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Throughout this book, you ve often used special variables provided by Ruby for various purposes. For example, $! contains a string of the last error message raised in the program, $$ returns the process ID of the current program, and $/ lets you adjust the default line or record separator as used by the gets method. The English library allows you to access Ruby s special variables using names expressed in English, rather than symbols. This makes the variables easier to remember.

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<Application xmlns="http://schemas.microsoft.com/client/2007" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" x:Class="SilverlightApplication1.App"> <Application.Resources> <Style TargetType="TextBlock" x:Key="TextBlockStyle"> <Setter Property="FontFamily" Value="Comic Sans Ms"></Setter> <Setter Property="Text" Value="Click!"></Setter> <Setter Property="Foreground" Value="MediumBlue"></Setter> <Setter Property="FontSize" Value="20"></Setter> </Style> </Application.Resources> </Application>

Managing security very often comes down to the subject/object/action-tuple. The subject is the actor that is trying to take some action on an object. For example, a user may try to access a file, as shown in Figure 1-1.

Enumerated types make the program much easier to write, read, and maintain . With enumerated types, the symbolic name is used throughout the code, and the programmer doesn t have to mentally map the meaning of each hard-coded value (for example, white is 0 or vice versa) . Also, should a symbol s numeric value change, the code can simply be recompiled without requiring any changes to the source code . In addition, documentation tools and other utilities, such as a debugger, can show meaningful symbolic names to the programmer .

What makes Eclipse very appealing to a Java developer is the wealth of plug-ins, both commercial and open source, that exist to make every aspect of development more agile and enjoyable. The rest of the chapter will concentrate on showing some of the plug-ins that I ve found to be the most useful when trying to develop an enterprise Java application. Many of the open source tools used in this book to develop the TechConf sample application provide for integration with the Eclipse platform via plug-ins.

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The field is part of the type s state, as opposed to being part of an object s state . The field is associated with an instance of the type, not the type itself . The field can be written to only by code contained in a constructor method . Code that accessed the field is not subject to some thread-unsafe optimizations that may be performed by the compiler, the CLR, or by hardware . Only the following types can be marked volatile: all reference types, Single, Boolean, Byte, SByte, Int16, UInt16, Int32, UInt32, Char, and all enumerated types with an underlying type of Byte, SByte, Int16, UInt16, Int32, or UInt32 . Volatile fields are discussed in 28, Primitive Thread Synchronization Constructs .

Preprocessor directives are instructions to the C# compiler to perform some action during compilation. There is no equivalent functionality in Java. The term preprocessor directive is misleading because the compilation process does not include a preprocessing step, but the term is a legacy of C/C++ and has remained to avoid confusion. Preprocessor directives are used to