Question

I am a little confused with Java “All passings by value” concept.

Consider the following code:

class Test {
    Integer A;
    String B;
    ...

    void SetVar(Object??? var, Object value) {
        // Set A variable to the value (considering that it's possible)
    }
}

can I code the SetVar function in the way that the following code sets A to 2 and B to Hi??

void Init() {
    SetVar(this.A, 2);
    SetVar(this.B, "Hi");
}

Answer 1

To put it in a nutshell, reassigning a value (meaning with = operator) to an existing reference does not change the object pointing by the original reference.

A big misunderstood in Java is that folks think that they are two types of variables:

• Primitives (like int, boolean etc…)
• References (like Integer, Boolean, custom objects etc…)

Java NEVER uses references. The word Reference is misnomer.

Java only uses Pointers instead for manipulating objects.

To better understand the shade: http://javadude.com/articles/passbyvalue.htm

Regarding your case, even though you skipped the Java Naming Conventions (but it’s another subject), you could solve your “issue” by doing:

void SetVar(Integer value) {
        this.A = value;
}

Indeed, if you pass A as a local parameter (as you did), this local parameter will represent a copy of the A reference since Java is only focused on passed-by-value. So changing it does not affect the initial reference.