This question already has answers here:
Why doesn't java support pass by reference like C++
(2 answers)
Is Java "pass-by-reference" or "pass-by-value"?
(93 answers)
Closed 9 years ago.
Java is strictly pass by value..I am still confused with this concept.
I have gone through many websites to get an answer for this but I am not able to find any good reason.
Is there any proper reason why Java is not pass by reference?
The value of a reference variable is an "address" in Java. When you pass a reference variable to a method, a new reference variable is placed on the stack and a copy of the passed reference variable's value is used to initialize the new local reference varaible's value, just like any primitive type.
That is the classic definition of pass by value.
NOTE: While you can think of the reference as a memory address, it's not. The underlying mechanism makes it act logically as if it were though.
SHORT VERSION: references are simple variables just like the other primitive types for purposes of passing arguments to methods. What you can do with them once passed is obviously different.
Related
This question already has answers here:
Is Java "pass-by-reference" or "pass-by-value"?
(93 answers)
Closed 5 years ago.
In Java sometimes method parameters act like passed by reference, even though they are not.
what method are they passed by?
I know java is always passed by value. But is it possible that it could act like pass by reference
All parameters are passed by value.
Visit https://docs.oracle.com/javase/tutorial/java/javaOO/arguments.html
This question already has answers here:
Is Java "pass-by-reference" or "pass-by-value"?
(93 answers)
How do I pass a variable by reference?
(39 answers)
Python and Java parameter passing [duplicate]
(1 answer)
Closed 5 years ago.
I come from Java and C++, and now I'm learning Python with this tutorial.
To the best of my knowledge, in Java arguments are passed by value. It seems that they are passed by reference, because when the argument is an object, we pass the reference of the object. So, if inside the called function we change the object state, the object will result modified even after the function call. But, if inside the function we reassign the function parameter we are changing the referenced object, which means that from that point the function's argument will not be affected anymore.
A simple example:
void foo(List<Integer> l){
l.append(1); //affecting list_argument
l = new ArrayList<int>();
l.append(2); //not affecting list_argument
}
public static void main(String[] args){
List<Integer> list_argument = new ArrayList<Integer>();
foo(list_argument); //passing list_argument's reference by value
//list_argument contains 1 only
}
Now, I'm reading this article about passing arguments in Python. In the article, it refers to a fancy name strategy called "passing by object", but to me it seems exactly the mechanism that I described above.
So, my question is: is there any difference the passing argument strategy between Python and Java?
This question already has answers here:
Is Java "pass-by-reference" or "pass-by-value"?
(93 answers)
Closed 6 years ago.
I am learning java and in my learning material I found the following question:
You are creating an application that includes a number of methods. These methods will change the values of both primitive and reference variables passed in as arguments. Which statement best describes the effect that changes made in the method will have on the original variables? Choose the best option(s) from those listed below.
The question is whether the value reference type can be changed, and the answer is no. But could anyone help with showing a code which demonstrates this behavior?
Thank you
reference type cant be changed.
Java is a pass by value language.
This means when you invoke a method ,such as
Person p = new Person();
foo(p);
You are pass a copy of reference p.
So you cant change reference type,but you could change the value indicated by the reference.
This question already has answers here:
Is Java "pass-by-reference" or "pass-by-value"?
(93 answers)
How to return multiple objects from a Java method?
(25 answers)
Closed 9 years ago.
I'm a new comer form C#, and I know clearly that "Java is always pass-by-value."
But pass-by-reference is useful when we want to get multiple outputs from one method.
How can we get multiple outputs from one method in java, as in C#.
I know one way to do this -- use a generic wrapper class, and get value from the field.
class Wrapper<T> {
public Wrapper(T value) {
Value = value;
}
public T Value;
}
Is there another way to realize this effect?
No, Java does not have out parameters. You can pass an object reference that the method is to modify to pretend that it has out parameters, but this isn't usually the best design and runs into other issues (multithreading and mutable state for one).
The best way to achieve a method that returns multiple values is to have the method return a type that contains multiple values.
Another way to simulate call by reference in Java is to pass a one-element array as a parameter.
This question already has answers here:
Why doesn't java support pass by reference like C++
(2 answers)
Closed 9 years ago.
Why does java doesn't support pass by reference?
Is there any specific reason for that?*
Why does java doesn't support pass by reference?
Java is indeed pass-by-value. However, you can still pass an object reference into a method. Even though the reference is passed by value, the overall effect is almost indistinguishable from pass-by-reference.
What is not supported is references to primitive types.
Is there any specific reason for that?
That is the language design.
It supports pass by reference in a different sense that the reference is passed by value.
See this: http://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#jls-8.4.1
Actually in Java everything is passed by value.
When you say Objects are passed by reference, that means Object reference is passed by value.
This is basically a design decision taken by Java designers, to make the language simple and the code easier to debug.