How to tell if JRE or JDK is installed

Question

I have one computer that I intentionally installed JDK on  I have another computer with JRE  for  among other things  testing  However  when I got a java application working on this computer  and then tried it on another  it complained that JDK was required  How can I check if JDK was somehow installed on my system  Note  the computer in question is a Mac

User · Accepted Answer

You can open up terminal and simply type

java -version // this will check your jre version
javac -version // this will check your java compiler version if you installed

this should show you the version of java installed on the system (assuming that you have set the path of the java in system environment).

And if you haven't, add it via

export JAVA_HOME=/path/to/java/jdk1.x

and if you unsure if you have java at all on your system just use find in terminal

i.e. find / -name "java"

User · Answer

Normally a jdk installation has javac in the environment path variables     so if you check for javac in the path  that s pretty much a good indicator that you have a jdk installed

User · Answer

A generic  pure Java solution     For Windows and MacOS  the following can be inferred  most of the time       public static boolean isJDK         String path   System getProperty  sun boot library path        if path    null  amp  amp  path contains  jdk              return true            return false      However    on Linux this isn t as reliable    For example      Many JREs on Linux contain openjdk the path There s no guarantee that the JRE doesn t also contain a JDK    So a more fail-safe approach is to check for the existence of the javac executable   public static boolean isJDK         String path   System getProperty  sun boot library path        if path    null            String javacPath               if path endsWith File separator    bin                  javacPath   path            else               int libIndex   path lastIndexOf File separator    lib                if libIndex  gt  0                    javacPath   path substring 0  libIndex    File separator    bin                                   if  javacPath isEmpty                  return new File javacPath   javac   exists      new File javacPath   javac exe   exists                        return false      Warning  This will still fail for JRE   JDK combos which report the JRE s sun boot library path identically between the JRE and the JDK   For example  Fedora s JDK will fail  or pass depending on how you look at it  when the above code is run   See unit tests below for more info      Unit tests     Unix java -XshowSettings properties -version 2 gt  amp 1 grep  sun boot library path    Windows java -XshowSettings properties -version 2 gt  amp 1 find  sun boot library path          PASS  MacOS AdoptOpenJDK JDK11      Library Java JavaVirtualMachines adoptopenjdk-11 jdk Contents Home lib        PASS  Windows Oracle JDK12     c  Program Files Java jdk-12 0 2 bin        PASS  Windows Oracle JRE8     C  Program Files Java jre1 8 0 181 bin        PASS  Windows Oracle JDK8     C  Program Files Java jdk1 8 0 181 bin        PASS  Ubuntu AdoptOpenJDK JDK11      usr lib jvm adoptopenjdk-11-hotspot-amd64 lib        PASS  Ubuntu Oracle JDK11      usr lib jvm java-11-oracle lib        PASS  Fedora OpenJDK JDK8      usr lib jvm java-1 8 0-openjdk-1 8 0 141-1 b16 fc24 x86 64 jre lib amd64           FAIL  Fedora OpenJDK JDK8      usr java jdk1 8 0 231-amd64 jre lib amd64

User · Answer

the computer in question is a Mac    A macOS-only solution    usr libexec java home -v 1 8  --exec javac -version   Where 1 8  is Java 1 8 or higher   Unfortunately  the java home helper does not set the proper return code  so checking for failure requires parsing the output  e g  2 gt  amp 1  grep -v  Unable   which varies based on locale   Note  Java may also exist in  Library Internet Plug-Ins JavaAppletPlugin plugin Contents Home bin  but at time of writing this  I m unaware of a JRE that installs there which contains javac as well

User · Answer

according to JAVA documentation  the JDK should be installed in this path     Library Java JavaVirtualMachines jdkmajor minor macro  update  jdk   See the uninstall JDK part at https   docs oracle com javase 8 docs technotes guides install mac jdk html  So if you can find such folder then the JDK is installed

User · Answer

maciej-cygan described the process well  however in order to find your java path     which java  it gives you the path of java binary file which is a linked file in  usr bin directory  next     cd  usr bin   amp  amp  ls -la   grep java  find the pointed location which is something as follows  for me     then cd to the pointed directory to find the real home directory for Java  next     ls -la   grep java  which is as follows in this case     so as it s obvious in the screenshot  my Java home directory is  usr lib jvm java-11-openjdk-amd64  So accordingly I need to add JAVA HOME to my bash profile   bashrc   bash profile  etc  depending on your OS  like below   JAVA HOME   usr lib jvm java-11-openjdk-amd64   Here you go

[java] How to tell if JRE or JDK is installed

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