Chapter 1. Introduction

The trouble with doing something right the first time is that nobody appreciates how difficult it was.

—Fortune

There is a general perception that Java programs are slow. Part of this perception is pure assumption: many people assume that if a program is not compiled, it must be slow. Part of this perception is based in reality: many early applets and applications were slow, because of nonoptimal coding, initially unoptimized Java Virtual Machines (VMs), and the overhead of the language.

In earlier versions of Java, you had to struggle hard and compromise a lot to make a Java application run quickly. More recently, there have been fewer reasons why an application should be slow. The VM technology and Java development tools have progressed to the point where a Java application (or applet, servlet, etc.) is not particularly handicapped. With good designs and by following good coding practices and avoiding bottlenecks, applications usually run fast enough. However, the truth is that the first (and even several subsequent) versions of a program written in any language are often slower than expected, and the reasons for this lack of performance are not always clear to the developer.

This book shows you why a particular Java application might be running slower than expected, and suggests ways to avoid or overcome these pitfalls and improve the performance of your application. In this book I've gathered several years of tuning experiences in one place. I hope you will find it useful in making your Java application, applet, servlet, and component run as fast as you need.

Throughout the book I use the generic words "application" and "program" to cover Java applications, applets, servlets, beans, libraries, and really any use of Java code. Where a technique can be applied only to some subset of these various types of Java programs, I say so. Otherwise, the technique applies across all types of Java programs.