输入日期获取当前的星期

下面的代码可以通过当前的时间获取当前的星期，怎么改为输入日期26/8/2013这种格式得到星期的？

Calendar calender = Calendar.getInstance();
Log.d("Current Week:", "" + calender.get(Calendar.WEEK_OF_YEAR));
Toast.makeText(this, "current year weeks is"+ calender.get(Calendar.WEEK_OF_YEAR),   
Toast.LENGTH_SHORT).show();

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import android.net.ParseException;
import android.widget.Toast;

...

Date date;
String dtStart = "26/8/2013"; // Input date from user
SimpleDateFormat format = new SimpleDateFormat("dd/M/yyyy");  
try {  
    date = format.parse(dtStart);
} catch (ParseException e) {  
    // TODO Auto-generated catch block  
    e.printStackTrace();  
}

Calendar calender = new GregorianCalendar();
calender.setTime(date);
Toast.makeText(this, "current year weeks is" + calender.get(Calendar.WEEK_OF_YEAR), Toast.LENGTH_SHORT).show();