The ASM framework is organized around the {@link mz.asm.ClassVisitor ClassVisitor}, {@link mz.asm.FieldVisitor FieldVisitor}, {@link mz.asm.MethodVisitor MethodVisitor} and {@link mz.asm.AnnotationVisitor AnnotationVisitor} abstract classes, which allow one to visit the fields, methods and annotations of a class, including the bytecode instructions of each method.

In addition to these main abstract classes, ASM provides a {@link mz.asm.ClassReader ClassReader} class, that can parse an existing class and make a given visitor visit it. ASM also provides a {@link mz.asm.ClassWriter ClassWriter} class, which is a visitor that generates Java class files.

In order to generate a class from scratch, only the {@link mz.asm.ClassWriter ClassWriter} class is necessary. Indeed, in order to generate a class, one must just call its visitXxx methods with the appropriate arguments to generate the desired fields and methods.

In order to modify existing classes, one must use a {@link mz.asm.ClassReader ClassReader} class to analyze the original class, a class modifier, and a {@link mz.asm.ClassWriter ClassWriter} to construct the modified class. The class modifier is just a {@link mz.asm.ClassVisitor ClassVisitor} that delegates most of the work to another {@link mz.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, the {@link mz.asm.ClassVisitor ClassVisitor} and {@link mz.asm.MethodVisitor MethodVisitor} classes delegate by default all the method calls they receive to an optional visitor. @since ASM 1.3