首先找出存储环境变量的位置

emacs bash_profile zshrc中

设置环境变量步骤:- .单击“确定”

从JAVA下载jdk 双击安装它 现在在文件中设置环境变量 a. emacs。你可以使用这个链接或看到下面的截图

b.对于ZSH配置文件设置-

1. export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_112.jdk/Contents/Home

2. source ~/.zshrc - Restart zshrc to reflect the changes.

3. echo $JAVA_HOME - make sure path is set up properly 
   ----> /Library/Java/JavaVirtualMachines/jdk1.8.0_112.jdk/Contents/Home

4. java -version 

   -->  java version "1.8.0_112"  Java(TM) SE Runtime Environment (build 1.8.0_112-b16)Java HotSpot(TM) 64-Bit Server VM (build 25.112-b16, mixed mode)

所有设置现在您可以轻松升级或降级JAVA版本..

来自Apple官方java_home(1)手册页:

**USAGE**

   /usr/libexec/java_home  helps  users  set a $JAVA_HOME in their login rc files, or provides a way for
   command-line Java tools to use the most appropriate JVM which can satisfy a minimum version or archi-
   tecture  requirement.  The --exec argument can invoke tools in the selected $JAVA_HOME/bin directory,
   which is useful for starting Java command-line tools from launchd plists without hardcoding the  full
   path to the Java command-line tool.

   Usage for bash-style shells:
          $ export JAVA_HOME=`/usr/libexec/java_home`

   Usage for csh-style shells:
          % setenv JAVA_HOME `/usr/libexec/java_home`

使用jenv，它就像一个Java环境管理器。它非常容易使用和清洁

对于Mac，请按照以下步骤操作:

brew install jenv

git clone https://github.com/gcuisinier/jenv.git ~/.jenv

安装:如果您正在使用bash，请遵循以下步骤:

$ echo 'export PATH="$HOME/.jenv/bin:$PATH"' >> ~/.bash_profile

echo 'eval "$(jenv init -)"' >> ~/.bash_profile

$ exec $SHELL -l

向jenv添加所需的JVM版本:

jenv add /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home

jenv add /System/Library/Java/JavaVirtualMachines/1.8.0.jdk/Contents/Home

检查已安装版本:

jenv versions

设置您想要使用的Java版本:

jenv global oracle64-1.6.0

非常简单的答案:

运行并获取所有已安装的JDK路径

/usr/libexec/java_home -V

从jenv.be直接运行命令

git clone https://github.com/jenv/jenv.git ~/.jenv #Linux/macOS
OR
brew install jenv #macOS

echo 'export PATH="$HOME/.jenv/bin:$PATH"' >> ~/.zshrc
$ echo 'eval "$(jenv init -)"' >> ~/.zshrc

jenv add PATH_FROM_STEP_1

JDK Switch脚本

我改编了上面@Alex的答案，并编写了以下代码来修复Java 9的代码。

$ cat ~/.jdk
#!/bin/bash

#list available jdks
alias jdks="/usr/libexec/java_home -V"
# jdk version switching - e.g. `jdk 6` will switch to version 1.6
function jdk() {
  echo "Switching java version $1";

  requestedVersion=$1
  oldStyleVersion=8
  # Set the version
  if [ $requestedVersion -gt $oldStyleVersion ]; then
    export JAVA_HOME=$(/usr/libexec/java_home -v $1);
  else
    export JAVA_HOME=`/usr/libexec/java_home -v 1.$1`;
  fi

  echo "Setting JAVA_HOME=$JAVA_HOME"

  which java
  java -version;
}

切换到Java 8

$ jdk 8
Switching java version 8
Setting JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home
/usr/bin/java
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)

切换到Java 9

$ jdk 9
Switching java version 9
Setting JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home
/usr/bin/java
java version "9.0.1"
Java(TM) SE Runtime Environment (build 9.0.1+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)

我使用我写的fish函数

function javav
  set min_version 8
  set max_version 99
  set java_home_cmd '/usr/libexec/java_home 2>/dev/null --failfast --version'

  if ! test (eval $java_home_cmd $argv)
    echo "Version not found"
    return 1
  end

  for current_version in (seq $min_version $max_version)
    set path_to_remove (eval $java_home_cmd $current_version)
    if ! test -z $path_to_remove
      echo 'Removing' $path_to_remove 'from PATH'
      set PATH (string match --invert $path_to_remove/bin $PATH)
    end
  end

  echo 'Setting up env for Java' $argv
  set -x JAVA_HOME (eval $java_home_cmd $argv)
  set PATH $JAVA_HOME/bin $PATH
end

它基本上自动化了这个答案中的步骤，类似于这个，但也负责设置PATH。

只要把它放在.config/fish/functions/中，然后像这样使用它:

javav 11 # Sets to Java 11
javav 16 # Sets to Java 16