.

4. Double-click on the jdk-20_macos-x64_bin.dmg file to install it.

To test the installation, open a command window to try the java command.

herong$ java -version

java version 20.0.1 2023-04-18

Java(TM) SE Runtime Environment (build 20.0.1+9-29)

Java HotSpot(TM) 64-Bit Server VM (build 20.0.1+9-29, mixed mode, sharing)

Cool, I have successfully installed JDK 20 on my macOS computer!

Java Tutorials - Herong's Tutorial Examples

∟ JDK - Java Development Kit

∟ Downloading and Installing JDK on Windows

This section describes how to download and install JDK on a Windows system.

To learn Java, you need to have JDK installed on your computer. If you are Windows user, you can follow what I did to download and install JDK 17 on your Windows computer.

1. Open the Java SE Download page with this URL: https://www.oracle.com/java/technologies/downloads/.

2. Click the Windows tab under the Java SE Development Kit 17.0.1 downloads. You will see a new page with a list of different download files of JDK 17.

3. Click the hyper link of https://download.oracle.com/java/17/latest/jdk-17_windows-x64_bin.exe, next to x64 Installer 152 MB.

4. Save jdk-17_windows-x64_bin.exe to a temporary directory.

5. Double-click on jdk-17_windows-x64_bin.exe to start the installation wizard.

6. Follow instructions on the installation wizard to finish the installation.

The picture below shows you how the JDK 17 Installation Screen looks like:

JDK 17 Installation Screen

To test the installation, open a command window to try the java command. If you are getting the following output, your installation is good:

herong> \progra~1\java\jdk-17.0.1\bin\java -version

java version 17.0.1 2021-10-19 LTS

Java(TM) SE Runtime Environment (build 17.0.1+12-LTS-39)

Java HotSpot(TM) 64-Bit Server VM

  (build 17.0.1+12-LTS-39, mixed mode, sharing)

Congratulations, you have successfully installed JDK on your Windows computer!

Java Tutorials - Herong's Tutorial Examples

∟ JDK - Java Development Kit

∟ Adding JDK bin Directory to Path Setting

This section provides a tutorial on how to add JDK 'bin' directory to the 'path' system envirnoment variable.

In order to run Java compiler and JVM by typing their program file name without the directory path name, I updated the path environment variable on my Windows computer:

Open Control Panel > System and Security > System.

Click Advanced system settings.

Click Environment Variables.

Select System variables > Path and click Edit.

Add C:\Progra~1\java\jdk-17.0.1\bin; to the beginning of the current path list.

Click OK to save the change.

Then I ran the echo %path% command in a new command window to confirm the change:

herong> echo %path%

C:\Progra~1\java\jdk-17.0.1\bin;

  C:\Program Files\Common Files\Oracle\Java\javapath;

  C:\ProgramData\Oracle\Java\javapath;

  ...

Now I should be able to run Java commands without the directory path name:

herong> java -version

java version 17.0.1 2021-10-19 LTS

...

herong> javac hello.java

herong> java Hello

Hello world!

Now I am ready to play with Java tools included in Oracle JDK package!

Adding JDK bin Directory to Path Setting

You can also set a new environment variable called java_home to avoid typing the full path name to access Java tool program files:

herong> set java_home=C:\Progra~1\java\jdk-17.0.1

herong> %java_home%\bin\java -version

java version 17.0.1 2021-10-19 LTS

...

Java Tutorials - Herong's Tutorial Examples

∟ JDK - Java Development Kit

∟ Downloading and Installing JDK on Linux

This section provides a tutorial example on how to download and install JDK on Linux systems. The best way to install JDK on CentOS system is to the 'yum' package management tool.

Downloading and installing JDK on a Linux computer is more difficult for several reasons:

1. There are many variations and versions of Linux platforms running on different system architectures. So there is no single JDK package that works perfectly on all Linux platforms.

2. Oracle offers 3 binary packages for all Linux platforms with some installation instructions:

Package                    Platforms

-------                    -------

Linux Debian Package      Debian

Linux RPM Package          Red Hat and SuSE

Linux Compressed Archive  Generic

3. OpenJDK offers a single generic binary package for all Linux platforms.

If you try to install the generic binary package on your specific Linux platform, you most likely will encounter some issues.

