Java system properties and environment variables
System properties are set on the Java command line using the
-Dpropertyname=valuesyntax. They can also be added at runtimeusingSystem.setProperty(String key, String value)or via the variousSystem.getProperties().load()methods.
To get a specific system property you can useSystem.getProperty(String key)orSystem.getProperty(String key, String def).Environment variables are set in the OS, e.g. in Linux
export HOME=/Users/myusernameor on WindowsSET WINDIR=C:\Windowsetc,and, unlike properties, may not be set at runtime.
To get a specific environment variable you can useSystem.getenv(String name).
I think the difference between the two boils down to access. Environment variables are accessible by any process and Java system properties are only accessible by the process they are added to.
Also as Bohemian stated, env variables are set in the OS (however they 'can' be set through Java) and system properties are passed as command line options or set via setProperty().