Java Programing

* @see PotatoPeeler * @see PotatoMasher * @author John ‘Spuds’ Smith * @version 1.00, 19 Dec 1996 */ javadoc creates HTML format documentation of classes by reading the source code and the embedded comments. The author and version information is presented in the output, and the @see tags make hypertext links to the appropriate class documentation. The compiler also looks at the doc comments; in particular, it is interested in the @deprecated tag, which means that the method has been declared obsolete and should be avoided in new programs. The compiler generates a warning message whenever it sees the usage of a deprecated feature in your code. Doc comments can appear above class, method, and variable definitions, but some tags may not be applicable to all of these. For example, a variable declaration can contain only a @see tag. Table 4.1 summarizes the tags used in doc comments. Table 4.1, Doc Comment Tags Tag Description Applies to @see Associated class name Class, method, or variable @author Author name Class @version Version string Class @param Parameter name and description Method @return Description of return value Method @exception Exception name and description Method @deprecated Declares an item to be obsolete Class, method, or variable 4.3 Types The type system of a programming language describes how its data elements ( variables and constants) are associated with actual storage. In a statically typed language, like C or C++, the type of a data element is a simple, unchanging attribute that often corresponds directly to some underlying hardware phenomenon, like a register value or a pointer indirection. In a more dynamic language like Smalltalk or Lisp, variables can be assigned arbitrary elements and can effectively change their type throughout their lifetime. A considerable amount of overhead goes into validating what happens in these languages at runtime. Scripting languages like Perl and Tcl achieve ease of use by providing drastically simplified type systems in which only certain data elements can be stored in variables, and values are unified into a common representation, such as strings. Java combines the best features of both statically and dynamically typed languages. As in a statically typed language, every variable and programming element in Java has a type that is known at compile time, so the runtime system doesn’t normally have to check the type validity of assignments while the code is executing. Unlike C or C++, though, Java also maintains runtime information about objects and uses this to allow truly safe runtime polymorphism and casting (using an object as a type other than its declared type). Java data types fall into two categories. Primitive types represent simple values that have built-in functionality in the language; they are fixed elements, such as literal constants and numbers. Reference types (or class types) include objects and arrays; they are called reference types because they are passed “by reference,” as we’ll explain shortly. - 67

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