TABLE OF CONTENTS (HIDE)

1.  How To Install JDK on Windows
1.1  Using TextPad for Java Programming (on Windows)
1.2  Using NotePad++ for Java Programming (on Windows)
2.  How to Install JDK on Mac OS
3.  How to Install JDK on Ubuntu
4.  First Java Program with Eclipse
5.  First Java Program with NetBeans
6.  (Advanced) External JAR Files and Native Libraries

How to Install JDK 8 (on Windows, Mac OS & Ubuntu) and Get Started with Java Programming

Java Development Kit (JDK), officially named "Java Platform Standard Edition (Java SE)", which is freely available from Sun Microsystems (now part of Oracle), is needed for writing Java programs. The mother site for JDK (Java SE) is http://www.oracle.com/technetwork/java/index.html.

"JDK" or "JRE"?

JRE (Java Runtime) is needed for running Java programs. JDK (Java Development Kit), which includes JRE plus the development tools (such as compiler and debugger), is need for writing as well as running Java programs. In other words, JRE is a subset of JDK. Since you are supposed to write Java Programs, you should install JDK, which includes JRE.

JDK Versions

The various JDK versions are:

JDK Alpha and Beta (1995): Sun announced Java in September 23, 1995.
JDK 1.0 (January 23, 1996): Originally called Oak (named after the oak tree outside James Gosling's office). Renamed to Java 1 in JDK 1.0.2.
JDK 1.1 (February 19, 1997): Introduced AWT event model, inner class, JavaBean, JDBC, and RMI.
J2SE 1.2 (JDK 1.2) (December 8, 1998): Re-branded as "Java 2" and renamed JDK to J2SE (Java 2 Standard Edition). Also released J2EE (Java 2 Enterprise Edition) and J2ME (Java 2 Micro Edition). Included JFC (Java Foundation Classes - Swing, Accessibility API, Java 2D, Pluggable Look and Feel and Drag and Drop). Introduced Collection Framework and JIT compiler.
J2SE 1.3 (JDK 1.3) (May 8, 2000): Introduced Hotspot JVM.
J2SE 1.4 (JDK 1.4) (February 6, 2002): Introduced assert, non-blocking IO (nio), logging API, image IO, Java webstart, regular expression support.
J2SE 5.0 (JDK 1.5) (September 30, 2004): Officially called 5.0 instead of 1.5. Introduced generics, autoboxing/unboxing, annotation, enum, varargs, for-each loop, static import.
Java SE 6 (JDK 1.6) (December 11, 2006): Renamed J2SE to Java SE (Java Standard Edition).
Java SE 7 (JDK 1.7) (July 28, 2011): First version after Oracle purchased Sun (called Oracle JDK).
Java SE 8 (JDK 1.8) (March 18, 2014): included support for Lambda expressions, default and static methods in interfaces, improved collection, and JavaScript runtime.
Java SE 9: Expected in July 2017.

1. How To Install JDK on Windows

Step 0: Un-Install Older Version(s) of JDK/JRE

I recommend that you install only the latest JDK. Although you can install multiple versions of JDK/JRE concurrently, it is messy.

If you have previously installed older version(s) of JDK/JRE, un-install ALL of them. Goto "Control Panel" ⇒ "Programs" ⇒ "Programs and Features" ⇒ Un-install ALL programs begin with "Java", such as "Java SE Development Kit ...", "Java SE Runtime ...", "Java X Update ...", and etc.

Step 1: Download JDK

Goto Java SE download site @ http://www.oracle.com/technetwork/java/javase/downloads/index.html.
Under "Java Platform, Standard Edition" ⇒ "Java SE 8u{xx}", where {xx} is the latest update number ⇒ Click the "JDK Download" button.
Look for the latest "Java SE Development Kit 8u{xx}" ⇒ Check "Accept License Agreement".
Choose the JDK for your operating system, e.g., "Windows x64" (for 64-bit Windows OS) or "Windows x86" (for 32-bit Windows OS). You can check whether your Windows OS is 32-bit or 64-bit via "Control Panel" ⇒ (Optional) System and Security ⇒ System ⇒ Under "System Type".

