import javassist.ClassPool; import javassist.CtClass; import javassist.CtField; public class JavassistExample { public static void main(String[] args) throws Exception { ClassPool classPool = ClassPool.getDefault(); CtClass ctClass = classPool.get("com.example.MyClass"); CtField newField = new CtField(CtClass.intType, "newField", ctClass); ctClass.addField(newField); ctClass.writeFile(); System.out.println("Class modified successfully!"); } }