C++ & Java - overloading operator

Question

I have a difficult to understand the subject of overloading operator in C++ and Java.

For example, I define a new class Fraction:

class Fraction { 
public: 
    Fraction (int top, int bottom) { t = top; b = bottom; } 
    int numerator() { return t; } 
    int denominator() { return b; } 
private: 
    int t, b; 
};

and I want to overload the operator << for printing Fraction. How I do it? I need to overload it inside Class Fraction or outside Class Fraction?

In java - Is it possible to overload operator? How I can do it there (for example, I want to overload the operator +).

If there is a metrial about this subject, It will be great.

in Java you can't overload operators Here is an example how to overload `<<` : http://www.codeproject.com/KB/cpp/cfraction.aspx — Andrei Sfat, Jun 18 '11 at 17:48
You can't overload operators in Java, but the + and += operators are overloaded by default for String concatenation. That's the only exception. — Marcelo, Jun 18 '11 at 17:51
For the C++ side of it, look at this question: http://stackoverflow.com/questions/4421706/operator-overloading — David Rodríguez - dribeas, Jun 18 '11 at 17:54

score 5 · Answer 1 · answered Jun 18 '11 at 17:49

5

In java - Is it possible to overload operator?

No, Java has no operator overloading.

answered Jun 18 '11 at 17:49

Bart Kiers

166,582
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Avada Kedavra · Accepted Answer · 2011-06-18T18:07:14.643

For C++: Overloading the << Operator on msdn

// overload_date.cpp
// compile with: /EHsc
#include <iostream>
using namespace std;

class Date
{
    int mo, da, yr;
public:
    Date(int m, int d, int y)
    {
        mo = m; da = d; yr = y;
    }
    friend ostream& operator<<(ostream& os, const Date& dt);
};

ostream& operator<<(ostream& os, const Date& dt)
{
    os << dt.mo << '/' << dt.da << '/' << dt.yr;
    return os;
}

int main()
{
    Date dt(5, 6, 92);
    cout << dt;
}

So as answer to "I need to overload it inside Class Fraction or outside Class Fraction?" You declare the function as a friend of the class so that the std::osteam object can access its private data. The function, however, is defined outside of the class.

score 1 · Answer 3 · edited Jun 18 '11 at 18:50

1

In c++ you can overload an operator for the class that it is applied to. In your case, you'd have

class Fraction { 
public: 
    Fraction (int top, int bottom) { t = top; b = bottom; } 
    int numerator() { return t; } 
    int denominator() { return b; } 
    inline bool operator << (const Fraction &f) const
    {
        // do your stuff here
    }

private: 
    int t, b; 
};

edited Jun 18 '11 at 18:50

Andrei Sfat

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answered Jun 18 '11 at 17:55

Steve Kawolsky

64
2

score 1 · Answer 4 · edited May 23 '17 at 12:04

To give you a complete answer provided by myself, Marcelo and David Rodríguez - dribeas in the comments:

in Java you can't overload operators

to complete my answer:

[...], but the + and += operators are overloaded by default for String concatenation. That's the only exception.

@Marcelo

And about the C++ overloading operators:

For the C++ side of it, look at this question: stackoverflow.com/questions/4421706/operator-overloading

@David Rodríguez - dribeas

C++ & Java - overloading operator

4 Answers4