EDIT) Using objects as parameters in a method call

Question

public class incrementer {

public incrementer () {

    counter =1;
}

public incrementer (int startValue) {
    counter = startValue;
}

public int nextValue() {
    int temp = counter;
    counter++;
    return (temp);

}


private int counter;
}


import acm.program.*;

public class useCounter extends ConsoleProgram {
public void run() {
    incrementer count1 = new incrementer();
    incrementer count2 = new incrementer(1000);

    println("Five values for count1 :");
    countFiveTimes(count1);

    println("Five values for count2 :");
    countFiveTimes(count2);

    println("Another five values for count1 :");
    countFiveTimes(count1);



}

private void countFiveTimes(incrementer counter) {
    for (int i=0; i<5; i++) {
        println(counter.nextValue());

    }

}

}

I just learned about the concept of passing objects as parameters in a method call. From my understanding, a run of the useCounter class looks like this:

create count1 = incrementer object with counter value 1

call countFiveTimes method with parameter count1

counter = incrementer object with counter value 1 //assign new name to the object to use it inside the countFiveTimes method//

call nextvalue method with the object(counter at this point, previously count1) and println the return value 5 times.

(first run)

temp = 1;

counter = 2;

return temp

println(temp);

prints 1

(second run)

temp = 2;

counter = 3;

returm temp

println(temp)

prints 2

.... and so on and so forth.

I will skip the count2 part because it isn't relevant to my question.

When the run gets to the println("another 5 values for count1 :"); part, I would normally expect the a run of this part of the class to be the exact same as the first part; that is, I would expect the results to be 1 2 3 4 5 because I do not see the code that is assigning a new value to the counter1 object.(I expect it to be in the same state it was in when I created it)

The explanation my instructor gave was that when you pass on an object as a parameter in a method call, you are essentially passing on the object itself, not a copy of the object.

I feel okay with the concept, but the question is: Where is the new state of the object saved?

Is it in the useCounter class? if it is, where in it?

Help would be much appreciated, sorry for any confusions I might have caused in my question.

EDIT: Result of the run Five values for count1 : 1 2 3 4 5 Five values for count2 : 1000 1001 1002 1003 1004 Another five values for count1 : 6 7 8 9 10

EXPECTED result of the run

Five values for count1 : 1 2 3 4 5 Five values for count2 : 1000 1001 1002 1003 1004 Another five values for count1 : 1 2 3 4 5

Question: I am assuming that the state of the object (count1) is saved after the first five values. Where is it saved? How is it saved when there is no code functioning to save it?

above code should return `1 2 3 4 5`. what are you getting ? — roottraveller, Aug 04 '17 at 07:29
You must read about [passing an object as a reference](https://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value). — Lefteris008, Aug 04 '17 at 07:29
https://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value — Usagi Miyamoto, Aug 04 '17 at 07:30
So much input, and still I dont get your question. A) please spend the time to format/indent **all** of your input (esp. your code) *properly*. B) read about [mcve]. Dont get into lengthy explanations. State what happens and what you expect to happen, ideally using simple examples, not *textual description.* — GhostCat, Aug 04 '17 at 07:31
When you create an "int" object, you are saving it in your RAM so, "incrementer" is another object like "int", "string" etc... It seems like it stays in your ram until you release it... If you mean that. — ReadyFreddy, Aug 04 '17 at 07:33

score 0 · Answer 1 · answered Aug 04 '17 at 07:56

You must understand the concept of Reference and Objects in java. References are pointers to an object. So essentially when you say :

 incrementer count1 = new incrementer();

You are doing 2 things. First an object gets created in the heap and secondly a reference named count1 is created which points to the object in the heap.

When you pass on the "count1" in the method you actually pass the object. This means essentially the object in the heap remains in the heap but an another reference "increment counter" is created which also points to the object pointed to by the count1 reference.

So now what all changes you do on to the object using the reference "counter" effects the same object that is pointed to by count1.

So its like 2 people holding on to a single kite in air using their own strings . Whoever pulls it is the same kite that flies high in air.

I assume that you thought that objects were actually "passed" and then changed and then returned and their state copied back to the original object. This is not the case as I have explained.

EDIT) Using objects as parameters in a method call

1 Answers1