The list of standard system properties is documented in System.getProperties(). It includes a few different encoding-related properties, in particular stdout.encoding and stderr.encoding. However, there is the possibility that stdin could be redirected to a different location than stdout or stderr, so there should be a system property for stdin as well.

Initially there won't be any uses of stdin.encoding in the JDK, but applications may want to use it in cases where they need to know what encoding to use for reading character data from stdin, for example, using an InputStreamReader or Scanner.

We also expect that there will be future uses for such a property in the JDK.