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According to Baldwin, static members can be useful in some situations, but the overuse of static members can lead to problems similar to those experienced in languages that support global variables and global functions.

Revised: Thu Mar 31 15:56:25 CDT 2016

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Table of contents

Preface

This module is one of a series of modules designed to teach you about Object-Oriented Programming (OOP) using Java.

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 Figuresand Listings while you are reading about them.

Figures

  • Figure 1 . Output date and time.
  • Figure 2 . Five seconds later.
  • Figure 3 . Same date and time as before.
  • Figure 4 . A new date and time.
  • Figure 5 . Same date and time as before.
  • Figure 6 . Output from overridden toString method in Date class.

Listings

Preview

Static members

There is another aspect of OOP in Java that I have avoided up to this point in the discussion: static variables and static methods.

Tends to complicate ...

I have avoided this topic because, while not particularly difficult, the existence of static members tends to break up the simple structures that I have discussed in previous modules in this collection.

While static members can be useful in some situations, the existence of static members tends to complicate the overall object-oriented structure of Java.

Avoid overuse of static members

Furthermore, the overuse of static members can lead to problems similar to those experienced in languages like C and C++ that support global variables andglobal functions.

When to use static members

I will discuss the use of static members in this module, and will provide some guidelines for their use.

The class named Class

I will also introduce the class named Class and discuss how it enters into the use of static variables and methods.

Instance members versus class members

I will describe the differences between instance members and class members with particular emphasis being placed on their accessibility.

Three kinds of objects

From a conceptual viewpoint, there are at least three kinds of objects involved in a Java program:

  • Ordinary objects
  • Array objects
  • Class objects

Ordinary objects

All (or at least most) of the discussion up to this point in the collection deals with what I have referred to in the above list as ordinary objects .

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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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