Java Pass By Value and Pass By Reference.

Java is strictly ‘Pass By Value’

For Java newbies, this explanation on java pass by reference can be confusing. It would be
better to explain by example. The reason is because with Java
primitives, the results are different than with objects.

The problem comes in because, for primitives, the value of the
argument can be altered (in the method), but it doesn’t affect the
source variable. With an object reference being passed, that
object can be operated on (in the method) and its values changed.

Big difference.

very good explanation on pass by value and pass by reference in java. thanks.

If the callee function can change the object’s values passed, then it should be called as pass by reference right?

Hi Moderator/Owner could you please explain a bit more, the answers here sounds confusing.

Thanks

Got the answer here..
CHeck this out.

http://www.javaworld.com/javaworld/javaqa/2000-05/03-qa-0526-pass.html

I WANTS TO KNOW THE OOPS CONCEPTS IN JAVA

Explanation between pass by value and java pass by reference is confusing. can you give a sample java source code?

java does not support pointers, thus anything is always passed by value.

Yes There is pass by reference in java..
Reference are passed by value to the function is nothing but pass by reference…. but the primitives are always passed by value

GOOD

Good Explanation to understand the concept.

CAN U ABLE TO PROVIDE ME AN EXAMPLE THAT GIVES A DIFFERENCE BETWEEN PASS BY VALUE AND PASS BY REFERNCE

Do more clear bcoz it is not more clear.Difference between Pass by value and Pass by Reference.

Please Keep One Example Program….

Why Java Does’nt Support pointers ????

thank you for your explanation

Here is the sample program

public class TestPassByReference {

/**
* @param args
*/
public static void main(String[] args) {
Reference ref = new Reference();

System.out.println(“The reference of ref=” + ref);
System.out.println(“The reference of ref=” + ref.name);

getValue(ref);
System.out.println(“The reference of ref=” + ref.name);
System.out.println(“The reference of ref=” + ref.getName());

}

public static void getValue(Reference r) {
r.setName(“Prashant”);

}

public static class Reference {
public String name;

public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}

public void Reference(String name) {
this.name = name;
}
}
}

what is the pass by reference and pass by value and pass by address

Passing by value: This method copies the value of an argument into the formal parameter of the subroutine.
Passing by reference: In this method, a reference to an argument (not the value of the argument) is passed to the parameter.

An arraylist and other types of collections do not neccesarly contain objects but it contains refrences to Objects, so you can use an ArrayList to pass refrences in Java, example:

public class Book {
String title;
public Book(String title){
this.title = title;
}

public void setTitle(String newTitle) {
this.title = newTitle;
}

public String getTitle() {
return this.title;
}
}

public class Example {

public static void main(String[] args){

Example example = new Example();
ArrayList bookList = new ArrayList();
bookList.add(0, new Book(“First book”));
bookList.add(1, new Book(“Second book”));
bookList.add(2, new Book(“Third book”));

//we pass an object containing refrences :)
example.demonstrate(bookList);

//proof that its not only pass by value
System.out.println(bookList.get(0).getTitle());

}

public void demonstrate(ArrayList aBookList){
aBookList.get(0).setTitle(“Changed the First title by refrence”);
}
}

ljknjn

very precise, and to the point, thanks a lot

i want to become a great java developer,also want to be master in java program.can u suggest some sites to learn java code properly.

Thx you a lot, it’s clear.

As I understand, Java is strictly supports pass by value .

If variable is passed as argument inside a method, copy of the value is passed. So, it will not affect the original value of variable (for primitive types).

But, if object reference is passed, copy of the value of memory address is passed. So, we able to change the value of an object.

Joe, Is my understanding right?

**muthu
u r ryt…and dis was d correct explanation for d new ones…

Hy Iam Hacker

Hello Guyz

its mean pass by reff actually using value of that reff or one copy of reff of object. m i right??

I found this over the net. Quite a nice explanation.

This will give you some insights of how Java really works to the point that in your next discussion about Java passing by reference or passing by value you’ll just smile :-)

Step one please erase from your mind that word that starts with ‘p’ “_ _ _ _ _ _ _”, especially if you come from other programming languages. Java and ‘p’ cannot be written in the same book, forum, or even txt.

Step two remember that when you pass an Object into a method you’re passing the Object reference and not the Object itself.

