Java Basics - Assignment Inside Scope

Question

Can someone explain this to me as I'm relatively new to Java and coming from objective-c background (difference being, pass by reference instead of pass (reference) by value).

Given that Java is pass by value I shouldn't expect to be able to re-assign variables within a different scope and have those changes persist, right? Thats why objectValue is null. String and int are primitives so thats why they work. But, why does Integer work?

Object objectValue = null;
int intValue;
String stringValue = null;
Integer integerValue = null;

if (true) {
    objectValue = new Aircraft();
    intValue = 1;
    stringValue = "is one";
    integerValue = new Integer(1);
}

// objectValue == null
// intValue == 1
// stringValue == "is one"
// integerValue == 1

[Java is *pass-reference-by-value*](http://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value?rq=1) — gla3dr, Aug 25 '15 at 15:48
And why do you think `objectValue` will be `null` after the `if` condition? — Codebender, Aug 25 '15 at 15:50
If `objectValue` is coming out null after that you have a borked computer. It should not be null. — Boann, Aug 25 '15 at 15:50
There are no passes here. You're simply assigning variables. — Maroun, Aug 25 '15 at 15:50

score 8 · Accepted Answer · answered Aug 25 '15 at 15:49

8

You are not using pass by reference or by value. The local variable should be altered in each case.

Pass by value only applies to variables passed as arguments to method calls.

Variables are not passed to nested scopes, there is only one variable for these scopes and changing it alters the original.

The only time variables are copied is for anonymous inner classes and lambdas, however these variables need to be effectively final.

answered Aug 25 '15 at 15:49

Peter Lawrey

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@sᴜʀᴇsʜᴀᴛᴛᴀ They are all related and give context IMHO. – Peter Lawrey Aug 25 '15 at 16:00
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**drinks more coffee** – Aug 25 '15 at 16:05
@anders programming is like mental juggling, when a lot if it is new you don't know what is strange and what is not. Like juggling a sword, a club, a frizzby and ticking bomb. ;) – Peter Lawrey Aug 25 '15 at 16:12

score 2 · Answer 2 · edited Aug 25 '15 at 15:54

2

You are not passing anything to any where in your whole code. You are just reassigning that values to the initially declared variables. That's all.

edited Aug 25 '15 at 15:54

Praveen Kumar Purushothaman

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answered Aug 25 '15 at 15:51

Suresh Atta

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score 0 · Answer 3 · answered Aug 25 '15 at 15:52

0

The "pass reference by value" is referring to method (function) calls. You don't call any methods, so the concept is meaningless.

answered Aug 25 '15 at 15:52

Andreas

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score 0 · Answer 4 · answered Aug 25 '15 at 15:52

0

You don't pass by value when reaching a scope block. That would be a nightmare. What would you do with if statements and for loops? Everything would break.

You only pass by value in functions, and then you pass references by value.

answered Aug 25 '15 at 15:52

P45 Imminent

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Java Basics - Assignment Inside Scope

4 Answers4