Step 2: Install JDK and JRE

Run the downloaded installer (e.g., "jdk-8u{xx}-windows-x64.exe"), which installs both the JDK and JRE. By default, the JDK will be installed in directory "C:\Program Files\Java\jdk1.8.0_xx", where xx denotes the upgrade number; and JRE in "C:\Program Files\Java\jre1.8.0_xx".

Accept the defaults and follow the screen instructions to install JDK and JRE.

Check the JDK installed directory by inspecting these folders using File Explorer. Take note of your JDK installed directory, in particular, the upgrade number, which you will need in the next step.

I shall refer to the JDK installed directory as <JAVA_HOME>, hereafter, in this article.

Step 3: Include JDK's "bin" Directory in the PATH

Windows Shell searches the current directory and the directories listed in the PATH environment variable (system variable) for executable programs. JDK's programs (such as Java compiler javac.exe and Java runtime java.exe) reside in directory "<JAVA_HOME>\bin" (where <JAVA_HOME> denotes the JDK installed directory). You need to include "<JAVA_HOME>\bin" in the PATH to run the JDK programs.

To edit the PATH environment variable in Windows 7/8/10:

Launch "Control Panel" ⇒ (Optional) System and Security ⇒ System ⇒ Click "Advanced system settings" on the left pane.
Switch to "Advanced" tab ⇒ Push "Environment Variables" button.
Under "System Variables" (the bottom pane), scroll down to select "Path" ⇒ Click "Edit...".
For Windows 10 (newer releases):
You shall see a TABLE listing all the existing PATH entries (if not, goto next step). Click "New" ⇒ Enter the JDK's binary directory "c:\Program Files\Java\jdk1.8.0_xx\bin" (Replace xx with your installation number!!!) ⇒ Select "Move Up" to move this entry all the way to the TOP.

Prior to Windows 10:
(CAUTION: Read this paragraph 3 times before doing this step! Don't push "Apply" or "OK" until you are 101% sure. There is no UNDO!!!)
(To be SAFE, copy the content of the "Variable value" to Notepad before changing it!!!)
In "Variable value" field, INSERT "c:\Program Files\Java\jdk1.8.0_xx\bin" (Replace xx with your installation number!!!) IN FRONT of all the existing directories, followed by a semi-colon (;) which separates the JDK's binary directory from the rest of the existing directories. DO NOT DELETE any existing entries; otherwise, some existing applications may not run.
```
Variable name  : PATH
Variable value : c:\Program Files\Java\jdk1.8.0_xx\bin;[exiting entries...]
```

My Notes: Starting from JDK 1.8, the installation created a directory "c:\ProgramData\Oracle\Java\javapath" and added to the PATH. It contains only JRE executables (java.exe, javaw.exe, javaws.exe) but NOT the JDK executables (e.g., javac.exe).

Step 4: Verify the JDK Installation

Launch a CMD shell via one of the following means:

Click "Search" button ⇒ Enter "cmd" ⇒ Choose "Command Prompt", or
right-click "Start" button ⇒ run... ⇒ enter "cmd", or
(Prior to Windows 10) click "Start" button ⇒ All Programs ⇒ Accessories (or Windows System) ⇒ Command Prompt, or
(Windows 10) click "Start" button ⇒ Windows System ⇒ Command Prompt

Issue the following commands to verify your JDK installation:

Issue "path" command to list the contents of the PATH environment variable. Check to make sure that your <JAVA_HOME>\bin is listed in the PATH.
Don't type prompt>, which denotes the command prompt!!! Key in the command (highlighted) only.
```
// Display the PATH entries
prompt> path
PATH=c:\Program Files\Java\jdk1.8.0_xx\bin;[other entries...]
```

Issue the following commands to verify that JDK/JRE are properly installed and display their version:

// Display the JRE version
prompt> java -version
java version "1.8.0_xx"
Java(TM) SE Runtime Environment (build 1.8.0_xx-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.5-b02, mixed mode)
 
