Java reflection get subclasses Here is an example: Class aClass = //obtain class object Method[] methods = aClass. When working with subclass parameters, it is vital to ensure that the method you are trying to retrieve is compatible with the subclass type. Learn how to manipulate classes during runtime for flexible and extensible applications. If you're wondering why there is the need to do such madness :), it's because sometimes during unit testing it's handy to set private variables to bogus values for failure testing, etc. In that case, put an abstract method on the Customer class and concrete implementations in the subclasses. Understanding how to find classes that extend a particular base class is essential for scenarios such as implementation scanning, plugin systems, dependency injection frameworks, or even simply identifying objects dynamically in your applications. The Service Provider mechanism is the conventional means to enumerate implementations of a pluggable service, and has become more established with the introduction of Project Jigsaw (modules) in Java 9. Then how can I find class A using reflection in Java? Are there any methods present in Java reflection to get all super classes? Learn how to get all declared subclasses at runtime in Java. class literal actually represents an object of type java. myapp; public cl May 29, 2024 · Understanding how to find all classes within a specific package in Java is crucial for many development tasks, particularly when working with large projects that contain numerous classes. getSubTypesOf(Action. The utility comes when you have a parent class and multiple subclasses, and we want to determine the actual type of the object during deserialization Discover how to utilize Java Reflection to find fields of a subclass effectively, with examples and common pitfalls. Nov 10, 2013 · I'm writing a library that uses reflection to find and call methods dynamically. ) Apr 13, 2015 · In the main class it should be possible to instantiate and run every subclass of Device at runtime by calling everyone's 'run' method. The superclass should not even know of the existence of the subclass, much less perform operations based on the fully qualified name of the subclass. class form. getSubTypesOf(MyClass. The benefit of this is to allow users to simply put new Device files into the package and said files will run automatically without having to edit the main class. Java Reflection is a powerful feature that allows you to inspect classes, interfaces, fields, and methods at runtime, regardless of their access modifiers. Learn how to use each approach to make an informed decision for your project. Method. Aug 3, 2022 · Java Reflection for Annotations Reflection in Java Reflection in Java is a very powerful concept and it’s of little use in normal programming but it’s the backbone for most of the Java, J2EE frameworks. In this article, we discuss the accessibility of protected members in different cases. I need to do this in the given package only, i. Jan 16, 2024 · As we know, in the Java world, annotation is a very useful way of obtaining meta information about classes and methods. However, as easy Java generics seem at first glance, as quickly a programer can get lost with this feature. Class representing the runtime classes of c and d, and then we test to see that d ’s runtime class is a subclass of c ’s runtime representation. Feb 15, 2024 · This text explains how to load and reload classes dynamically in Java. Java: Accessing private fields of superclass through reflection You use Class. values() method, because I don't want to collect them manually. forName (class_name) to get the class name. getDeclaredField and AccessibleObject. Jun 17, 2015 · Is there a way to get/set private variables using reflection? (I've done it in C#, but this is the first time I've tried it in Java). So whenever you use generics, the compiler puts all those "generic" inherited methods in the subclass. Retrieving Class Objects The entry point for all reflection operations is java. If you do need operations based on what the exact class is, and can't perform the necessary function by inheritance, you should do something along these lines: May 3, 2017 · Java Reflection get only methods of subclass (without equals, hashcode etc) Asked 8 years, 2 months ago Modified 7 years, 2 months ago Viewed 2k times Feb 6, 2009 · Is it possible to find all classes or interfaces in a given package? (Quickly looking at e. Now, we use methods getClass and isAssignableFrom from Java Reflection to obtain an instance of java. (So these are fields that "C" and "B" can see, but not "A". Project Setup This reflection Java tutorial describes using reflection for accessing and manipulating classes, fields, methods, and constructors 18 I have a 2 POJO classes with getters and setters,now i am trying to get all the class instance variables of that class. Using this API prevents adding a third-party library to our project. I just checked: when I removed the generic related code (the <T> part) from the superclass and the reflection code gave me exactly two methods in the subclass even though it Mar 21, 2022 · 0 Let's say you're making a general reflection class. Source: dev. Given just an object, a method name, and a parameter list, I need to call the given method as though the method cal May 30, 2024 · In summary, finding subclasses of a given class in Java necessitates a careful, methodical approach, relying heavily on classpath scanning and reflection capability. Next step would be to get the constructor and you can do Class. invoke; in particular, this section: Oct 23, 2024 · Retrieving Inner Classes Using Reflection in Java Reflection is a powerful feature in Java that allows developers to inspect and manipulate classes, fields, methods, and constructors at runtime. Java runtime metadata analysis. I