Access to properties and environment variables

public class AccessProperties {
    public static void main(String[] args) {
        // Sets the system property indicated by the specified key.
        System.setProperty("test", "user.test");

        // Gets the system property indicated by the specified key.
        System.out.println(System.getProperty("user.home"));
        System.out.println(System.getProperty("test"));

        // Removes the system property indicated by the specified key.
        System.clearProperty("user.home");

        System.out.println(System.getProperty("user.home"));
    }
}

Output

/Users/myname
user.test
null