In many blogs and documents, people will say, Java is already eliminat pointer, hence what java pass as parameter is value, the thing that pass through method parameter list is named reference
Let us review what reference and point like in C/C++, which is the most standard stem of program

# include<stdio.h>
int main()
    int data=100, example=3;
    int* pointer=&data;
    int& refer=data;
    printf("%d %d %d\n", data,*pointer,refer);
    printf("%d %d %d\n", data,*pointer,refer);
    printf("%d %d %d\n", data,*pointer,refer);
    printf("%d %d %d\n", data,*pointer,refer);
    printf("%d %d %d\n", data,*pointer,refer);
    printf("%d %d %d\n", data,*pointer,refer);

	return 0;

print result:

100 100 100
20 20 20
50 50 50
70 70 70
70 3 70
3 3 3

from this instance, we got to know three things:

  1. variable, pointer and reference have the capability to change the value of variable.
  2. pointer is a kind of method that will affect variable it pointed to, but it can not change value if this pointer is pointing to another variable (sounds like bullshit!).
  3. reference is a kind of alias that also behave like pointer, but what alias mean is the variable and reference are binded together, when reference or variable changed, the other one also varied.

After review pointer and reference behavior in C++, now let us see what that behave in Java

public class Main
   public static void main(String[] args)
        String a = "Rugal";
        System.out.println("outer before "+a);
        System.out.println("outer after "+a);

    public static void change(String original)
        System.out.println("inner before "+original);
        System.out.println("inner after "+original);

What do you think of the system print are?
According to definition of reference, the result should be:

outer before Rugal
inner before Rugal
inner after Bernstein
outer after Bernstein

also, official document said that in java, the thing that passed is called reference, which ambiguously confused many java developer.
pitfally, the actual print is:

outer before Rugal
inner before Rugal
inner after Bernstein
outer after Rugal

the outer after Rugal means inner original ref is not the same thing in outer a.
which is not an alias like referece in C++.
Do you feel puzzled? because they said java is passed by value, and there is no more pointer. what is wrong with you? what is wrong with me?

To keep you clarified, Let me explain this to you

hint one:

there is no one to gurrantee reference in java is what reference like in C/C++

hint two:

Don’t you think this so called reference in java behave just like what pointer do in C/C++

now you got to know that Java reference is what pointer behave in C/C++
Even if official documentation demonstrated there is no more pointer in Java, and the thing pass through method is called reference is a mendacity, or maybe it is just a conception that result from ambiguity, nobody knows

Thus let us make a deal, that Java is pass-by-value, because what passed into parameter list is the actual address value of a object.
But here is a thing, all the so called reference in java is not what reference behave in C++, it is more likely with pointer. nevertheless, this pointer do not have the capability to dereference the address of which it point to.


Java is indeed pass-by-value but the reference is just actually a fundamental functionalitied pointer.


26 December 2013