// Display the JDK version
prompt> javac -version
javac 1.8.0_xx

Step 5: Write a Hello-World Java Program

Create a directory to keep your works, e.g., "d:\myProject", or "c:\myProject", or any directory of your choice. Do NOT save your works in "Desktop" or "Documents" as they are hard to locate. The directory name shall not contain blank or special characters. Use meaningful but short name as it is easier to type.
Launch a programming text editor (such as TextPad, or NotePad++, or Sublime Text, or Atom). Begin with a new file and enter the following source code. Save the file as "Hello.java", under your work directory (e.g., d:\myProject).
```
/*
 * First Java program to say Hello
 */
public class Hello {   // Save as "Hello.java" under "d:\myProject"
   public static void main(String[] args) {
      System.out.println("Hello, world!");
   }
}
```

Step 6: Compile and Run the Hello-World Java Program

To compile the source code "Hello.java":

Start a CMD Shell (Click the "Start" button ⇒ "run..." ⇒ Enter "cmd").
Set the Current Drive to the drive where you saved your source file "Hello.java". For example, suppose that your source file is saved in drive "d", enter "d:" as follow:
```
prompt> d:
D:\xxx>
```
Don't enter prompt>, which denotes the command prompt.
Set the Current Working Directory to the directory that you saved your source file via the cd (Change Directory) command. For example, suppose that your source file is saved in directory "d:\myProject".
```
D:\xxx> cd \myProject
D:\myProject>
```
Issue a dir (List Directory) command to confirm that your source file is present in the current directory.
```
D:\myProject> dir
......
xx-xxx-xx  06:25 PM               277 Hello.java
......
```
Invoke the JDK compiler "javac" to compile the source code "Hello.java".
```
D:\myProject> javac Hello.java
```
The compilation is successful if the command prompt returns. Otherwise, error messages would be shown. Correct the errors in your source file and re-compile. Check "Common JDK Installation Errors", if you encounter problem compiling your program.

The output of the compilation is a Java class called "Hello.class". Issue a dir (List Directory) command again to check for the output.

D:\myProject> dir
......
xx-xxx-xx  01:53 PM               416 Hello.class
xx-xxx-xx  06:25 PM               277 Hello.java
......

To run the program, invoke the Java Runtime "java":

D:\myProject> java Hello
Hello, world!

Everything that can possibly go wrong will go wrong: Read "JDK Installation Common Errors".

Step 7: (Optional) Download JDK API Documentation, Samples and Demos

The JDK download does not include the documentation, which needs to be downloaded separately. In the past, I always insist that my students should have a local copy of JDK API Documentation. But, today, you can easily access the online copy by googling "JDK 8 Documentation".

To install JDK API documentation:

From the Java SE download page (@ http://www.oracle.com/technetwork/java/javase/downloads/index.html), under "Additional Resources", look for "Java SE 8 Documentation" ⇒ Download ⇒ Accept the license agreement ⇒ Download the zip-file (e.g., "jdk-8u{xx}-apidocs.zip" - about 85MB).
Unzip into the JDK installed directory <JAVA_HOME>. The documentation will be unzipped into "<JAVA_HOME>\docs". Browse the JDK documentation by opening "<JAVA_HOME>\docs\index.html".

You should also download the "JDK 8 Samples and Demos" from the Java SE download site.

Step 8: (For Advanced Users Only) JDK's Source Code

Source code for JDK is provided and kept in "<JAVA_HOME>\src.zip". I strongly recommend that you to go through some of the source files such as "String.java", "Math.java", and "Integer.java", under "java\lang".

1.1 Using TextPad for Java Programming (on Windows)

TextPad (@ www.textpad.com) is a lightweight programming text editor for writing toy Java programs. It can be configured to couple with the JDK, hence, bypassing the CMD shell.

From the TextPad editor, you can invoke the JDK compiler/runtime directly via "Tools" menu ⇒ External Tools ⇒ "Compile Java" or "Run Java Application". Take note of the keyboard shortcuts - Ctrl+1 for compile and Ctrl+2 for run.

