BufferedReader is = new BufferedReader(new InputStreamReader(System.in));
e fai cosi:

//DataInputStream is;
BufferedReader is;
PrintStream os;

public prova(OutputStream os)
{
this.is = new BufferedReader(new InputStreamReader(System.in));
this.os = new PrintStream(os);
}

Ciao fAbio
Fammi sapere se funziona!!!