What is a method?
Ans : A method is the basic unit of functionality in an object-oriented languagea body of executable code that belongs to a class and that can be applied to (invoked on) a specific object or the class itself. Methods are the object-oriented counterpart to functions or subroutines. Like a function, a method consists of: • a name • a (possibly empty) list of input names, called parameters, and their types • an (optional) output type, called the return type (the void keyword declares that a method has no return type) • a body of executable code The following code fragment declares a method whose output (of type double) is the average of its two input values (also of type double): double average(double a, double b) { return (a + b) / 2.0; } Because methods belong to classes, you can define a method only in the body of a class definition. Note that the code fragment, however, follows the convention of this book in not showing the enclosing class definition unless relevant. You usually use a
In the terminology of SRB, a method is any executable piece of code that is registered in the MCAT catalog. Methods can be defined to operate on data on the server before being returned to the client. This can be quite efficient in cases where the data object is being reduced by the method (for example, the method selects a subset of the data object based on inputs, such as metadata extractors (FITS, DICOM, etc)). Format converters, such as tiff2gif and tex2ps can also be useful SRB methods.
A method implements behavior, which is defined by [Booch 91, p80]: Behavior is how an object acts and reacts, in terms of its state changes and message passing. A method is a function or procedure which is defined in a class and typically can access the internal state of an object of that class to perform some operation. It can be thought of as a procedure with the first parameter as the object to work on. This object is called the receiver, which is the object the method operates on. An exception exists with C++’s static member functions which do not have a receiver, or “this” pointer. The following are some common notations for invoking a method, and this invocation can be called a message (or message passing, see below): receiver.message_name(a1, a2, a3) receiver message_name: a1 parm1: a2 parm3: a3 Selector would be another good choice for message_name in the above examples, although keywords (or formal parameter names, like named parameters) are considered part of the selector in