If you cannot find these commands in the "Tools" menu, goto "Configure" ⇒ Preferences... ⇒ Tools ⇒ Add ⇒ JDK Commands.

TextPad Tips and Configuration

Check HERE!

1.2 Using NotePad++ for Java Programming (on Windows)

Notepad++ (@ http://notepad-plus-plus.org) is a free and open-source programming editor.

You can use NotePad++ to write your Java source code. But you need to use CMD shell to compile and run the Java program.

NotePad++ Customization and Tips

You can customize Notepad++ to compile and run Java programs with hot-keys. Read "NotePad++".

2. How to Install JDK on Mac OS

Step 1: Check if JDK has been Pre-Installed

In some Mac systems (earlier than Mac OS X 10.7 Lion), JDK has been pre-installed. To check if JDK has been installed, open a "Terminal" (Search "Terminal"; or Finder ⇒ Go ⇒ Utilities ⇒ Terminal) and issue this command:

javac -version

If a JDK version number is returned (e.g., JDK 1.x.x), then JDK has already been installed. If the JDK version is prior to 1.7, proceed to Step 2 to install the latest JDK; otherwise, proceed to "Step 3: Write a Hello-world Java program".
If message "command not found" appears, JDK is NOT installed. Proceed to the "Step 2: Install JDK".
If message "To open javac, you need a Java runtime" appears, select "Install" and follow the instructions to install JDK. Then, proceed to "Step 3: Write a Hello-world Java program".

Step 2: Download JDK

Goto Java SE download site @ http://www.oracle.com/technetwork/java/javase/downloads/index.html. Under "Java Platform, Standard Edition" ⇒ "Java SE 8u{xx}" ⇒ Click the "JDK Download" button
Check "Accept License Agreement"
Choose your operating platform, e.g., "Mac OS X" (jdk-8u{xx}-macosx-x64.dmg). Download the installer.

Step 3: Install JDK/JRE

Double-click the downloaded Disk Image (DMG) file. Follow the screen instructions to install JDK/JRE.
Eject the DMG file.

To verify your installation, open a "Terminal" and issue these commands.

// Display the JDK version
javac -version
javac 1.x.x_xx
 
// Display the JRE version
java -version
java version "1.x.x_xx"
Java(TM) SE Runtime Environment (build 1.x.x_xx-xxx)
Java HotSpot(TM) Client VM (build 22.1-b02, mixed mode, sharing)
 
// Display the location of Java Compiler
which javac
/usr/bin/javac
 
// Display the location of Java Runtime
which java
/usr/bin/java

Step 3: Write a Hello-World Java Program

Create a directory called "myProject" under your home directory (Launch "Finder" ⇒ "Go" ⇒ "Home"; Select "File" ⇒ "New Folder" ⇒ "myProject").
In Mac OS, the home directory of the current login user is denoted as "~". Hence, this new directory is represented as "~/myProject".
Use a programming text editor (such as jEdit, gedit, Sublime Text, or Atom) to input the following source code and save as "Hello.java" under the directory "~/myProject".
[If you use Mac OS's default text editor "TextEdit" (NOT recommended), you need to open a new file ⇒ choose "Format" ⇒ "Make Plain Text" ⇒ Enter the source code ⇒ Save as "Hello.java".]
```
/*
 * My First Java program to say Hello
 */
public class Hello {   // Save as "Hello.java" under "~/myProject"
   public static void main(String[] args) {
      System.out.println("Hello, world from Mac!");
   }
}
```

Step 4: Compile and Run the Hello-World Java Program

To compile the source code "Hello.java", open a new "Terminal" ("Go" ⇒ "Utilities" ⇒ "Terminal") and issue these commands (as illustrated):

// Change Directory (cd) to where "Hello.java" resides
cd ~/myProject
 
// Check if "Hello.java" exists using list (ls) command
ls
Hello.java   ......
 
// Compile "Hello.java" using JDK compiler "javac"
javac Hello.java
// If error message appears, correct your source code and re-compile
 
// Check for the compiled output "Hello.class"
ls
Hello.class   Hello.java   ......

