The Java Development Kit (JDK), officially named 'Java Platform Standard Edition' or 'Java SE', is needed for writing Java programs. The JDK is freely available from Sun Microsystems (now part of Oracle). The mother site for JDK (Java SE) is http://www.oracle.com/technetwork/java/javase/overview/index.html.
Liberica JDK provides Long term Support for all of its open source builds that act as alternatives for Java application development toolkits. The Liberica OpenJDK package with the HotSpot Virtual Machine viably replaces the Java 8 (LTS), 9, 10, 11 (LTS), 12, 13, 14, 15. I have installed the jre-8u121-macosx8.0.1210.13.dmg When I install my downloaded jdk(jdk-8u121-macosx-x64), there comes an issue: jdk-8u121-macosx-x64 image not recognized.
Ubuntu: Java JDK 6; Mac OS X: Java JDK 6; Android 1.5 (Cupcake) – Android 2.2.x (Froyo): Ubuntu: Java JDK 5; JDK for Linux. The master branch of Android in the Android Open Source Project (AOSP) comes with prebuilt versions of OpenJDK below prebuilts/jdk/ so no additional installation is required.
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.
Reference: 'Java Version History' @ https://en.wikipedia.org/wiki/Java_version_history.
assert
statement, non-blocking IO (nio
), logging API, image IO, Java webstart, regular expression (regex) support.switch
statement, Binary integer literals, allowing underscores in numeric literals, improved type inference for generic instance creation (or diamond operator <>
), Catching multiple exception types and rethrowing exceptions with improved type checking. See 'JDK 7 New Features'.module
) under project Jigsaw, the Java Shell (jshell
), and more. See 'JDK 9 New Features'.var
for type inference local variable (similar to JavaScript). Introduced time-based release versioning with two releases each year, in March and September, denoted as YY.M.
Removed native-header generation tool javah
. See 'JDK 10 New Features'.var
to lambda expression. Standardize HTTP client in java.net.http
. Support TLS 1.3. Clean up the JDK and the installation package (removed JavaFX, JavaEE, CORBA modules, deprecated Nashorn JavaScript engine). OracleJDK is no longer free for commercial use, but OpenJDK is still free. See 'JDK 11 New Features'.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' ⇒ (optional) '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.
jdk-13.0.{x}_windows-x64_bin.exe
' - about 159MB).Run the downloaded installer (e.g., 'jdk-13.0.{x}_windows-x64_bin.exe
'), which installs both the JDK and JRE.
By default, JDK is installed in directory 'C:Program FilesJavajdk-13.0.{x}
', where {x}
denotes the update number. Accept the defaults and follow the screen instructions to install JDK.
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Use your 'File Explorer', navigate to 'C:Program FilesJava'
to inspect the sub-directories. Take note of your JDK installed directoryjdk-13.0.{x}
, in particular, the update number {x}
, which you will need in the next step.
I shall refer to the JDK installed directory as <JAVA_HOME>
, hereafter, in this article.
Windows' Command Prompt (CMD
) searches the current directory and the directories listed in the PATH
environment variable (or system variable) for executable programs. JDK's programs (such as Java compiler 'javac.exe
' and Java runtime 'java.exe
') reside in the sub-directory 'bin
' of the JDK installed directory. You need to include JDK's 'bin
' in the PATH
to run the JDK programs.
To edit the PATH
environment variable in Windows 10:
bin
' directory, i.e., 'c:Program FilesJavajdk-13.0.{x}bin
', where {x}
is your installation update number ⇒ Select 'Move Up' to move this entry all the way to the TOP.c:Program FilesJavajdk-13.0.{x}bin
' (where {x}
is your installation update number) IN FRONT of all the existing directories, followed by a semi-colon (;
) to separate the JDK's bin directory from the rest of the existing directories. DO NOT DELETE any existing entries; otherwise, some existing applications may not run. Note: If you have started CMD, you need to re-start for the new environment settings to take effect.
Launch a CMD
via one of the following means:
Issue the following commands to verify your JDK installation:
path
' command to list the contents of the PATH
environment variable. Check to make sure that your JDK's 'bin
' is listed in the PATH
. d:myProject
' or 'c:myProject
'. 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.Hello.java
', under your work directory (e.g., d:myProject
). To compile the source code 'Hello.java
':
Hello.java
'. d
', enter 'd:
' as follow: cd
(Change Directory) command. For example, suppose that your source file is saved in directory 'myProject
'.dir
(List Directory) command to confirm that your source file is present in the current directory. javac
' to compile the source code '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.Hello.class
'. Issue a dir
(List Directory) command again to check for the output. To run the program, invoke the Java Runtime 'java
':
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Everything that can possibly go wrong will go wrong: Read 'JDK Installation Common Errors'.
