<dependency> <groupId>org.javassist</groupId> <artifactId>javassist</artifactId> <version>3.28.0-GA</version> </dependency> import org.javassist.CtClass; CtClass ctClass = CtNewClass.make("com.example.MyClass", ClassPool.getDefault()); CtMethod newMethod = new CtMethod(void.class, "newMethod", new CtClass[] { }, null, null); ctClass.addMethod(newMethod); ClassPool classPool = ClassPool.getDefault(); CtClass loadedClass = classPool.get("com.example.MyClass"); MyClass obj = (MyClass) loadedClass.newInstance(); obj.newMethod(); import org.javassist.CtClass; import org.javassist.CtMethod; public class JavassistExample { public static void main(String[] args) throws Exception { ClassPool classPool = ClassPool.getDefault(); CtClass ctClass = classPool.get("com.example.MyClass"); CtMethod newMethod = new CtMethod(void.class, "newMethod", new CtClass[] { }, null, null); ctClass.addMethod(newMethod); ClassPool classPool2 = ClassPool.getDefault(); CtClass loadedClass = classPool2.get("com.example.MyClass"); MyClass obj = (MyClass) loadedClass.newInstance(); obj.newMethod(); } }