Timestamp to string date

I don't know how to transform timestamp to date. I have:

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    TextView czas = (TextView)findViewById(R.id.textView1);
    String S = "1350574775";
    czas.setText(getDate(S));        
}



private String getDate(String timeStampStr){
   try{
       DateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
       Date netDate = (new Date(Long.parseLong(timeStampStr)));
       return sdf.format(netDate);
   } catch (Exception ignored) {
    return "xx";
   }
} 

And answer is: 01/16/1970, but it is wrong.