To run the Hello-world, invoke the Java Runtime "java" as follows:
```
// Run "Hello.class"
java Hello
Hello, world from Mac!
```

3. How to Install JDK on Ubuntu

There are several JDK implementations available for Linux, such as Oracle JDK, OpenJDK, Sun JDK, IBM JDK and GNU Java Compiler. We shall choose the Oracle JDK 8. Ubuntu chooses OpenJDK as its default JDK, which is not 100% compatible with Oracle JDK.

Step 0: Check if JDK has already been Installed

Open a Terminal and issue this command:

$ javac -version

If a JDK version number (e.g., "javac 1.x.x_xx") appears, JDK has already been installed. You can skip the installation and goto step 2.

To remove OpenJDK, issue command:

$ sudo apt-get purge openjdk-\*

Step 1: Download and Install JDK

Goto JDK (Java SE) download site @ http://www.oracle.com/technetwork/java/javase/downloads/index.html. Under "Java Platform, Standard Edition" ⇒ "Java SE 8u{xx}" ⇒ Click "JDK Download" ⇒ Under "Java SE Development Kit 8u{xx}" ⇒ Accept License Agreement ⇒ Select "Linux x86" (for 32-bit system) or "Linux x64" (for 64-bit system) "tar.gz" package, e.g., "jdk-8u{xx}-linux-i586.tar.gz". (To check your OS version, goto "Settings" ⇒ "Details".)
The tarball will be downloaded in directory "~/Downloads", by default.
We shall install JDK under "/usr/local/java" (or Ubuntu's default JDK directory /usr/lib/jvm; or /opt/java). First, create a directory "java" under "/usr/local". Open a Terminal and issue these commands:
```
$ cd /usr/local
$ sudo mkdir java
```
Extract the downloaded package (Check your downloaded filename!)
```
$ cd /usr/local/java
$ sudo tar xzvf ~/Downloads/jdk-8u{xx}-linux-x64.tar.gz
       // x: extract, z: for unzipping gz, v: verbose, f: filename
```
JDK shall be extracted in a folder "/usr/local/java/jdk1.8.0_{xx}", where {xx} is the upgrade number.

Inform the Ubuntu to use this JDK/JRE:

// Setup the location of java, javac and javaws
$ sudo update-alternatives --install "/usr/bin/java" "java" "/usr/local/java/jdk1.8.0_{xx}/jre/bin/java" 1
      // --install symlink name path priority
$ sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/local/java/jdk1.8.0_{xx}/bin/javac" 1
$ sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/local/java/jdk1.8.0_{xx}/jre/bin/javaws" 1
 
// Use this Oracle JDK/JRE as the default
$ sudo update-alternatives --set java /usr/local/java/jdk1.8.0_{xx}/jre/bin/java
      // --set name path
$ sudo update-alternatives --set javac /usr/local/java/jdk1.8.0_{xx}/bin/javac
$ sudo update-alternatives --set javaws /usr/local/java/jdk1.8.0_{xx}/jre/bin/javaws

The above steps set up symlinks java, javac, javaws at /usr/bin (which is in the PATH), that link to /etc/alternatives and then to JDK bin directory.
The "alternatives" system aims to resolve the situation where several programs fulfilling the same function (e.g., different version of JDKs). It sets up symlinks thru /etc/alternatives to refer to the actual programs to be used.

$ ls -ld /usr/bin/java*
lrwxrwxrwx 1 root root 22 Mar 31 20:41 /usr/bin/java -> /etc/alternatives/java
lrwxrwxrwx 1 root root 23 Mar 31 20:42 /usr/bin/javac -> /etc/alternatives/javac
lrwxrwxrwx 1 root root 24 Mar 31 20:42 /usr/bin/javaws -> /etc/alternatives/javaws
 
$ ls -ld /etc/alternatives/java*
lrwxrwxrwx 1 root root 40 Aug 29 18:18 /etc/alternatives/java -> /usr/local/java/jdk1.8.0_xx/jre/bin/java
lrwxrwxrwx 1 root root 37 Aug 29 18:18 /etc/alternatives/javac -> /usr/local/java/jdk1.8.0_xx/bin/javac
lrwxrwxrwx 1 root root 42 Aug 29 18:19 /etc/alternatives/javaws -> /usr/local/java/jdk1.8.0_xx/jre/bin/javaws

Alternatively, you can include the JDK's bin and JRE's bin into the PATH directly.

