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Java I/O by Elliotte Rusty Harold

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Conventions Used in This Book

Italic is used for:

Constant width is used for:

  • Code examples and fragments

  • Class, variable, and method names, and Java keywords used within the text

Significant code fragments and complete programs are generally placed in a separate paragraph like this:

InputStream in = new FileInputStream("/etc/mailcap");

When code is presented as fragments rather than complete programs, the existence of the appropriate import statements should be inferred. For example, in the previous code fragment you may assume that java.io.InputStream and java.io.FileInputStream were imported.

Some examples intermix user input with program output. In these cases, the user input will be displayed in bold, but otherwise in the same monospaced font, as in this example from Chapter 17:

D:\JAVA\16>java PortTyper COM2
            at&f
at&f

OK
atdt 321-1444

Most of the code examples in this book are optimized for legibility rather than speed. For instance, consider this getIcon() method from Chapter 13:

public Icon getIcon(File f) {
  
  if (f.getName().endsWith(".zip")) return zipIcon;
  if (f.getName().endsWith(".gz")) return gzipIcon;
  if (f.getName().endsWith(".dfl")) return deflateIcon;
  return null;
}

I invoke the f.getName() method three times, when once would do:

public Icon getIcon(File f) {
  
  String name = f.getName();
  if (name.endsWith(".zip")) return zipIcon;
  if (name.endsWith(".gz")) return gzipIcon;
  if (name.endsWith(".dfl")) return deflateIcon;
  return null;
}

However, this seemed slightly less obvious than the first example. Therefore, I chose the marginally slower form. Other, still less obvious optimizations are also possible, but would only make the code even more obscure. For example:

public Icon getIcon(File f) {

  String name = f.getName();
  String lastDot = name.lastIndexOf('.');
  if (lastDot != -1) {
    String extension = name.substring(lastDot+1);
    if (extension.equals("zip")) return zipIcon;
    if (extension.equals("gz")) return gzipIcon;
    if (extension.equals("dfl")) return deflateIcon;
  }
  return null;
}

I might resort to this form if profiling proved that this method was a performance bottleneck in my application, and this revised method was genuinely faster, but I certainly wouldn’t use it in my first pass at the problem. In general, I only optimize for speed when similar code seems likely to be a performance bottleneck in situations where it’s likely to be used, or when optimizing can be done without negatively affecting the legibility of the code.

Finally, although many of the examples are toys unlikely to be reused, a few of the classes I develop have real value. Please feel free to reuse them or any parts of them in your own code; no special permission is required. Such classes are placed somewhere in the com.macfaq package, generally mirroring the java package hierarchy. For instance, Chapter 2’s NullOutputStream class is in the com.macfaq.io package; its StreamedTextArea class is in the com.macfaq.awt package. When working with these classes, don’t forget that the compiled .class files must reside in directories matching their package structure inside your class path and that you’ll have to import them in your own classes before you can use them.[2] The web page includes a JAR file that can be installed in your class path.

Furthermore, classes not in the default package with main() methods are generally run by passing in the full package-qualified name. For example:

D:\JAVA\ioexamples\04>java com.macfaq.io.FileCopier oldfile newfile


[2] See “The Name Space: Packages, Classes, and Members” in the second edition of David Flanagan’s Java in a Nutshell (O’Reilly & Associates, 1997).

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