Can I pass parameters by reference in Java

Question

I d like semantics similar to C  s ref keyword

User · Answer

I don t think you can  Your best option might be to encapsulate the thing you want to pass  by ref  onto another class instance  and pass the  outer  class s reference  by value   If you see what I mean     i e  your method changes the internal state of the object it is passed  which is then visible to the caller

User · Answer

In Java there is nothing at language level similar to ref  In Java there is only passing by value semantic   For the sake of curiosity you can implement a ref-like semantic in Java simply wrapping your objects in a mutable class   public class Ref lt T gt         private T value       public Ref T value            this value   value             public T get             return value             public void set T anotherValue            value   anotherValue              Override     public String toString             return value toString                Override     public boolean equals Object obj            return value equals obj               Override     public int hashCode             return value hashCode              testcase   public void changeRef Ref lt String gt  ref        ref set  bbb              Ref lt String gt  ref   new Ref lt String gt   aaa    changeRef ref   System out println ref      prints  bbb

User · Answer

Can I pass parameters by reference in   Java    No   Why   Java has only one mode of passing arguments to methods  by value   Note    For primitives this is easy to understand  you get a copy of the value   For all other you get a copy of the reference and this is called also passing by value   It is all in this picture

User · Answer

Java is always pass by value     When you pass a primitive it s a copy of the value  when you pass an object it s a copy of the reference pointer

User · Answer

Another option is to use an array  e g  void method SomeClass   v    v 0           but 1  the array must be initialized before method invoked  2  still one cannot implement e g  swap method in this way    This way is used in JDK  e g  in java util concurrent atomic AtomicMarkableReference get boolean

User · Answer

Java is confusing because everything is passed by value  However for a parameter of reference type  i e  not a parameter of primitive type  it is the reference itself which is passed by value  hence it appears to be pass-by-reference  and people often claim that it is   This is not the case  as shown by the following   Object o    Hello   mutate o  System out println o    private void mutate Object o    o    Goodbye       NOT THE SAME o    Will print Hello to the console  The options if you wanted the above code to print Goodbye are to use an explicit reference as follows   AtomicReference lt Object gt  ref   new AtomicReference lt Object gt   Hello    mutate ref   System out println ref get       Goodbye   private void mutate AtomicReference lt Object gt  ref    ref set  Goodbye

User · Answer

From James Gosling in  The Java Programming Language           There is exactly one parameter passing mode in Java - pass by value - and that keeps things simple

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