To verify the JDK installation, issue these commands:

// Show the Java Compiler (javac) version
$ javac -version
javac 1.8.0_xx
 
// Show the Java Runtime (java) version
$ java -version
java version "1.8.0_xx"
Java(TM) SE Runtime Environment (build 1.8.0_xx-xxx)
Java HotSpot(TM) 64-Bit Server VM (build 25.xx-xxx, mixed mode)
 
// Show the location of javac and java
$ which javac
/usr/bin/javac
$ which java
/usr/bin/java

(Optional) To use Java under Firefox, you need to enable the so-called "Java Plugin for web browser".
```
$ cd ~/.mozilla/plugins
// if this directory does not exist, create it
$ mkdir ~/.mozilla/plugins
```
Then, create a symbolic link to your Mozilla plugins folder, (check your JDK folder)
```
$ cd ~/.mozilla/plugins
$ sudo ln -s /usr/local/java/jdk1.8.0_{xx}/jre/lib/amd64/libnpjp2.so
```
To verify the installation, restart your Firefox and issue URL "about:plugins". Check for Java plugins with the correct version.
Starting from JDK 1.8, to run unsigned applets, you need to set security level to "high" add the sites to the "Exception List" (under the Java Control Panel ⇒ Security). To start the Java Control Panel:
```
$ cd /usr/local/java/jdk1.8.0_{xx}/jre/bin
$ ./ControlPanel      // OR ./jcontrol
```
You need to restart Firefox after modifying the Exception List.

[Don't Do this step - It is taken care by "alternative" in Step 3. Keep here to show you how to set PATH.]
Add JDK's binary directory ("bin") to the "PATH" by editing "/etc/profile":

$ cd /etc
$ gksudo gedit profile   // OR "sudo nano profile" to use the console-based nano editor

Add these lines at the end of the file "/etc/profile", replace "{xx}" with the actual number:

export JAVA_HOME=/usr/local/java/jdk1.8.0_{xx}
export PATH=$JAVA_HOME/bin:$PATH

Rerun the configuration file by:

// Refresh
$ source /etc/profile
 
// Check the new settings for JAVA_HOME and PATH
$ echo $JAVA_HOME
/usr/local/java/jdk1.8.0_{xx}
 
$ echo $PATH
.....:/usr/local/java/jdk1.8.0_{xx}/bin

Step 2: Compile and Run a Hello-world Java Program

File Explorer ⇒ Home ⇒ Create a new folder called "myProject" to keep our works.

Open "Text Editor" (gedit). Enter the following source code and save as "Hello.java" under the "~/myProject" directory created earlier.

public class Hello {   // To save as "Hello.java" under "~/myProject"
   public static void main(String[] args) {
      System.out.println("Hello, world from Ubuntu!");
   }
}

To compile the Hello-world Java program, launch a Terminal and issue these commands:

// Change directory to where the source code resides
$ cd ~/myProject
 
// List the contents of current directory. Check for "Hello.java"
$ ls
...... Hello.java ....
 
// Compile "Hello.java" into "Hello.class"
$ javac Hello.java
 
// Check for "Hello.class"
$ ls
...... Hello.class ....

Run the Hello-world Java program:

// Run "Hello.class"
$ java Hello
Hello, world from Ubuntu!

4. First Java Program with Eclipse

You need to first install Eclipse. Read "How to Install Eclipse".
You can then proceed to write your first Java program. Read "Writing your first Java Program with Eclipse".
Eclipse allow you to debug program graphically. Read "Debugging program in Eclipse".

