2.7 Jb0130: java oop: a gentle introduction to methods in java

Revised: Sun Mar 27 20:13:16 CDT 2016

This page is included in the following Books:

• Programming Fundamentals with Java
• Object-Oriented Programming (OOP) with Java

Table of contents

• Preface
  • General
  • Prerequisites
  • Viewing tip
    • Listings
• Discussion and sample code
  • Introduction
  • Standard methods
  • Passing parameters
  • Returning values
  • Writing your own methods
  • Sample program
    • Interesting code fragments
• Run the program
• Complete program listings
• Miscellaneous

Preface

General

This module is part of a collection of modules designed to help you learn to program computers.

It provides a gentle introduction to Java programming methods.

Prerequisites

In addition to an Internet connection and a browser, you will need the following tools (as a minimum) to work through the exercises in these modules:

• The Sun/Oracle Java Development Kit (JDK) (See (External Link) )
• Documentation for the Sun/Oracle Java Development Kit (JDK) (See (External Link) )
• A simple IDE or text editor for use in writing Java code.

The minimum prerequisites for understanding the material in these modules include:

• An understanding of algebra.
• An understanding of all of the material covered in the earlier modules in this collection.

Viewing tip

I recommend that you open another copy of this document in a separate browser window and use the following links to easily find and view the listings while you are reading about them.

Listings

• Listing 1 . The price of beans.
• Listing 2 . Compute the square root of the price of beans.
• Listing 3 . Display the square root value.
• Listing 4 . Calling the same methods again.
• Listing 5 . The program named SqRt01.
• Listing 6 . A batch file for compiling and running the program named SqRt01.

Discussion and sample code

Introduction

Methods have been used in computer programming since the early days of programming. Methods are often called functions, procedures, subroutines, and various other names.

Calculate the square root

Suppose that your program needs to calculate the square root of a number. Referring back to your high-school algebra book, you could refresh your memory on how to calculate a square root. Then you could construct the algorithm describing that process.

Having the algorithm available, you could write the code to calculate the square root and insert it into your program code. Then you could compile, and run your program. If you did it all correctly, your program should calculate the square root. (For reasons that will become apparent later, I will refer to the code that you inserted as in-line code.)

Oops, need to do it all over again

Suppose that further on in your program you discover that you need to calculate the square root of another number. And later, you discover that you need to calculate the square root of still another number. Obviously, with a few changes, you could copy your original code and insert it as in-line code at each location in your program where you need to calculate the square root of a number.

Is there a better way?

However, after doing this a few times, you might start asking if there is a better way. The answer is "yes, there is a better way."