2.10 Java1620: static members

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

This page is included in the following Books:

• ITSE 2321 - Object-Oriented Programming (Java)
• Object-Oriented Programming (OOP) with Java

Table of contents

• Preface
  • Viewing tip
    • Figures
    • Listings
• Preview
• Discussion and sample code
• Summary
• What's next?
• Miscellaneous
• Complete program listing

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

• Listing 1 . Beginning of the class named MyClass01.
• Listing 2 . Signature of the main method.
• Listing 3 . Display some text.
• Listing 4 . Display date information.
• Listing 5 . A five-second delay.
• Listing 6 . Instantiate a new object.
• Listing 7 . Display the new Date object.
• Listing 8 . Accessing class variable via an object.
• Listing 9 . Another new object.
• Listing 10 . Display the date and time.
• Listing 11 . Display date information.
• Listing 12 . Revisiting System.out.println.
• Listing 13 . Complete program listing.

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 .