Operator Overloading (C# vs Java)
Like C++, C# allows you to overload operators for use on your own classes. This makes it possible for a user-defined data type to look as natural and be as logical to use as a fundamental data type. For example, you might create a new data type called ComplexNumber to represent a complex number, and provide methods that perform mathematical operations on such numbers using the standard arithmetic operators, such as using the + operator to add two complex numbers.
To overload an operator, you write a function that has the name operator followed by the symbol for the operator to be overloaded. For instance, this is how you would overload the + operator:
public static ComplexNumber operator+(ComplexNumber a, ComplexNumber b)
All operator overloads are static methods of the class. Also be aware that if you overload the equality (==) operator, you must overload the inequality operator (!=) as well. The < and > operators, and the <= and >= operators should also be overloaded in pairs.
The full list of operators that can be overloaded is:
Unary operators: +, -, !, ~, ++, --, true, false
Binary operators: +, -, *, /, %, &, |, ^, <<, >>, ==, !=, >, <, >=, <=
The following code example creates a ComplexNumber class that overloads the + and - operators:
public class ComplexNumber
{
private int real;
private int imaginary;
public ComplexNumber() : this(0, 0) // constructor
{
}
public ComplexNumber(int r, int i) // constructor
{
real = r;
imaginary = i;
}
// Override ToString() to display a complex number in the traditional format:
public override string ToString()
{
return(System.String.Format("{0} + {1}i", real, imaginary));
}
// Overloading '+' operator:
public static ComplexNumber operator+(ComplexNumber a, ComplexNumber b)
{
return new ComplexNumber(a.real + b.real, a.imaginary + b.imaginary);
}
// Overloading '-' operator:
public static ComplexNumber operator-(ComplexNumber a, ComplexNumber b)
{
return new ComplexNumber(a.real - b.real, a.imaginary - b.imaginary);
}
}
This class enables you to create and manipulate two complex numbers with code such as this:
class TestComplexNumber
{
static void Main()
{
ComplexNumber a = new ComplexNumber(10, 12);
ComplexNumber b = new ComplexNumber(8, 9);
System.Console.WriteLine("Complex Number a = {0}", a.ToString());
System.Console.WriteLine("Complex Number b = {0}", b.ToString());
ComplexNumber sum = a + b;
System.Console.WriteLine("Complex Number sum = {0}", sum.ToString());
ComplexNumber difference = a - b;
System.Console.WriteLine("Complex Number difference = {0}", difference.ToString());
}
}
As the program demonstrates, you can now use the plus and minus operators on objects belonging to your ComplexNumber class quite intuitively. Here is the output you would get:
Complex Number a = 10 + 12i
Complex Number b = 8 + 9i
Complex Number sum = 18 + 21i
Complex Number difference = 2 + 3i
Java does not support operator overloading, although internally it overloads the + operator for string concatenation.
See Also
Tasks
Reference
Overloadable Operators (C# Programming Guide)