The best way to install JDK on your specific Linux platform is to use the package management tool on the system to search and automatically install the OpenJDK binary package that was built specifically for your platform.

Here is what did to on my CentOS system with the yum package management tool to search for openJDK, logging in as root:

herong# yum search openJDK

java-1.6.0-openjdk.i686 : OpenJDK Runtime Environment

java-1.6.0-openjdk-devel.i686 : OpenJDK Development Environment

java-1.6.0-openjdk-javadoc.i686 : OpenJDK API Documentation

java-1.6.0-openjdk-src.i686 : OpenJDK Source Bundle

...

java-1.8.0-openjdk.i686 : OpenJDK Runtime Environment

java-1.8.0-openjdk-devel.i686 : OpenJDK Development Environment

java-1.8.0-openjdk-javadoc.noarch : OpenJDK API Documentation

java-1.8.0-openjdk-src.i686 : OpenJDK Source Bundle

So the latest version for my platform is OpenJDK 1.8, divided into several parts. To install JDK with compiler and other tools, I need to install java-1.8.0-openjdk.i686 and java-1.8.0-openjdk-devel.i686:

herong# yum install java-1.8.0-openjdk

...

Installed:

  java-1.8.0-openjdk.i686 1:1.8.0.232.b09-1.el6_10

herong# yum install java-1.8.0-openjdk

...

Installed:

  java-1.8.0-openjdk-devel.i686 1:1.8.0.232.b09-1.el6_10

Now verify the installation:

herong# java -version

openjdk version 1.8.0_232

OpenJDK Runtime Environment (build 1.8.0_232-b09)

OpenJDK Server VM (build 25.232-b09, mixed mode)

herong# javac -version

javac 1.8.0_232

Finally, set the JAVA_HOME environment variable, so other applications can find where JDK is installed. This can be done with an export command.

herong# export JAVA_HOME=/usr/lib/jvm/jre-1.8.0-openjdk.i386

Congratulations, you have successfully installed JDK on your Linux system!

Java Tutorials - Herong's Tutorial Examples

∟ JDK - Java Development Kit

∟ Writing My First Java Program

This section provides a tutorial example on how to write, compile, and execute the first Java program with JDK.

When JDK is installed on your machine, it provides two commands for you to compile and run Java programs.

javac class_name.java - Compiles a Java program stored a file named with the program class name.

java -classpath . class_name - Runs a compiled Java program. -classpath . specifies the current directory as the class path.

Let's try these commands with a very simple Java program. Use NotePad to enter the following Java program into a file called Hello.java:

class Hello {

  public static void main(String[] a) {

      System.out.println(Hello world!);

  }

}

Then compile this program in a command window with the javac command:

herong> javac Hello.java

To execute the program, use the java command:

herong> java Hello

Hello world!

Congratulations, you have successfully entered, compiled and executed your first Java program.

Java Tutorials - Herong's Tutorial Examples

∟ JDK - Java Development Kit

∟ JDK Documentation Installation

This section describes how to install JDK Documentation on your own local machine.

To learn Java more effectively, you definitely need to have a copy of the JDK Documentation installed on your computer. JDK Documentation provides you detailed information of all classes and methods used in JDK.

You can follow what I did to download and install JDK 17 Documentation.

1. Open the Java download home page with this URL: https://www.oracle.com/java/technologies/downloads/.

2. Click the Documentation Download button near the bottom of the page. You will see Java SE Development Kit 17 Documentation page showing up.

3. Click the hyper link of jdk-17.0.1_doc-all.zip.

4. Save the download file jdk-17.0.1_doc-all.zip to a temporary directory.

5. Double-click on jdk-17.0.1_doc-all.zip to extract all files to "C:\Program Files\Java\jdk-17.0.1 directory.

6. To verify the installation, open the C:\Program Files\Java\jdk-17.0.1\docs\index.html with a Web browser. You should see the JDK 17 Documentation starting page.

7. Click the java.logging module on the JDK 17 Documentation page to see the API documentation of the java.logging module.

If you are a Mac user, you need to extract all files from jdk-17.0.1_doc-all.zip to /Library/Java/JavaVirtualMachines/jdk-17.jdk directory. And open docs/index.html from that directory in a Web browser.

