2.7 Jb0130: java oop: a gentle introduction to methods in java  (Page 2/5)

A method provides a better way

The better way is to create a separate program module that has the ability to calculate the square root and make that module available for use as a helper to your main program each time your main program needs to calculate a square root. In Java, this separate program module is called a method .

Standard methods

The Java programming language contains a large number of methods (in the class libraries) that are already available for your use. (Later, I will illustrate the use of a standard method for calculating the square root of a number.)

In addition to the standard methods that are already available, if you need a method to perform some function and there is no standard method already available to perform that function, you can write your own method.

Passing parameters

Make the method general

Normally, when designing and writing a method such as one that can calculate the square root of a number, it is desirable to write it in such a way that it can calculate the square root of any number (as opposed to only one specific number) . This is accomplished through the use of something called parameters .

The process of causing a method to be executed is commonly referred to as calling the method .

Pass me the number please

When your program calls the square-root method, it will need to tell the method the value for which the square root is needed.

In general, many methods will require that you provide certain kinds of information when you call them. The code in the method needs this information to be able to accomplish its purpose.

Passing parameters

This process of providing information to a method when you call it is commonly referred to as passing parameters to the method. For the square-root method, you need to pass a parameter whose value is the value of the number for which you need the square root.

Returning values

A method will usually

• perform an action
• send back an answer. or
• some combination of the two

Performing an action

An example of a method that performs an action is the standard method named println . We used the println method in an earlier module to cause information to be displayed on the computer screen. This method does not need to send back an answer, because that is not the objective of the method. The objective is simply to display some information.

Sending back an answer

On the other hand, a method that is designed to calculate the square root of a number needs to be able to send the square-root value back to the program that called the method. After all, it wouldn't be very useful if the method calculated the square root and then kept it a secret. The process of sending back an answer is commonly referred to as returning a value .

Returned values can be ignored

Methods can be designed in such a way that they either will or will not return a value. When a method does return a value, the program that called the method can either pay attention to that value and use it for some purpose, or ignore it entirely.

For example, in some cases where a method performs an action and also returns a value, the calling program may elect to ignore the returned value. On the other hand, if the sole purpose of a method is to return a value, it wouldn't make much sense for a program to call that method and then ignore the value that is returned (although that would be technically possible) .