How do I set the default Java (JDK) version on Mac OS X?

By Wayan in OS X, Tools 13 Comments

In this post you will learn how to set the default JAVA_HOME in Mac OS X when you have more than one JDK installed in your computer. First you need to run /usr/libexec/java_home -V command to get the list of installed JDK. The command will print out something like the following depending on the available JDK in your computer.

On my machine I have the following version of Java.

Matching Java Virtual Machines (3):
    9, x86_64:  "Java SE 9"     /Library/Java/JavaVirtualMachines/jdk-9.jdk/Contents/Home
    1.8.0_121, x86_64:  "Java SE 8"     /Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home
    1.7.0_80, x86_64:   "Java SE 7"     /Library/Java/JavaVirtualMachines/jdk1.7.0_80.jdk/Contents/Home

From the list above pick which version you want to be the default JDK. For example, I will choose the 1.8.0_121 version to be my default JDK. To set it run the command below.

export JAVA_HOME=`/usr/libexec/java_home -v 1.8.0_121`

If the major version of the available JDK is unique you can just use the major version, like:

export JAVA_HOME=`/usr/libexec/java_home -v 1.8`

After setting the JAVA_HOME and you run the java -version command you will see that JDK 1.8 is the new default JDK in your computer.

java version "1.8.0_121"
Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)

The change above will only be active in the current running shell. If you close or terminate the shell, next time you open the shell you will need to set it again. To make this change permanent you need to set it in your shell init file. For example if you are using bash then you can set the command in the .bash_profile. Add the following lines at the end of the file.

# Setting default JDK to version 1.8.
export JAVA_HOME=`/usr/libexec/java_home -v 1.8`

To activate this configuration right away your can run source .bash_profile. This command reads and executes the .bash_profile in the current shell.

How do I set up JAVA_HOME and Path variables in Windows?

By Wayan in Basic, Core API 1 Comment

Setting up a JAVA_HOME and Path variables is the second thing you’ll need to do after installing a JDK (Java Development Kit). Although this is not required by Java itself, it is commonly use by other application. For instance then Apache Tomcat web application server and other application server will need it. Or we might need it if we want to compile or running our Java classes from the command prompt. It helps us to organize the default JDK and the execution path.

So here are the steps that we’ll need to do to configure the JAVA_HOME and Path variable on a Windows operating system.

Step 1. Finding the location of our JDK installation directory. If we already know where we have installed the JDK continue to the Step 2.

  1. The JDK usually installed in the C:\Program Files\Java directory by default.
  2. Under this directory we can find one or more versions of installed JDK, for examples I have jdk-14 and jdk-17. Just choose the default one we’re going to use.

Step 2. Setting JAVA_HOME variable

After we know the location of your JDK installation, we can copy the directory location from the Windows Explorer address bar.

  1. Open Windows Explorer
  2. Right-Click the Computer and select the Properties menu.
  3. Click Advanced system settings and the System Properties windows will be shown.
  4. Select the Advance tab.
  5. Click the Environment Variables button.
  6. A new Environment Variables window will be shown.
  7. Under the System Variables, click the New button to create a new environment variable.
  8. Enter the variable name as JAVA_HOME, all letters are in uppercase.
  9. In the variable value enter the JDK installation path you’ve copy above.
  10. Click OK.

Step 3. Setting the Path variable

After we’ve set the JAVA_HOME variable, now we can update the Path variable.

  1. In the Environment Variables window, under the System Variables section find a variable named Path.
  2. If we don’t have the Path variable we need to add one using the New button.
  3. If we already have the Path variable we’ll need to update its value, click Edit button to update.
  4. Add %JAVA_HOME%\bin; to the beginning of the Path variable value.
  5. Press OK to when we are done.
  6. Press another OK to close the Environment Variables window.

Step 4. Check to see if the settings work

  1. Open your Windows Command Prompt.
  2. Type java -version in the command line.
  3. If everything was set correctly we’ll see the running version of your installed Java JDK.

As an example on my Windows Command Prompt I have something like:

D:\>java -version
java version "17" 2021-09-14 LTS
Java(TM) SE Runtime Environment (build 17+35-LTS-2724)
Java HotSpot(TM) 64-Bit Server VM (build 17+35-LTS-2724, mixed mode, sharing)

If you don’t see the correct output, for instance you get an error like “‘java’ is not recognized as an internal or external command, operable program or batch file.”, please retry the steps described above. Enjoy your new adventure with Java programming. Happy coding!

How do I get Java Home directory?

By Wayan in Core API, Lang Package 0 Comment

To get Java Home directory we can obtain it from system properties using the java.home key.

package org.kodejava.lang;

public class JavaHomeDirectory {
    public static void main(String[] args) {
        String javaHome = System.getProperty("java.home");
        System.out.println("JAVA HOME = " + javaHome);
    }
}

On my computer this code give me the following output:

JAVA HOME = C:\Program Files\Java\jdk-17