![]() ![]() Always remember! Whenever reflection is used, the security of the application is compromised. It is an advanced feature that should only be used by programmers or developers who have a good knowledge of the basics of the language. Conclusionīecause of the above-mentioned cons, it is generally advisable to avoid using reflection. Therefore, the operations performed by reflections are usually slow. Since the types in reflection are resolved dynamically, JVM (Java Virtual Machine) optimization cannot take place. For example, if one access the private members of a class and sets null value to it, then the other user of the same class can get the NullReferenceException, and this behaviour is not expected.Īnother demerit is the overhead in performance. getDeclaredMethod() : To create an object of method to be invoked. Thus, reflection may leak important data to the outside world, which is dangerous. The required classes for reflection are provided under package. The following example demonstrates how to get the instance of Class class in different. ![]() It is possible to access the private methods and fields of a class using reflection. Using Java Reflection we can inspect a class, interface, enum. It helps in the creation of Visual Development Environments and class browsers which provides aid to the developers to write the correct code.Ĭons: Using reflection, one can break the principles of encapsulation. ![]() It is also possible to call methods, instantiate a clear or to set the value of fields using reflection. Pros: Inspection of interfaces, classes, methods, and fields during runtime is possible using reflection, even without using their names during the compile time. While the reflection provides a lot of advantages, it has some disadvantages too. Java reflection should always be used with caution. Let's see the simple example of forName() method. This month I'll take a look at the Java Reflection API. It should be used if you know the fully qualified name of class.This cannot be used for primitive types. That example is a form of static introspection.There are 3 ways to get the instance of Class class. Returns the total number of constructors of this class.ġ1) public Method getDeclaredMethod(String name,Class parameterTypes)throws NoSuchMethodException,SecurityException Further, I showed that with the addition of a class loader, those classes could be loaded into the running environment and executed. Returns the total number of methods of this class.ġ0) public Constructor getDeclaredConstructors()throws SecurityException Returns the total number of fields of this class.ĩ) public Method getDeclaredMethods()throws SecurityException Loads the class and returns the reference of Class class.ģ) public Object newInstance()throws InstantiationException,IllegalAccessExceptionĨ) public Field getDeclaredFields()throws SecurityException (JavaReflectionExample2.java:17)Īt 2.main(JavaReflectionExample2.Commonly used methods of Class class: MethodĢ) public static Class forName(String className)throws ClassNotFoundException The actual error message (stack trace) is as follows: Here's the line of code that actually throws the exception:īecause this method ( fooMethod) doesn't exist, a NoSuchMethodException is thrown. In this example I intentionally create a NoSuchMethodException by trying to instantiate a method named fooMethod on the class. Method m = c.getDeclaredMethod("fooMethod", paramTypes) To perform reflection, you can use the object of a class. Java has a class named class that collects and stores all information about classes and objects, this class helps facilitate the ability to use reflection. The following example Java class shows how this NoSuchMethodException can be generated: Java reflection is an API used to inspect and modify Java classes, fields, methods, and constructors at runtime. Java exception FAQ: What is a Java NoSuchMethodException?Īnswer: Using Java, you can get a NoSuchMethodException when you're using reflection and try to dynamically use a method on a class, and the method does not actually exist.
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