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20<document>
21  <properties>
22    <title>Introduction</title>
23  </properties>
24
25  <body>
26
27  <section name="Introduction">
28    <p>
29      The <a href="http://java.sun.com/">Java</a> language has become
30      very popular and many research projects deal with further
31      improvements of the language or its run-time behavior. The
32      possibility to extend a language with new concepts is surely a
33      desirable feature, but the implementation issues should be hidden
34      from the user. Fortunately, the concepts of the Java Virtual
35      Machine permit the user-transparent implementation of such
36      extensions with relatively little effort.
37    </p>
38
39    <p>
40      Because the target language of Java is an interpreted language
41      with a small and easy-to-understand set of instructions (the
42      <em>byte code</em>), developers can implement and test their
43      concepts in a very elegant way. One can write a plug-in
44      replacement for the system's <em>class loader</em> which is
45      responsible for dynamically loading class files at run-time and
46      passing the byte code to the Virtual Machine (see <a
47      href="jvm.html">section 2</a>).
48      Class loaders may thus be used to intercept the loading process
49      and transform classes before they get actually executed by the
50      JVM. While the original class files always remain unaltered, the
51      behavior of the class loader may be reconfigured for every
52      execution or instrumented dynamically.
53    </p>
54
55    <p>
56      The <font face="helvetica,arial">BCEL</font> API (Byte Code
57      Engineering Library), formerly known as JavaClass, is a toolkit
58      for the static analysis and dynamic creation or transformation of
59      Java class files. It enables developers to implement the desired
60      features on a high level of abstraction without handling all the
61      internal details of the Java class file format and thus
62      re-inventing the wheel every time. <font face="helvetica,arial">BCEL
63    </font> is written entirely in Java and freely available under the
64      terms of the <a href="license.html">Apache Software License</a>.
65    </p>
66
67    <p>
68      This manual is structured as follows: We give a brief description
69      of the Java Virtual Machine and the class file format in <a
70            href="jvm.html">section 2</a>. <a href="bcel-api.html">Section 3</a>
71      introduces the <font face="helvetica,arial">BCEL</font> API.
72      <a href="application-areas.html">Section 4</a> describes some typical
73      application areas and example projects. The appendix contains code examples
74      that are to long to be presented in the main part of this paper. All examples
75      are included in the down-loadable distribution.
76    </p>
77  </section>
78
79  </body>
80
81</document>