Java is by-value, by-reference or by-sharing? Illustrated with C++ (ENGLISH)

gistfile1.cpp

#include <iostream>

class MyObject {
	public:
		int x;
};


void object_by_value_modify_member(MyObject o) {
	o.x = 20;
}

void object_by_reference_modify_member(MyObject &o) {
	o.x = 20;
}

void pointer_to_object_modify_member(MyObject *o) {
	o->x = 20;
}

void object_by_value_assign(MyObject o) {
	MyObject newMyObject;
	newMyObject.x = 30; 
	o = newMyObject;
}

void object_by_reference_assign(MyObject &o) {
	MyObject newMyObject;
	newMyObject.x = 30;
	o = newMyObject;
}

void pointer_to_object_assign(MyObject *o) {
	MyObject *newMyObject = new MyObject;
	newMyObject->x = 30;
	o = newMyObject;
	//Memory leak, we don't delete the old object, Java would take care using GC
}

using namespace std;

int main() {
	MyObject object_by_value, object_by_reference; //Q1: Where does the variable live? Where does the instance live?
	MyObject *pointer_to_object = new MyObject; //Q2: Where does the variable live? Where does the instance live?
	object_by_value.x = 10;
	object_by_reference.x = 10;
	pointer_to_object->x = 10;

	//Q3: Which of the 3 strategies is ussed by Java?

	cout <<"ORIGINALS:"<<endl;
	cout <<"BY VALUE: "<<object_by_value.x<<" BY REFERENCE: "<<object_by_reference.x<<" POINTER: "<<pointer_to_object->x<<endl;


	object_by_value_modify_member(object_by_value);
	object_by_reference_modify_member(object_by_reference);
	pointer_to_object_modify_member(pointer_to_object);
	
	cout<<"MODIFY MEMBER"<<endl;
	cout <<"BY VALUE: "<<object_by_value.x<<" BY REFERENCE: "<<object_by_reference.x<<" POINTER: "<<pointer_to_object->x<<endl;

	object_by_value_assign(object_by_value);
	object_by_reference_assign(object_by_reference);
	pointer_to_object_assign(pointer_to_object);
	
	cout <<"ASSIGN"<<endl;
	cout <<"BY VALUE: "<<object_by_value.x<<" BY REFERENCE: "<<object_by_reference.x<<" POINTER: "<<pointer_to_object->x<<endl;

	delete pointer_to_object;
return 0;
}


//FOR THE LAZY
//ORIGINALS:
//BY VALUE: 10 BY REFERENCE: 10 POINTER: 10
//MODIFY MEMBER
//BY VALUE: 10 BY REFERENCE: 20 POINTER: 20
//ASSIGN
//BY VALUE: 10 BY REFERENCE: 30 POINTER: 20

//A1: Both live on the Stack, they are indistinct
//A2: The variable lives on the Stack, the instance on the Heap. They are separate entities
//A3: The third one