think , however, the real issue is what is it you're ultimately trying to achieve, and can it be done more easily using conventional techniques. isAssignableFrom(subClass); Docs: Determines if the class or interface represented by this Class object is either the same as, or is a superclass or superinterface of, the Jul 7, 2024 · Java’s Reflection API is a powerful feature that allows programs to examine and manipulate the structure and properties of objects at runtime. See this JavaWorld tip for a technique to do this. But there's no way to easily identify subclasses of a class. Class Loaders Short answer to your question Is there a way to find out the derived class's name from a base class object? no, the super-class has no way of telling the name/type of a sub-class. This guide covers concepts, code examples, and troubleshooting tips. May 15, 2014 · Given the following snippet: Set<Class<? extends MyClass>> allClasses = new Reflections("mypackage"). isAssignableFrom() might help in this regards. Neither performant nor too reliable. Is there a way to do so? This reflection Java tutorial describes using reflection for accessing and manipulating classes, fields, methods, and constructors java reflection get all fields and corresponding values of generic object including parent class Java Reflection Get all fields of this class and parent class Get all subclasses in the same package (including subcales) according to the parent class Obtain the fields of the entity class through reflection (including the parent class) Java gets the class field, including fields in the parent In Java, you can leverage the reflection API to check if a class is a subclass of another class. , not in the subpackages. Mar 4, 2014 · My hope, is that with this, i will be able to get all the declared fields of the SubClass ONLY, regardless of the SubClass type. So, each subclass sho If you have logic that is specific to a subclass, it belongs in that subclass. This can be really handy, especially if you’re trying to make things easier for future programmers to add more functionality in the future without having to reinvent the entire process. In both cases you've created a dependency on the fields of the class and won't be able to change those fields freely in the future. Field. I am trying to do a static find method that is only in the parent class. For a public class Student extends Emp{ private int marks; //setters and getters } is there anyway to get the fields of a subclass using super class using java Reflection? I need to get Student fields using Emp instance. Java Reflection is a powerful API that allows us to inspect and manipulate classes, methods, fields, and other components at runtime. Nov 1, 2021 · Is there a way to get a collection of instances of subclasses, which are permitted in sealed class? It would be nice to have something similar to Enum. It gets class properties, sub class properties and it's values. Now I would like to create a reflection-method that basically copies all fields that are identical (by name and type) from class A to class CopyA. This article will delve into the To retrieve a list of all the classes loaded in the JVM from a specific package and their subclasses, you can use the Java Reflection API alongside the ClassLoader. Possible Duplicate: How do you find all subclasses of a given class in Java? Hi, I would like to get a list of classes that implement an interface in Java at runtime so I can do a lookup service I'm playing around with Java's reflection API and trying to handle some fields. Generally speaking, type erasure means that all generic type information about a Java class is lost during Jan 8, 2024 · The Java Reflection API provides several ways to check whether an object or a class implements an interface. Recently I had created a series of classes that each Sep 27, 2023 · Explore the choice between Java Jackson @JsonSubTypes and Reflections for achieving polymorphic deserialization in Java. I provided an example in another answer. Feb 1, 2019 · via GIPHY Reflection I’ve talked about reflection a couple of times before. This Learn how to dynamically create subclasses in Java using reflection and other advanced programming techniques. Method dispatching in java always considers the run-time type of the object, even when using reflection. Is there a way to retrieve such information with reflection or any other tool? Jun 4, 2014 · Further to the question posted here: Can you find all classes in a package using reflection? I started using the Reflections library to find all classes that subclass a given type. Within that method in "A", I want to use reflection to find protected fields of the object that are defined in class "B". Mar 22, 2019 · You should not use getClass() together with getDeclaredField, as this will break when there are subclasses. Jan 8, 2024 · Learn how to configure the Reflections library and use it in your Java projects Learn how to utilize Java Reflection to access field values from subclasses. Apr 11, 2025 · I tried your logic. With the instance of the class, using reflection API you can get information about constructors, fields, methods, annotations of the class. This section also covers how you can discover methods in a class. forName() and Class. This process allows you to read or modify fields of a superclass from a subclass, even if those fields are designated as private. The Java getMethod () function, part of the reflection API, allows you to obtain a Method object that reflects the specified public member method of the class or interface represented by a Class object. Some of the frameworks that use java reflection are: JUnit - uses reflection to parse @Test annotation to get the test methods and then Apr 21, 2016 · This text explains how to introspect fields of classes, and get/set them at runtime using Java Reflection Spring