How to set or change the default Java (JDK) version on OS X?

Question

How can you change the default version of Java on a mac?

Answer 1

Here is how I do it on my Linux (Ubuntu / Mint mate), I guess Mac can do it similarly.

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Install & config

Steps:

• [Basic - part]
• Download jdk (the .tgz file) by hand.
• Uncompress & rename properly, at a proper location.
  e.g /mnt/star/program/java/jdk-1.8
• Make a soft link, which will be changed to switch java version later.
  e.g ln -s /mnt/star/program/java/jdk-1.8 /mnt/star/program/java/java
  Thus /mnt/star/program/java/java is the soft link.
• Set JAVA_HOME in a start script.
  Could use file like /etc/profile.d/eric.sh, or just use ~/.bashrc.
  e.g JAVA_HOME=/mnt/star/program/java/java
• Then open a new bash shell. java -version should print the java version.
• [More version - part]
• Download & install more Java version, as need, similar as above steps.
  e.g
  /mnt/star/program/java/jdk-11
• [Switch - part]
• In ~/.bashrc, define variable for various Java version.
  e.g
  _E_JAVA_HOME_11='/mnt/star/program/java/jdk-11'
_E_JAVA_HOME_8='/mnt/star/program/java/jdk-8'
# dir of default version,
_E_JAVA_HOME_D=$_E_JAVA_HOME_8
• In ~/.bashrc, define command to switch Java version.
  e.g
  ## switch java version,
alias jv11="rm $JAVA_HOME; ln -s $_E_JAVA_HOME_11 $JAVA_HOME"
alias jv8="rm $JAVA_HOME; ln -s $_E_JAVA_HOME_8 $JAVA_HOME"
# default java version,
alias jvd="rm $JAVA_HOME; ln -s $_E_JAVA_HOME_D $JAVA_HOME"
alias jv="java -version"
• In terminal, source ~/.bashrc to make the changes take effect.
• Then could switch using the defined commands.

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Commands - from above config

Commands:

• jv11
  Switch to Java 11
• jv8
  Switch to Java 8
• jvd
  Switch to default Java version, which is denoted by _E_JAVA_HOME_D defined above.
• jv
  Show java version.

Example output:

eric@eric-pc:~$ jv
java version "1.8.0_191"
Java(TM) SE Runtime Environment (build 1.8.0_191-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode)

eric@eric-pc:~$ jv11
eric@eric-pc:~$ jv
java version "11.0.1" 2018-10-16 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.1+13-LTS)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.1+13-LTS, mixed mode)

eric@eric-pc:~$ jvd
eric@eric-pc:~$ jv
java version "1.8.0_191"
Java(TM) SE Runtime Environment (build 1.8.0_191-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode)

eric@eric-pc:~$ 

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Mechanism

• It switch by changing the soft link, which is used as JAVA_HOME.

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Tips

• On my machine when install jdk by hand, I keep the minor version, then make a soft link with the major version but without the minor version.
  e.g
  // this is the actual dir,
  jdk1.8.0_191

  // this is a soft link to jdk1.8.0_191
jdk-8

  // this is a soft link to jdk-8 or jdk-11
java

• I define command alias in ~/.bashrc, but define variable in a separate file.
  I am using ~/.eric_var to define the variables, and ~/.bashrc will source it (e.g source $HOME/.eric_var).