Source code for JDK is provided and kept in '<JAVA_HOME>libsrc.zip
' (or '<JAVA_HOME>src.zip
' prior to JDK 9). I strongly recommend that you to go through some of the source files such as 'String.java
', 'Math.java
', and 'Integer.java
', under 'javalang
', to learn how experts program.
To check if JDK has been installed, open a 'Terminal' (Search 'Terminal'; or Finder ⇒ Go ⇒ Utilities ⇒ Terminal) and issue this command:
JDK x.x.x
), then JDK has already been installed. If the JDK version is prior to 1.8, proceed to Step 2 to install the latest JDK; otherwise, proceed to 'Step 3: Write a Hello-world Java program'.jdk-13.0.{x}_osx-x64_bin.dmg
- about 172MB).myProject
' under your home directory (Launch 'Finder' ⇒ 'Go' ⇒ 'Home'; Select 'File' ⇒ 'New Folder' ⇒ 'myProject
').~
'. Hence, this new directory can be referenced as '~/myProject
'.Hello.java
' under the directory '~/myProject
'.Hello.java
'.) Hello.java
', open a new 'Terminal' ('Go' ⇒ 'Utilities' ⇒ 'Terminal') and issue these commands (as illustrated): java
' as follows: 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.
Open a Terminal and issue this command:
If a JDK version number (e.g., 'javac x.x.x
') appears, JDK has already been installed. You can skip the installation and goto step 2.
To remove OpenJDK, issue command:
tar.gz
' package, (e.g., 'jdk-13.0.{x}-linux-x64_bin.tar.gz
' - 171MB).~/Downloads
', by default./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: Extract the downloaded package (Check your downloaded filename!) JDK shall be extracted in a folder '/usr/local/java/jdk-13.0.{x}
', where {x}
is the update number.java
, javac
, javaws
at /usr/bin
(which is in the PATH), that link to /etc/alternatives
and then to JDK bin directory./etc/alternatives
to refer to the actual programs to be used.bin
') to the 'PATH' by editing '/etc/profile
': Add these lines at the end of the file '/etc/profile
', replace '{x}
' with the actual number: Rerun the configuration file by: myProject
' to keep our works.Hello.java
' under the '~/myProject
' directory created earlier. Click HERE, look for 'VS Code for Java Programming'
Click HERE, look for 'Sublime Text for Java Programming'
[TODO]
Click HERE, look for 'TextPad for Java Programming'.
Click HERE, look for 'NotePad++ for Java Programming'.
From JDK 11, you can compile/run a single-file program in one step, without explicit compilation.
Hello.java
' (see previous section).Hello.class
', if it exists.Hello.java
' in one command as follows: Notes:
javac
to compile the program..class
file), and run.Many Java applications (such as Tomcat) require the environment variable JAVA_HOME
to be set to the JDK installed directory.
See 'How to set JAVA_HOME for Windows' or 'How to set JAVA_HOME for macOS/Linux'.
Notes: This section is applicable to JDK prior to JDK 9. JDK 9 introduces a new level called 'module' on top of package, and 'jmod
' files for Java modules. Need to revise this section for JDK 9.
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/macOS).
If external JAR files are not properly included:
NoClassDefFoundError
'.To include external JAR files, you can either:
<JAVA_HOME>jrelibext
' (e.g., 'c:Program FilesJavajdk1.8.0_xxjrelibext
')./Library/Java/Extensions
' and '/System/Library/Java/Extensions
'.<JAVA_HOME>/jre/lib/ext
' (e.g., '/usr/user/java/jdk1.8.0_xx/jre/lib/ext
') and '/usr/java/packages/lib/ext
'.java.ext.dirs
'. You can print its contents via System.out.println(System.getProperty('java.ext.dirs'))
.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 '.
'). CLASSPATH
in Control Panel ⇒ System ⇒ Advanced system settings ⇒ Advanced ⇒ Environment Variables ⇒ System Variables ⇒ New ⇒ In 'Variable name', enter 'CLASSPATH
' ⇒ In 'Variable value', enter '.;path1xxx.jar;path2yyy.jar
', where the entries are separated by a semi-colon (;
).~/.profile
or ~/.bash_profile
(or /etc/profile
for system-wide setting) to include the following line at the end of the file: The entries are separated by colon (:
).CLASSPATH
in the javac
/java
command-line via the option -cp <paths>
(or -classpath <paths>
), for example, 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 (Archive) library), or '.so
' (Unix's Shared Object 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:
c:windowssystem32
(Windows), /usr/lib
or /usr/local/lib
(macOS / Unix). 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'))
.java
's command-line option -Djava.library.path=xxx
, for example, Using an IDE can greatly simplifies inclusion of external packages. Read 'Eclipse How-To' or 'NetBeans How-To'.
Link to References & Resources