Converting Pointer Parameters in C++ to Java

By: Baski

For the most part, it is quite easy to convert a C++ function that uses pointer parameters into its equivalent Java method. Since Java passes all objects by reference, sometimes the conversion simply requires the removal of C++'s pointer operators. For example, consider this C++ program that reverses the signs of a Coord object, which stores a pair of Cartesian coordinates. The function reverseSign( ) is passed a pointer to the Coord object that will be reversed. As you can see, C++'s *, &, and -> pointer operators are used to perform the operation.

// Reverse the signs of a coordinate - C++ version.
#include <iostream>
using namespace std;
class Coord {
public:
int x;
int y;
};

// Reverse the sign of the coordinates.
void reverseSign(Coord *ob) {
ob->x = -ob->x;
ob->y = -ob->y;
}
int main()
{
Coord ob;
ob.x = 10;
ob.y = 20;
cout << "Original values for ob: ";
cout << ob.x << ", " << ob.y << "\\n";
reverseSign(&ob);
cout << "Sign reversed values for ob: ";
cout << ob.x << ", " << ob.y << "\\n";
return 0;
}

This program can be recoded into the following Java version. As you can see, most of the conversion involves the deletion of the C++ pointer operators. Since Java passes objects by reference, changes to the parameter automatically affect the argument.

// Reverse the signs of a coordinate - Java version.
class Coord {
int x;
int y;
};

class DropPointers {
// Reverse the sign of the coordinates.
static void reverseCoord(Coord ob) {
ob.x = -ob.x;
ob.y = -ob.y;
}

public static void main(String args[]) {
Coord ob = new Coord();
ob.x = 10;
ob.y = 20;
System.out.println("Original values for ob: " +
ob.x + ", " + ob.y);
reverseCoord(ob);
System.out.println("Sign reversed values for ob: " +
ob.x + ", " + ob.y);
}
}