Java Community | Help. Code. Learn.•4mo ago

Does Java have pass by reference?

Just curious how this works in Java, seems like it isn’t like classic pass by reference in other languages like C/C++.

11 Replies

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dan1st•4mo ago

Java is generally pass-by-value but it may pass references by value With primitive data types, you have normal pass by value but with objects, (which are located in the heap), you always have references to these objects so you are passing these references - but if you reassign them, you have a different object and this is not propagated For example

public class SomeClass {
    private String text;
    public static void caller(){
        SomeClass obj = new SomeClass();
        obj.text = "caller value";
        callee(obj);// you pass the value of the reference to the object
        System.out.println(obj.text);//callee value 1
    }
    private static void callee(SomeClass obj){
        obj.text = "callee value 1";// you update the content of the object - this is the same object the caller uses
        obj = new SomeClass();//you assign obj to another object - now the variable points to an object that isn't the same as the one used by the caller
        obj.text = "callee value 2";// you are changing the content of the different object
    }
}

public class SomeClass {
    private String text;
    public static void caller(){
        SomeClass obj = new SomeClass();
        obj.text = "caller value";
        callee(obj);// you pass the value of the reference to the object
        System.out.println(obj.text);//callee value 1
    }
    private static void callee(SomeClass obj){
        obj.text = "callee value 1";// you update the content of the object - this is the same object the caller uses
        obj = new SomeClass();//you assign obj to another object - now the variable points to an object that isn't the same as the one used by the caller
        obj.text = "callee value 2";// you are changing the content of the different object
    }
}

DaMangoOP•4mo ago

when would you want to pass the references?

dan1st•4mo ago

DaMangoOP•4mo ago

when is it advantageous to pass the object reference err if you're passing the reference of the object by value you don't really get a performance benefit from doing so?

dan1st•4mo ago

What do you mean with that? Using references allows you to have complex/arbitrary object graphs and other structures

DaMangoOP•4mo ago

in c/c++ you might pass by reference to avoid the overhead of copying a variable and using it to reassign the value of the original reference

dan1st•4mo ago

So? You are still passing references by value so the only thing that's copied is the reference

DaMangoOP•4mo ago

what situations have you passed the object reference in java? i'm looking to learn when it might be a good idea to do it vs. when not to

dan1st•4mo ago

Java always passes object references by value in that way which allows you to pass objects and modify them elsewhere it also has some disadvantages like it introducing indirections (following the reference can be a performance cost in a few ways)

JavaBot•4mo ago

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Does Java have pass by reference?

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