If you are a Linux user, you can extract all files from jdk-17.0.1_doc-all.zip to the ~/jdk directory. And open docs/index.html from that directory in a Web browser.

Java Tutorials - Herong's Tutorial Examples

∟ Execution Process, Entry Point, Input and Output

This chapter provides tutorial notes and tutorial examples on Java program execution process. Topics include Java program creation, compilation and execution; the main() method - execution entry point; execution console, input and output data streams.

Creating, Compiling and Executing Java Programs

main() Method - Java Execution Entry Point

Java Execution Console - in, out and err Data Streams

Takeaways:

3 steps are involved in building a Java application: creating source code, compiling source code and executing the compiled code.

public static void main(String[] a) is the execution entry point when a class is launched in the Java Virtual Machine (JVM).

JVM provided 3 default I/O data streams to all applications: in, out and err.

Java Tutorials - Herong's Tutorial Examples

∟ Execution Process, Entry Point, Input and Output

∟ Creating, Compiling and Executing Java Programs

This section describes the process of Java program creation, compilation and execution. JDK 'javac' and 'java' commands are also described.

There are 3 steps involved in building and running a Java program:

Creating Program Source Code: Creating one text file written Java language statements to define each Java class or other program unit. The text file is called source code file, which must have a file name identical to the name of the class defined in the file, and an extension of .java. One of the source code files should define the main class which contains the main method as the execution starting point. Other source code files define additional classes and other program units to support the main class.

Compiling Source Code: Converting all source code files of the program into bytecode files written in Java Virtual Machine (JVM) instructions. The bytecode file must have the same file name as the source code file, and an extension of .class.

Executing the Java Program: Loading the bytecode file of the main class into JVM, and executing its JVM instructions starting from the main method.

Creating a source code file can be done by a simple text editor, notepad, or a sophisticated Java development environment tool, like Eclipse, or Visual J++.

Compiling a source code file needs a Java compiler. The JDK package contains a Java compiler, which can be invoked by the command javac. The javac command takes source code file names as command line arguments. For example, entering the following command in command window will invoke the javac compiler to compile the Hello.java source code file:

herong> javac Hello.java

The javac command also has several command options available:

-d: Specify the directory where the bytecode files generated by the compiler should be placed, if you don't want to place them in the current directory.

-classpath: Specify the directories where to search for classes or interfaces definitions in bytecode format, if the classes or interfaces are used in source code file.

-sourcepatch: Specify the directories where to search for classes or interfaces definitions in source code format, if the classes or interfaces are used in source code file.

For example, the following command:

herong> javac -d .\cls -classpath .\lib;.\cls \

  -sourcepath .\src .\src\Hello.java

invokes the javac compiler, and tells it to:

Compile the Hello.java source code file in the .\src directory.

Place the bytecode file, Hello.class, in the .\cls directory.

Search .\lib and .\cls directories for the definitions in bytecode format of classes or interfaces that are used in Hello.java.

Search .\src directory for the definitions in source code format of classes or interfaces that are used in Hello.java.

Executing a Java program needs a JVM. The JDK also contains a JVM, called HotSpot, which can be invoked by the command java. The java command takes the name of the starting class as the command argument. For example, the following command:

herong> java -classpath .\lib;.\cls;. Hello

invokes HotSpot to:

Load Hello class into HotSpot.

Execute the main() method of the Hello class.

The -classpath option specifies the class path, which contains directories where the JVM will search for the bytecode files of the starting class and other program units when needed.

Java Tutorials - Herong's Tutorial Examples

∟ Execution Process, Entry Point, Input and Output

∟ main() Method - Java Execution Entry Point

This section describes the Java program entry point, the main() method of the starting class. Command line arguments are passed as an string array parameter to the main() method.

As mentioned in the previous section, a Java application program must have a main class with a special method call main() as the execution entry point. The main() method must be defined as:

  public static void main(String[] a) {

      // statement block

  }

Note that the main() method must be declared as public static void.

The parameter of the main() method is an array of String, which contains the additional arguments after the class name argument in the java command line. Let's use the following Java program to illustrate how those arguments are passed into the main() method: