What you could do is creating an instance of a GregorianCalendar and then set the Date as a start time:
Date date;
Calendar myCal = new GregorianCalendar();
myCal.setTime(date);
However, another approach is to not use Date at all. You could use an approach like this:
private Calendar startTime;
private long duration;
private long startNanos; //Nano-second precision, could be less precise
...
this.startTime = Calendar.getInstance();
this.duration = 0;
this.startNanos = System.nanoTime();
public void setEndTime() {
this.duration = System.nanoTime() - this.startNanos;
}
public Calendar getStartTime() {
return this.startTime;
}
public long getDuration() {
return this.duration;
}
In this way you can access both the start time and get the duration from start to stop. The precision is up to you of course.