java's argument is passed by value or by reference

ousys · June 4th, 2006, 04:33 AM

i am puzzled , somebody said java only exits one passing argument rules, that is passed by value , what does that mean?

public void fn1(String a){
  a="aaaa"
}
public static void main(String []args){
  String b="bbb";
  fun1(b);
  System.out.println(b);
}
in the screen , it will show "bbb" ,why?
if passed by reference ,i think it is modified , so it should print out "aaaa"

by the way, is there a way we can get the integer value in the method whose return type is boolean?

Thank you.

mj_kalher · June 10th, 2006, 01:18 AM

I think this code will not work

first changed function name that is fn1() and fun1()
well it may be mistake.

second if u will call this function in main() u must make
it static as main() is static and can call only static methods.

u r prblems solution ....
In java objects are passed as, by reference so
make a class with construcure and declare object in main() of
that class and then pass object as parameter in delared class .

ajit · June 26th, 2006, 09:16 AM

Code:

class PassByValEx
{
    int i;
}
class Test
{
    static void fn(PassByValEx obj)
    {
        obj.i = 10;
    }

    public static void main(String a[])
    {
        int b = 20;
        fn(b);
        System.out.println(b);
    }
}

The above code will display 10. Datatypes like String, int, char are passsed by value. The class we create are passed by reference.

Ajit

arp · June 28th, 2006, 06:18 AM

In Java primitive datatypes(byte, char, int etc..) are Passed By Value whereas objects are Passed By Reference.

Regards,
arp

panacea · July 1st, 2006, 08:33 PM

Arp: Wrong. All parameters are passed by value. It's just that Objects (non-primitives) are passed as pointers, but the pointer is passed as a value. No function can change the value that's passed. That's why in the String example originally proposed, the output is still 'bbb'. The pointer that is "String b" still points to 'bbb' in memory, as is consistent with passing by value. If pass by reference WAS possible (as in Pascal, and with C by using the & character), then the String example would output 'aaaa'.

Jon Emerson
http://www.jonemerson.net/