Gets the system property indicated by the specified key.

First, if there is a security manager, its checkPropertyAccess method is called with the key as its argument. This may result in a SecurityException.

If there is no current set of system properties, a set of system properties is first created and initialized in the same manner as for the getProperties method.

Parameters:

key the name of the system property.

Returns: the string value of the system property, or null if there is no property with that key.

Exceptions:

SecurityException     if a security manager exists and its checkPropertyAccess method doesn't allow access to the specified system property.

NullPointerException     if key is null.

IllegalArgumentException     if key is empty.

`SecurityException`		if a security manager exists and its `checkPropertyAccess` method doesn't allow access to the specified system property.
`NullPointerException`		if `key` is `null`.
`IllegalArgumentException`		if `key` is empty.