First run /usr/libexec/java_home -V which will output something like the following:

Matching Java Virtual Machines (3):
1.8.0_05, x86_64:   "Java SE 8" /Library/Java/JavaVirtualMachines/jdk1.8.0_05.jdk/Contents/Home
1.6.0_65-b14-462, x86_64:   "Java SE 6" /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
1.6.0_65-b14-462, i386: "Java SE 6" /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home

/Library/Java/JavaVirtualMachines/jdk1.8.0_05.jdk/Contents/Home

Pick the version you want to be the default (1.6.0_65-b14-462 for arguments sake) then:

export JAVA_HOME=`/usr/libexec/java_home -v 1.6.0_65-b14-462`

or you can specify just the major version, like:

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

Now when you run java -version you will see:

java version "1.6.0_65"
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-462-11M4609)
Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-462, mixed mode)

Add the export JAVA_HOME… line to your shell’s init file.

For Bash (as stated by antonyh):

export JAVA_HOME=$(/usr/libexec/java_home -v 1.8)

For Fish (as stated by ormurin)

set -x JAVA_HOME (/usr/libexec/java_home -d64 -v1.8)

Updating the .zshrc file should work:

nano ~/.zshrc

export JAVA_HOME=$(/usr/libexec/java_home -v 1.8.0)

Press CTRL+X to exit the editor Press Y to save your changes

source ~/.zshrc
echo $JAVA_HOME
java -version

In mac it's pretty simple you can have two or many java versions and based on your requirement you can change that.

I found a very useful tool called jenv.

If you have already had homebrew (a package installer in mac), you can skip this step.

1. For installing or updating homebrew

   /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"
   

2. Installing JEnv - java version manager a cool tool helps you to switch between multiple java env on your mac

   brew install jenv
   

3. Adding jEnv to your path depends on the shell you are using ~/.bash_profile or ~/.bashrc , for zsh it's ~/.zshrc. Add these two lines in your bash profile file

   export PATH="$HOME/.jenv/bin:$PATH"
   eval "$(jenv init -)"
   

4. Restart the terminal or use source ~/.zshrc

5. Check if your JEnv is correctly installed

   jenv doctor
   

   you will get the output something like [OK] Jenv is correctly loaded

6. for installing java 8

     brew install --cask AdoptOpenJDK/openjdk/adoptopenjdk8
   

7. for installing java 11

   brew install --cask AdoptOpenJDK/openjdk/adoptopenjdk11
   

8. for list down all the java on your machine

   /usr/libexec/java_home -V
   

9. Now add these paths to jENV

   Syntax: 
   jenv add <your_jdk_path>
   
   Example:
   jenv add /Library/Java/JavaVirtualMachines/openjdk-14.0.1.jdk/Contents/Home
   

10. All done. Check your version

    jenv versions
    

11. For setting system wide java version

     jenv global 14.0
    

12. For setting locally to terminal

     jenv local 11
    

13. if you are using maven or gradle for your project

      # ensure that JAVA_HOME is correct
      jenv enable-plugin 
    
      export# make Maven aware of the Java version in use 
      (and switch when your project does)
      jenv enable-plugin maven
    

A reference guide https://www.jenv.be/