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| * ASM: a very small and fast Java bytecode manipulation framework | |
| * Copyright (c) 2000-2005 INRIA, France Telecom | |
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| <body> | |
| Provides a small and fast bytecode manipulation framework. | |
| <p> | |
| The <a href="http://www.objectweb.org/asm">ASM</a> framework is organized | |
| around the {@link org.objectweb.asm.ClassVisitor ClassVisitor}, | |
| {@link org.objectweb.asm.FieldVisitor FieldVisitor} and | |
| {@link org.objectweb.asm.MethodVisitor MethodVisitor} interfaces, which allow | |
| one to visit the fields and methods of a class, including the bytecode | |
| instructions of each method. | |
| <p> | |
| In addition to these main interfaces, ASM provides a {@link | |
| org.objectweb.asm.ClassReader ClassReader} class, that can parse an | |
| existing class and make a given visitor visit it. ASM also provides | |
| a {@link org.objectweb.asm.ClassWriter ClassWriter} class, which is | |
| a visitor that generates Java class files. | |
| <p> | |
| In order to generate a class from scratch, only the {@link | |
| org.objectweb.asm.ClassWriter ClassWriter} class is necessary. Indeed, | |
| in order to generate a class, one must just call its visit<i>XXX</i> | |
| methods with the appropriate arguments to generate the desired fields | |
| and methods. See the "helloworld" example in the ASM distribution for | |
| more details about class generation. | |
| <p> | |
| In order to modify existing classes, one must use a {@link | |
| org.objectweb.asm.ClassReader ClassReader} class to analyze | |
| the original class, a class modifier, and a {@link org.objectweb.asm.ClassWriter | |
| ClassWriter} to construct the modified class. The class modifier | |
| is just a {@link org.objectweb.asm.ClassVisitor ClassVisitor} | |
| that delegates most of the work to another {@link org.objectweb.asm.ClassVisitor | |
| ClassVisitor}, but that sometimes changes some parameter values, | |
| or call additional methods, in order to implement the desired | |
| modification process. In order to make it easier to implement such | |
| class modifiers, ASM provides the {@link org.objectweb.asm.ClassAdapter | |
| ClassAdapter} and {@link org.objectweb.asm.MethodAdapter MethodAdapter} | |
| classes, which implement the {@link org.objectweb.asm.ClassVisitor ClassVisitor} | |
| and {@link org.objectweb.asm.MethodVisitor MethodVisitor} interfaces by | |
| delegating all work to other visitors. See the "adapt" example in the ASM | |
| distribution for more details about class modification. | |
| <p> | |
| The size of the core ASM library, <tt>asm.jar</tt>, is only 42KB, which is much | |
| smaller than the size of the | |
| <a href="http://jakarta.apache.org/bcel">BCEL</a> library (504KB), and than the | |
| size of the | |
| <a href="http://serp.sourceforge.net">SERP</a> library (150KB). ASM is also | |
| much faster than these tools. Indeed the overhead of a load time class | |
| transformation process is of the order of 60% with ASM, 700% or more with BCEL, | |
| and 1100% or more with SERP (see the <tt>test/perf</tt> directory in the ASM | |
| distribution)! | |
| @since ASM 1.3 | |
| </body> | |
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