Mobile

public class Reader extends Activity {
    private String ID;
    public void setID(String id) {
	ID = id;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.activity_reader);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
	getMenuInflater().inflate(R.menu.activity_reader, menu);
	return true;
    }
}

public class MainActivity extends Reader {
	
    @Override
    public void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setID("bla_bla_bla");
    }
}

Eclipse Quote:

The method setID(String) is undefined for the type MainActivity