Java pass by reference

Question

Why in this code i can't swap StringBuffer's?

 public static void main(String[] args) {
     StringBuffer a = new StringBuffer("One");
     StringBuffer b = new StringBuffer("Two");
     swap(a, b);
     System.out.println("a is " + a + "\nb is " + b);
 }

static void swap(StringBuffer a, StringBuffer b) {
    a.append(" more");
    b = a;
}

You could, of course, make your `swap` method "work", by having it swap *the contents* of the two objects. — Hot Licks, Jul 24 '14 at 20:11
@Ordous - I apologize. He clearly understands how Java works, has thoroughly researched whether Java is call by reference or call by value, and is just jerking our chains. — Hot Licks, Jul 24 '14 at 20:12
Have a look at this answer: http://stackoverflow.com/a/40523/3579095 — Lars, Jul 24 '14 at 20:15
@HotLicks The question is clearly low quality and been discussed multiple times over. I imagine it will be closed or marked as duplicate within seconds. The user will also get his share of downvotes for both asking a silly no-effort question and the *way* he asked it. It's right to show him that (and possibly remove the ability to ask questions if this persists). But being offensive does not help at all. — Ordous, Jul 24 '14 at 20:16

score 0 · Answer 1 · answered Jul 24 '14 at 20:09

0

Because you are not working with the reference of the variables a and b but with new StringBuffer("One") and new StringBuffer("Two") references.

So with b = a you don't change a and b in main but local copies.

answered Jul 24 '14 at 20:09

Marco Acierno

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score 0 · Answer 2 · answered Jul 24 '14 at 20:09

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Java doesn't support pass by reference, only pass by value. StringBuffer a is a reference, and this reference is passed by value.

Please don't use StringBuffer as it was replaced by StringBuilder ten years ago.

answered Jul 24 '14 at 20:09

Peter Lawrey

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score 0 · Answer 3 · answered Jul 24 '14 at 20:10

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static void swap(StringBuffer a, StringBuffer b) {
       a.append(" more");
       b = a; // the change is local to swap(). It doesn't affect main()
}

answered Jul 24 '14 at 20:10

Shlublu

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Java pass by reference

3 Answers3