5. First Java Program with NetBeans

You need to first install NetBeans. Read "How to Install NetBeans".
You can then proceed to write your first Java program. Read "Writing your first Java program with NetBeans".
NetBeans allow you to debug program graphically. Read "Debugging program in NetBeans".

6. (Advanced) External JAR Files and Native Libraries

External Java packages (such as Servlet, MySQL Connector/J, JOGL, JUnit) are often distributed in JAR files (Java Archive - a single-file package of many Java classes), with possibly Native Libraries (".lib" and ".dll" in Windows, or ".a" and ".so" in Linux/Mac).

External JAR Files (".jar")

If external JAR files are not properly included:

During the compilation, you will receive compilation error "cannot find symbol" on classes belonging to the external packages.
During execution, you will get a runtime error "Could not find or load main class xxx" or "NoClassDefFoundError".

To include external JAR files, you can either:

Copy all the JAR files of the external packages to the Java's Extension Directories.
- For Windows, the JDK extension directory is located at "<JAVA_HOME>\jre\lib\ext" (e.g., "c:\Program Files\Java\jdk1.8.0_xx\jre\lib\ext").
- For Mac, the JDK extension directories are "/Library/Java/Extensions" and "/System/Library/Java/Extensions".
- For Ubuntu, the JDK extension directories are "<JAVA_HOME>/jre/lib/ext" (e.g., "/usr/user/java/jdk1.8.0_xx/jre/lib/ext") and "/usr/java/packages/lib/ext".
The location of JDK's extension directories is kept in Java's System Property "java.ext.dirs". You can print its contents via System.out.println(System.getProperty("java.ext.dirs")).
You can also include all the JAR files in the CLASSPATH environment variable. CLASSPATH may contain directories (of Java classes) or JAR files (single-file archive of Java classes). If you set the CLASSPATH, you must also include the current directory (denoted as ".").
- For Windows, set the CLASSPATH in Control Panel ⇒ System ⇒ Advanced system settings ⇒ Advanced ⇒ Environment Variables ⇒ System Variables ⇒ New ⇒ In "Variable name", enter "CLASSPATH" ⇒ In "Variable value", enter ".;path1\xxx.jar;path2\yyy.jar", where the entries are separated by a semi-colon (;).
- For Linux and Mac OS: Edit ~/.profile or ~/.bash_profile (or /etc/profile for system-wide setting) to include the following line at the end of the file:
```
export CLASSPATH=.:path1/xxx.jar:path2/yyy.jar
```
  The entries are separated by colon (:).

You can also set the CLASSPATH in the javac/java command-line via the option -cp <paths> (or -classpath <paths>), for example,

// Compile Java source code
> javac -cp .:path1/xxx.jar:path2/yyy.jar ClassName.java
// Run Java class
> java -cp .:path1/xxx.jar:path2/yyy.jar ClassName

External Native Libraries (".lib", ".dll", ".a", ".so")

Some external package may provide static or shared native libraries in the form of ".lib" (Windows' static library), ".dll" (Windows' dynamically link library), ".a" (Unix's static library), or ".so" (Unix's shared library).

Native Libraries are to be kept in a directory accessible via JRE's Property "java.library.path", which normally but not necessarily includes all the directories in the PATH environment variable.

Native libraries are not involved in the compilation. But if they are not properly included during runtime time, you will get a runtime error "java.lang.UnsatisfiedLinkError: no xxx in java.library.path".

To include external native libraries:

Copy the native libraries into a system library directory, e.g., c:\windows\system32 (Windows), /usr/lib or /usr/local/lib (Linux or Mac OS). You can verify that the directory is included in Java's System Property "java.library.path", via System.out.println(System.getProperty("java.library.path")).
You can also set the native library path via the java's command-line option -Djava.library.path=xxx, for example,
```
> java -Djava.library.path=xxx ClassName
```

Eclipse/NetBeans

Using an IDE can greatly simplifies inclusion of external packages. Read "Eclipse How-To" or "NetBeans How-To".

Link to References & Resources

Latest version tested: JDK 1.8.0_112
Last modified: January, 2017