String assignment ?

Question

Hi,
in the following code:
public class Test {
public static void main(String[] args) {
String s = new String("Welcome to Java");
Object o = s;
String d = (String)o;
System.out.println(o + s + d);
Both strings and the object are referring to the same string object., and the println shows 3 "Welcome to Java" 's. I don't understand exactly why this is so? I was hoping someone might be able to explain it to me.
Thanks!
Jimbo
think

Answer 1

First of all, I was under the impression that when
you declare a string variable and use the new keyword
that what you were doing was constructing a String
object (to which you can apply the functions of the
String class). Yes. But you don't NEED to do new String(...) to get a String object. Usually you just assign it to a String literal (s = "abc";) or get it from a config file or user input, or call some object's toString() method.
I am unclear what is actually happening when the code
"Object o = " was used. Is the Object class the
super (or parent) class, so that a String is
automatically in the Object class because it is its
parent? Correct.
I take it that after that line of code, we
have two reference variables pointing at the
String......and then the second "String = " statement
is just making another reference to the same String.Correct.
With the family example you gave me.....applying it
this string.....the three variables are just three
different points of reference to the same string. Correct.
As far as why I thought it might be any
different....earlier on in the class
we had code that went kinda like this:
String s = "me";
String t = "you";
s = t;
I guess in this case we lost our reference to the
String "me", so if we println s and t we get two
"you" 's.Correct. So, why would printing a + b + c (or whatever your variables were in the initial post) produce anything but three of the same thing? I still don't know what you expected or why.
I guess I was getting this all
confused....probably making it more difficult than it
actually is...but I have a lot coming at me at
once.....Actually, it sounds like you have a better handle on how Java's reference variables work than most beginners. The idea that the variable holds a reference, not an object, and that assignment doesn't copy an object, comes hard to some people. You sound like you understand that part of it.