added some concise intro with the main steps for installing java

howto/get-java.md

@@ -5,6 +5,15 @@
 To be able to develop in Java one requires a JDK - Java Development Kit. You have to download and properly set up java
 For IT1901 either JDK 11 or 12 will do just fine.
 
+Installing manually the jdk has the following steps no matter what operating system you are using:
+
+* download the archive containing the desired release
+* extract it
+* move it to a meaningful location (depends on the os what is a good location)
+* set up environment variables for `JAVA_HOME` and `PATH`
+* apply changes if necessary
+
+Note: The examples shown here use filenames as they were for jdk 12.0.2 at the moment of redacting the document. Adjust the filenames and the paths as needed. Depending on your OS version or flavour you might have different text editors and you might need to adjust for that as well.  
 
 ## Install java
 
@@ -208,7 +217,7 @@ nano ~/.bash_profile
 
 we add the following line
 
-`export JAVA_HOME="/Library/Java/JavaVirtualMachines/jdk-12.0.2/Contents/Home"`
+`export JAVA_HOME="/Library/Java/JavaVirtualMachines/jdk-12.0.2.jdk/Contents/Home"`
 
 ![](images/mac_08_env03.png)