Framework - How to find all subclasses in Java? Spring Framework org. DynamoDBTypeConverter ). To get to these classes, it is necessary to invoke appropriate methods on Class. reflect package. Jan 16, 2024 · In this tutorial, we will explore Java reflection, which allows us to inspect and/or modify runtime attributes of classes, interfaces, fields and methods. getConstructor (null) assuming that there isn't any args. Aug 24, 2024 · The Reflection Field class represents each field of a class or interface, and it contains properties such as field name and field value. Unlike direct comparisons for non-derived classes, you can use the `isAssignableFrom ()` method to simplify this task. Class containing protected method: package com. Is there a simple way of doing this? I fear not. public enum state implements EnumInterface{ Accessing private inherited fields in Java requires a combination of reflection and access control manipulation. Apr 27, 2011 · I have a class called MyClass. See the javadoc for Method. Using reflection, we can obtain information about classes and their members, create instances, and invoke methods dynamically. values() function, which is bad because we heavily rely on that functionality. Class class is the entry point for all reflection operations. g. Jun 29, 2001 · Java Reflection provides a lot of information about a given class at runtime; you can easily know all its super classes, implemented interfaces, methods, constructors, fields, and so on. When subclass is instantiated, I need to access its members through reflection. reflect. It allows you to dive deep into a type and get out information at run time. oracle. Inspecting classes is often the first thing you do when using Reflection. 5 days ago · Learn how to get the fields of a class using reflection, including inherited fields Oct 16, 2008 · In addition, I wanted to highlight that you can never get reliably ALL classes implementing an interface, as it is trivial to manufacture a new one out of the thin air at any time. Reflection in Java allows you to inspect and manipulate classes, interfaces, fields, methods, and constructors at runtime Jan 17, 2019 · Sure, I have do some research like package scan, reflection of java, gson and so on. Not validation attributes that I am interested and whether valid or not logic. Java Reflection is a powerful feature that allows inspection and manipulation of classes at runtime. Use the ServiceLoader in Java 6, or implement your own in earlier versions. Feb 28, 2022 · Sealed classes show us which subclasses they permitted. Jan 14, 2011 · The Java reflection API does not have a method that directly gives what you want, but it does expose all the basic information needed to be able to calculate it with Field. Anyway, I assume you are looking for Class. This text will get into more detail about the Java Method object. newInstance() to create any class. ) Dec 17, 2020 · Using solely kotlin-reflect ? There is none. Get step-by-step guidance and code examples. class); The library recursively search for all the classes extending MyClass in the given package and subpackages. In this tutorial, we’re going to discuss scanning Java annotations at runtime. It allows us to deserialize a JSON into a hierarchy of Java objects, even when the specific type is not known at compile time. getSuperclass, Class. (e. com Apr 16, 2020 · If you have plugins (or any other runtime metaprogramming facilities) you cannot dynamically know all the subclasses of a given class, because that set will vary with time, since a freshly loaded plugin can define new classes. Package, it would seem like no. This reflection Java tutorial describes using reflection for accessing and manipulating classes, fields, methods, and constructors A constructor declaration includes the name, modifiers, parameters, and list of throwable exceptions. Check its docs for more interesting reflection methods. If X has getters and setters to its private fields, Y will have access to the private fields via those. Mar 31, 2019 · How to get Subclass object using implemented interface, if interface is used as Type Parameter for DynamoDBTypeConverter. How can I do this? Nov 20, 2009 · I am implementing a sort of ORM in Java. Additionally, we can instantiate new objects, invoke methods and get or set field values using reflection. class); for (Class<?> subTypeOfActionInPackageNameClass : allClasses) { Apr 23, 2013 · If you know what class the field is on you can access it using reflection. The source code Dec 27, 2013 · After their introduction in the JDK5, Java generics quickly became an integral element of many Java programs. getSubclasses to return [A,B]. If you do have a string representing the name of a class and you want to find that class's subclasses, then there are two steps: find the class given its name Is there a way to get a list of methods that would be accessible (not necessarily public) by a given class? The code in question will be in a completely different class. These are public, private, default, and protected. setAccessible as follows: Nov 30, 2015 · Suppose I use a single Java file which contains 2 classes like A & B (B extends A). Constructor class provides a way to obtain this information. getMethods(); The If class Y is a subclass (extends) class X, then class Y is also a class X, therefore having all the same fields except fields that are private to class X. On JVM you’d have to use Java API to scan all classes in all packages in all classpaths and then check if they’re a subclass. But in Apr 13, 2015 · If reflection is an option, you could first find all the classes of the dedicated package (Can you find all classes in a package using reflection?, How to get all classes names in a package?), then use: Jan 31, 2010 · C => B => A When executing, "C" calls one of "A"'s methods. You can just use the class directly, and