When does System.getProperty("java.io.tmpdir") return "c:\temp"

In MS Windows the temporary directory is set by the environment variable TEMP. In XP, the temporary directory was set per-user as Local Settings\Temp.

If you change your TEMP environment variable to C:\temp, then you get the same when you run :

System.out.println(System.getProperty("java.io.tmpdir"));

If you set

-Djava.io.tmpdir=C:\temp

On the one hand, when you call System.getProperty("java.io.tmpdir") instruction, Java calls the Win32 API's function GetTempPath. According to the MSDN :

The GetTempPath function checks for the existence of environment variables in the following order and uses the first path found:

1. The path specified by the TMP environment variable.
2. The path specified by the TEMP environment variable.
3. The path specified by the USERPROFILE environment variable.
4. The Windows directory.

On the other hand, please check the historical reasons on why TMP and TEMP coexist. It's really worth reading.