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System properties are set on the Java command line using the
-Dpropertyname=value
syntax. They can also be added at runtime
usingSystem.setProperty(String key, String value)
or via the various
System.getProperties().load()
methods.
To get a specific system property you can useSystem.getProperty(String key)
orSystem.getProperty(String key, String def)
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Environment variables are set in the OS, e.g. in Linux
export HOME=/Users/myusername
or on WindowsSET WINDIR=C:\Windows
etc,
and, unlike properties, may not be set at runtime.
To get a specific environment variable you can useSystem.getenv(String name)
.