Two ways to save data in programming
When you put data into the variable, the programming language has 2 choices to save the data.
- Save data into heap memory and then keep the address of the memory in the stack memory.
- save data into stack memory.
Why there are two ways?
Stack memory is much faster than heap memory. However, the stack memory has limited space. Thus, a computer is designed to save static data(temporary use, calculate damage when you hit monsters) in stack memory and save dynamic data(use again, you learn a new skill in the game.) in heap memory.
What is pass-by-value
- When using the method, pass the value only. Thus, if the input data changes, the original variable’s data will not change.
- Save data into stack memory.
What is pass-by-reference
- When using the method, pass the value’s address. Thus, if the input data changes, the original variable’s data will be changed.
- Save data into heap memory and then keep the address of the memory in the stack memory.
Java Vs. C++
Java is pass-by-value
However, when using the object, the object address will be used in the method. In other words, the original variable’s data will be changed.
public class Main {
public static void main(String[] args) {
int a = 10;
System.out.println("A is " + a); // 10
increaseNum(a);//pass the value only
System.out.println("A is " + a); // 10
Student A = new Student(24);
System.out.println(A.getAge()); // 24
increaseAge(A);// pass the object address
System.out.println(A.getAge()); // 34
}
public static void increaseNum(int input) {
int temp = input;
temp++;
}
public static void increaseAge(Student input) {
input.setAge(input.getAge() + 10);
}
}
public class Student {
int age;
public Student(int age) {
this.age = age;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
Pass-by-Value vs Pass-by-Reference in C++
C++ allows programmers to choose between pass-by-value and pass-by-reference when passing variables to functions or methods, giving them greater flexibility and control over how their programs handle data.
#include <iostream>
using namespace std;
class Student {
private:
int age;
public:
void setAge(int s) {
age = s;
}
int getAge() {
return age;
}
};
void increaseAge(Student i) {
i.setAge(i.getAge()+10);
}
void increaseAge2(Student &i) {
i.setAge(i.getAge()+10);
}
void increaseNum(int i) {
i++;
}
void increaseNum2(int &i) {
i++;
}
int main(void) {
int a = 10;
cout << "A is " << a << endl; // 10
increaseNum(a); //pass the value
cout << "A is " << a << endl; // 10
increaseNum2(a); //pass by reference
cout << "A is " << a << endl; // 11
Student B;
B.setAge(20);
cout << B.getAge() << "\\\\n"; // 20
increaseAge(B); //pass the value
cout << B.getAge() << "\\\\n"; // 20
increaseAge2(B); //pass by reference
cout << B.getAge() << "\\\\n"; // 30
return 0;
}
