Everything in Java is passed by value, is it not? :)

A very good question!

This is always confusing to beginners. Java is passed by value. But the interesting question is, what is the value of the variable?

• If the variable is a primitive data type (int, long, char, boolean, etc.) the variable contains the actual numeric value of the data you stored inside it.
• If the variable has an object as a data type, the value of the variable is a reference to the location of the object.

So let's say you have:

int number = 2;

public int sum(int i) {
     return i + 1;
}

square(number);

number will still be 2. Your result will be stored in a new variable but it doesn't affect number.

Now with an object (let's say an array :-))

String[] colors = {"red", "blue", "green"};

public void replaceFirst(String[] array) {
    array[0] = "yellow";
}

replaceFirst(colors);

In this case the colors array will now be {"yellow", "blue", "green"} Here, the "colors" value is a reference to an array object. That reference is like an address of the array object inside the memory. This reference is copied when the variable is passed to the method, and so the "array" variable inside the method points to the same object as "colors". It doesn't make a copy of the array, it makes a copy of the address to the array. So you can make changes to that original array from within the method.

But it's still not equivalent to "pass by reference". What you can't do is change the "colors" variable itself by making it point to some other object. For example this:

String[] colors = {"red", "blue", "green"};

public void setToNewArray(String[] array) {
    array= new String[3];
}

setToNewArray(colors);

This will not set the "colors" variable to a new array! Because that would mean changing the value of the variable "colors", and making it point to a new object located elsewhere in the memory. The method can't change the "colors" variable itself.

I hope my explanations weren't too confusing!