passing by reference

[Vidya Krishnamurthi]

class I {
private String name;
public String name() {return name;}
public I(String s) {name = s;}
}
class J {
public static void m1(I i) {i = null;}
public static void main (String[] args) {
I i = new I("X"); // 1
m1(i); // 2
System.out.print(i.name()); // 3
}
}

Which of the following are true statements and which of the following could be a result of attempting to compile and run the program?
a. The object created a line 1 is eligible for garbage collection after line 2.
b. A NullPointerException is generated at line 3.
c. Prints X.
d. Compiler error.
e. None of the above
ans is c
I thought it was passed by reference
when u do
i=i
Can any one please explain
Thanks in advance..

[G Nadeem]

Hi Vidya,
this is how i will interpret it....
a copy of the reference to object I is passed to the method 'm1'. so the local variable 'i' of the method 'm1' points to object I at line 1. now if we do any operation directly on 'i' like i.aMethod(), it will effect I object (I being object and not a primitive). however if the reference i is changed to point to someother object/null (using = operator), the orignal reference i at line 1 will not be effected. since 'i' in method 'm1' is local variable of 'm1'.
[ June 04, 2003: Message edited by: G Nadeem ]

[Brian Joseph]

Key: A "copy of the reference" (not the object of course) is passed. I think of reference variables as holding some type of address value which refers to the object in memory. A copy of that address is passed to the method parameter. The method parameter itself is a unique variable.