Variable scope with a method in Java

Question

I thought I understood variable scope until I came across this bit of code:

private static void someMethod(int i, Account a) {
  i++;
  a.deposit(5);
  a = new Account(80);
}

int score = 10;
Account account = new Account(100);
someMethod(score, account);
System.out.println(score); // prints 10
System.out.println(account.balance); // prints 105!!!

EDIT: I understand why a=new Account(80) would not do anything but I'm confused about a.deposit(5) actually working since a is just a copy of the original Account being passed in...

http://javadude.com/articles/passbyvalue.htm – helpermethod Oct 03 '10 at 08:36 — helpermethod, Oct 03 '10 at 08:36

score 6 · Accepted Answer · answered Oct 03 '10 at 02:20

The variable a is a copy of the reference being passed in, so it still has the same value and refers to the same Account object as the account variable (that is, until you reassign a). When you make the deposit, you're still working with a reference to the original object that is still referred to in the outer scope.

score 3 · Answer 2 · edited May 23 '17 at 12:15

3

It might be time for you to read more about pass-by-value in Java.

edited May 23 '17 at 12:15

Community

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answered Oct 03 '10 at 02:10

matt b

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score 0 · Answer 3 · answered Oct 03 '10 at 06:29

Just may be to make it clear, All variables passed by value means that the called method just gets the values of parameters and not a reference (pointer) to these objects, so any modification on these objects in the method body doesn't affect the outer object. Unlike c++ which has the option to pass the object by reference where the method gets the actual object not it's value, so any modification in the method body affects the outer object.Java doesn't have pass by reference.

But Java has passes in object references, which makes any modification on these objects in the method body **affect** the outer object. — whiskeysierra, Oct 03 '10 at 09:37

score -1 · Answer 4 · answered Oct 03 '10 at 02:10

-1

In java, variables are passed by value.

answered Oct 03 '10 at 02:10

fastcodejava

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I think you should remove this, since objects are passed by reference. – stacker Oct 08 '10 at 20:06
@stacker - how can that be? Just the answer before says it is pass by value. – fastcodejava Oct 08 '10 at 20:44

Variable scope with a method in Java

4 Answers4