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| <document> |
| <properties> |
| <title>Introduction</title> |
| </properties> |
| |
| <body> |
| |
| <section name="Introduction"> |
| <p> |
| The <a href="http://java.sun.com/">Java</a> language has become |
| very popular and many research projects deal with further |
| improvements of the language or its run-time behavior. The |
| possibility to extend a language with new concepts is surely a |
| desirable feature, but the implementation issues should be hidden |
| from the user. Fortunately, the concepts of the Java Virtual |
| Machine permit the user-transparent implementation of such |
| extensions with relatively little effort. |
| </p> |
| |
| <p> |
| Because the target language of Java is an interpreted language |
| with a small and easy-to-understand set of instructions (the |
| <em>byte code</em>), developers can implement and test their |
| concepts in a very elegant way. One can write a plug-in |
| replacement for the system's <em>class loader</em> which is |
| responsible for dynamically loading class files at run-time and |
| passing the byte code to the Virtual Machine (see <a |
| href="jvm.html">section 2</a>). |
| Class loaders may thus be used to intercept the loading process |
| and transform classes before they get actually executed by the |
| JVM. While the original class files always remain unaltered, the |
| behavior of the class loader may be reconfigured for every |
| execution or instrumented dynamically. |
| </p> |
| |
| <p> |
| The <font face="helvetica,arial">BCEL</font> API (Byte Code |
| Engineering Library), formerly known as JavaClass, is a toolkit |
| for the static analysis and dynamic creation or transformation of |
| Java class files. It enables developers to implement the desired |
| features on a high level of abstraction without handling all the |
| internal details of the Java class file format and thus |
| re-inventing the wheel every time. <font face="helvetica,arial">BCEL |
| </font> is written entirely in Java and freely available under the |
| terms of the <a href="license.html">Apache Software License</a>. |
| </p> |
| |
| <p> |
| This manual is structured as follows: We give a brief description |
| of the Java Virtual Machine and the class file format in <a |
| href="jvm.html">section 2</a>. <a href="bcel-api.html">Section 3</a> |
| introduces the <font face="helvetica,arial">BCEL</font> API. |
| <a href="application-areas.html">Section 4</a> describes some typical |
| application areas and example projects. The appendix contains code examples |
| that are to long to be presented in the main part of this paper. All examples |
| are included in the down-loadable distribution. |
| </p> |
| </section> |
| |
| </body> |
| |
| </document> |