Student: Master, does this mean that Java is pass-by-reference?
Master: Grasshopper, No.

Now think of what an Object’s reference/variable does/is:

A variable holds the bits that tell the JVM how to get to the referenced Object in memory (Heap).
When passing arguments to a method you ARE NOT passing the reference variable, but a copy of the bits in the reference variable. Something like this: 3bad086a. 3bad086a represents a way to get to the passed object.
So you’re just passing 3bad086a that it’s the value of the reference.
You’re passing the value of the reference and not the reference itself (and not the object).
This value is actually COPIED and given to the method.

In the following (please don’t try to compile/execute this…):

1. Person person;
2. person = new Person(“Tom”);
3. changeName(person);
4.
5. //I didn’t use Person person below as an argument to be nice
6. static void changeName(Person anotherReferenceToTheSamePersonObject) {
7. anotherReferenceToTheSamePersonObject.setName(“Jerry”);
8. }

What happens?

The variable person is created in line #1 and it’s null at the beginning.
A new Person Object is created in line #2, stored in memory, and the variable person is given the reference to the Person object. That is, its address. Let’s say 3bad086a.
The variable person holding the address of the Object is passed to the function in line #3.
In line #4 you can listen to the sound of silence
Check the comment on line #5
A method local variable -anotherReferenceToTheSamePersonObject- is created and then comes the magic in line #6:
The variable/reference person is copied bit-by-bit and passed to anotherReferenceToTheSamePersonObject inside the function.
No new instances of Person are created.
Both “person” and “anotherReferenceToTheSamePersonObject” hold the same value of 3bad086a.
Don’t try this but person==anotherReferenceToTheSamePersonObject would be true.
Both variables have IDENTICAL COPIES of the reference and they both refer to the same Person Object, the SAME Object on the Heap and NOT A COPY.

A picture is worth a thousand words:

Pass by Value

Note that the anotherReferenceToTheSamePersonObject arrows is directed towards the Object and not towards the variable person!

If you didn’t get it then just trust me and remember that it’s better to say that Java is pass by value. Well, pass by reference value. Oh well, even better is pass-by-copy-of-the-variable-value! ;)

Now feel free to hate me but note that given this there is no difference between passing primitive data types and Objects when talking about method arguments.

You always pass a copy of the bits of the value of the reference!

If it’s a primitive data type these bits will contain the value of the primitive data type itself.
If it’s an Object the bits will contain the value of the address that tells the JVM how to get to the Object.

Java is pass-by-value because inside a method you can modify the referenced Object as much as you want but no matter how hard you try you’ll never be able to modify the passed variable that will keep referencing (not p _ _ _ _ _ _ _) the same Object no matter what!

The changeName function above will never be able to modify the actual content (the bit values) of the passed reference. In other word changeName cannot make Person person refer to another Object.

Of course you can cut it short and just say that Java is pass-by-value!

Not at all good explanation. I had to search on other sites / forum to get more detailed understanding.

Please elaborate with examples, like you do in other posts

good explanation of pass by value and pass by reference.

Can U explain pass By value and pass By reference with example? I have in confusion so.

Thanks in advance.

Please give easy example of pass by reference like swapping of a two number using pass by reference

very useful!!!

it was up to mark.
excellent!!!!!!!

Thanks dude for your help in java
But i also don’t understand the concept of”
Stack unwinding exception”in java

finally in java call-by-reference is not possible is it right?

Yes

Explanation is good.. Brief explanation about the topic from venu is also good.

your blog inter face is very nice i like it…

Thanx to Venu for this beautifull explanation.
@Joe: Can you please update your comment section functionality so that we can write reply to the specific comment. :)

Thanks , it’s very useful and nice.

kindly give some simple examples of link list in Java

Explain the statement ‘java is strictly pass by value’ consider the below piece of code:

import java.util.*;

public class A{

public static void main(String args[]){

ArrayList a=new ArrayList();
a.add(“1″);
System.out.println(a);

somemethod(a);
System.out.println(a);

}//main

public static void somemethod(ArrayList a){
a.add(“2″);
}
}//class

The output of this code will be:
[1]
[1, 2]

Since a reference to the arraylist was passed into the method….no?

String s=”my name is nani”
how can pass a string in arraylist