Get first/last date of current Week/Month

import java.util.Calendar;
import java.util.Date;

/**
 * Returns the date of previous Monday
 */
public static Date getFirstDateOfCurrentWeek() {
    Calendar cal = Calendar.getInstance();
    cal.set(Calendar.HOUR_OF_DAY, 0);
    cal.clear(Calendar.MINUTE);
    cal.clear(Calendar.SECOND);
    cal.clear(Calendar.MILLISECOND);
    cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
    return cal.getTime();
}

/**
 * Returns the date of next Sunday.
 */
public static Date getLastDateOfCurrentWeek() {
    Calendar cal = Calendar.getInstance();
    cal.set(Calendar.HOUR_OF_DAY, 0);
    cal.clear(Calendar.MINUTE);
    cal.clear(Calendar.SECOND);
    cal.clear(Calendar.MILLISECOND);
    cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);

    Calendar last = (Calendar) cal.clone();
    last.add(Calendar.DAY_OF_YEAR, 7);
    last.add(Calendar.MILLISECOND, -1);
    return last.getTime();
}

/**
 * Get the first Date ( first millisecond ) of current month
 */
public static Date getFirstDateOfCurrentMonth() {
    Calendar cal = Calendar.getInstance();
    cal.set(Calendar.HOUR_OF_DAY, 0);
    cal.clear(Calendar.MINUTE);
    cal.clear(Calendar.SECOND);
    cal.clear(Calendar.MILLISECOND);
    cal.set(Calendar.DAY_OF_MONTH, 1);
    return cal.getTime();
}

/**
 * Get the last time ( last millisecond ) of current month
 */
public static Date getLastDateOfCurrentMonth() {
    Calendar cal = Calendar.getInstance();
    cal.set(Calendar.HOUR_OF_DAY, 0);
    cal.clear(Calendar.MINUTE);
    cal.clear(Calendar.SECOND);
    cal.clear(Calendar.MILLISECOND);
    cal.add(Calendar.MONTH, 1); // NEXT MONTH
    cal.set(Calendar.DAY_OF_MONTH, 1); // FIRST DAY OF NEXT MONTH
    cal.add(Calendar.MILLISECOND, -1); // Go one Millisecond back, which is the last moment of the last day of current month
    return cal.getTime();
}

BlackBerry DateTimePicker: Selecting a date withing 7 days from now

DateTimePicker can be used to select a particular date. After user selects a date, it can be checked whether the date is within a particular period of time using the after() and before() methods of Calendar.

The DateTimePicker is shown each time the DateTimePicker.doModal()  method is called. A Calendar object of the selected date can be found by calling the DateTimePicker.getDateTime() method.

private String dateText;
Calendar todaysDate = Calendar.getInstance();

public void pickDate()
{
 DateTimePicker datePicker = null;
 
 Calendar dateAfter7days = Calendar.getInstance();
 
 long millsAfter7Days = System.currentTimeMillis() + 6*24*60*60*1000 ;
 dateAfter7days.setTime(new Date(millsAfter7Days));
 
 datePicker=DateTimePicker.createInstance(todaysDate,"MMMM dd, yyyy",null);
 if(datePicker.doModal())
 {
  if(
    datePicker.getDateTime().before(todaysDate)
    || 
    datePicker.getDateTime().after(dateAfter7days)   
  ) {
   final String current = 
    todaysDate.get(Calendar.DAY_OF_MONTH) +
    "/" +
    ( todaysDate.get(Calendar.MONTH)+1 ) +
    "/"+
    todaysDate.get(Calendar.YEAR);
   
   final String after7days = 
    dateAfter7days.get(Calendar.DAY_OF_MONTH) +
    "/" +
    ( dateAfter7days.get(Calendar.MONTH)+1 ) +
    "/"+
    dateAfter7days.get(Calendar.YEAR);
   
   UiApplication.getUiApplication().invokeLater(new Runnable() {      
     public void run() {
       Dialog.alert("Date should be within "+ current +" to " + after7days ); 
     }
   });
  } else {
   Calendar chosenDate = datePicker.getDateTime();
   dateText =
    chosenDate.get(Calendar.DAY_OF_MONTH) +
    "/" +
    ( chosenDate.get(Calendar.MONTH)+1 ) +
    "/"+
    chosenDate.get(Calendar.YEAR);
  }
 }
}