Equals of simpledateformat after perform format(..)

Question

Hi,
i need help to understant the behaviour of the jdk in this code segment.
class TestEqual{
public static void main(String[] args)throws ParseException{
SimpleDateFormat simpleDateFormatInstance = new SimpleDateFormat("dd.MM.yyyy HH:mm:ss");
String sDate = "27.04.0099 12:34:56";
SimpleDateFormat clonedSimpleDateFormatInstance = (SimpleDateFormat)simpleDateFormatInstance.clone();
System.out.println(
          simpleDateFormatInstance.equals(clonedSimpleDateFormatInstance)
); //returns True!
Date oDate = simpleDateFormatInstance.parse(sDate);
simpleDateFormatInstance.format(oDate);
System.out.println(
          simpleDateFormatInstance.equals(clonedSimpleDateFormatInstance)
); //returns False!
after perform format(..) the both objects, simpleDateFormatInstance and clonedSimpleDateFormatInstance, are not equal any more.
thanks for help
mr.dje

Answer 1

They may be equivellent, but they are not equal. In other words:
myObject m = new myObject();
myObject n = new myOjbect();
are equivellent at the time of creation, but they are 2 different objects.
When you clone, you get a new object of the same type, seperate and distinct from each other, but having the same data content values.
if you say
myObject m = new myObject():
myOjbect n = m;
then they point to the same object, m == n because they are the same thing, but when you get a clone
myObject m = new myObject();
myOjbect n = m.clone();
then you have to seperate objects.
consider this:
public class myObject{
  BufferedImage myImage = <some image>;
  int i = 0}Now if this had a clone() method what would we want done?
myObject m = new myObject();
myObject n = m.clone();
If they were the same object and we did a m.myImage=null then n.myImage would become null--would we really want that? No, they are sperate and each contains values and subobjects which contain the same values, but retain their distinctness.