Calendar variable updates the other when the second is updated?

Question

Hello, I’ve been messing with the Gregoriancalendar class and I’ve come across the following problem:

You had to go from one point in the calendar to the other, then set the first point as the second, then "reset" the second field and go back. basically the following:

GregorianCalendar gc1=new GregorianCalendar();
GregorianCalendar gc2=new GregorianCalendar();
gc1.setTime(meuTempo1);
gc2.setTime(meuTempo2);
while(!gc2.equals(variavel)){//eu tinha que voltar a gc2 até um determinado ponto
//que não necessariamente é igual a gc1.
//percorre o tempo, tirando o tanto de gc2
}
gc1=gc2;//aqui está o problema
gc2.setTime(meuTempo2);

Basically, I walked back through a certain, given a gc1=gc2and I again set gc2 as it was before. The problem is that when I gave the gc2.setTime(meuTempo2); the gc1 variable also received that parameter, i.e., the attributes of gc1 also changed, as if I had placed a second line gc1.setTime(meuTempo2);.

It was easy to fix, just replace gc1=gc2 for gc1.setTime(gc2.getTime()); but I was in doubt, if I instated a new variable, shouldn’t she take the attributes and then be independent of the second one? If not, in which cases can this happen? And if possible, how to treat this problem?

Answer 1

Do gc1=gc2 does not copy the values of the gc2 for gc1. In doing so, you are copying the reference to gc2 for gc1. On a lower level, it means gc1 and gc2 point now to the same memory address where the type object is GregorianCalendar. Therefore, any change in the attribute that is made through the gc1 and of gc2 is affecting the same object.

In the case of GregorianCalendar, you can copy attribute values using the method clone. Something like that:

gc1 = (GregorianCalendar)gc2.clone();

Note that the above code is assigning a new object GregorianCalendar for gc1 with the cloned values of gc2.