you probably should. Note: This doesn't work for Java core internal classes. Is it possible to programmatically find a list of classes that have inherited MyClass? I know we can use reflection to discover all the superclasses of a given class Jun 1, 2024 · In Java, managing and discovering class hierarchies at runtime can be quite crucial, especially when dealing with large applications or frameworks. Explore the power of Java Reflection and dynamic class loading. ) How would I do this with Java reflection? And how can I future-proof it in case I add something between A & B or B & C? Jul 16, 2024 · Using Java Reflection you can inspect Java classes at runtime. Feb 2, 2017 · Java Reflections getSubTypeOf not returning all subclasses of the Hierarchy Asked 8 years, 9 months ago Modified 6 years, 10 months ago Viewed 3k times This reflection Java tutorial describes using reflection for accessing and manipulating classes, fields, methods, and constructors A constructor declaration includes the name, modifiers, parameters, and list of throwable exceptions. In this newsletter we show how to navigate the sealed class hierarchy and write a ClassSpliterator that can then create a Stream of classes. isPublic(field. getType(). That's kind of the whole point of subclasses. I know there is a getSuperclass method, but how do I access all the subclasses of it? EG, if A extends X and B extends X, then I want X. Example: public class A { In Java, obtaining a list of all classes that subclass a given parent class is not straightforward due to the lack of built-in reflection capabilities for this specific task. The Field class above is java. May 21, 2014 · Using Java Reflection you can inspect the methods of classes and invoke them at runtime. how do I get validation attributes for each property in main class and subclass which is a property itself. Nov 1, 2023 · Explore Java's Reflection API, its power in inspecting classes dynamically, and the intricacies of invoking methods & accessing fields at runtime. For Java, utilize reflection with `Class. __subclasses__ ()` method to retrieve subclasses directly. lang. We’ll write this program specifically for the JTextField class, but you should be able to easily adapt it to access class names in the inheritance hierarchy of any Java class. Learn how to use Java reflection to access fields of a subclass through its superclass. Let me get to the point: public class DB { public static Object find (int id) { Java Reflections getSubTypeOf not returning all subclasses of the Hierarchy I have the following code: Reflections reflections = new Reflections(packageName, new SubTypesScanner(false)); Set<Class<? extends Action>> allClasses = reflections. . All the subclasses have all the attributes and properties that have parent class. Discover how to list all Java subclasses with their fully qualified names efficiently using reflection and the ClassLoader. In C#, leverage the `Assembly` class to loop through types and check for inheritance. util. You may take a look at the whole java. You're given the name of the class in string format: So you do Class. Learn how to efficiently find all subclasses of a given class or implementors of an interface in Java using various techniques and best practices. The ConstructorSift example illustrates how to search a class's declared constructors for one which has a parameter of a given type. Nov 22, 2021 · Learn how to invoke public and private static methods using the Java Reflection API Nov 21, 2024 · Uncover the hidden power of Java reflection! Dive into its secrets, learn to navigate access control pitfalls, and master dynamic programming today! Nov 19, 2012 · You can use Class. ClassPathScanningCandidateComponentProvider can be used to find all subclass of a super class or an interface. Most Java programers are aware of the Java compiler’s type erasure. Solutions In Python, use the `. Jan 31, 2010 · Within that method in "A", I want to use reflection to find protected fields of the object that are defined in class "B". In this tutorial, we’ll explore several examples of how to find all classes in a Java package at runtime. java - methods There are two ways to access the methods of a class in Java: get () method Nov 6, 2012 · Let’s write a Java Reflection program to navigate through this class hierarchy and print out the class and package names. Alternatively, you can create two constructors, one for each subclass, that do the checks appropriate for that I've used Reflections Library to Find All Subclasses of a given class in Java before. However, when dealing with class hierarchies, developers may encounter situations where `getSubTypeOf` fails to return all subclasses, leading to confusion and potential bugs in the application. getGenericType() and Class. Usage: superClass. Aug 8, 2024 · Creating a Java object dynamically using reflection involves a few steps. We need toget subclass property validatation attributes also. Class. This example (it's in Groovy but the method calls are identical) gets a Field object for the class Foo and gets its value for the object b. And note: of course that only tells you about subclasses in that class path. By calling getSubClasses (MyClass. Now, if it is possible to retrieve all the attribute names and values of ChildObj, including the inherited attributes too, using Java reflection mechanism? Jun 27, 2017 · However we can no longer get all possible subclasses through Enum. For instance: public abstract class mainBaseClass{ May 24, 2007 · Class A{} say i have Class B extends A{} Class C extends A{} How do i get the number of subclasses of A during Runtime and also the "Class" objects???? Jul 23, 2025 · Class Name: The name of the class that must follow the rules as follows while creating the variables in java. The java. This particularly comes in handy when we don’t know their names at compile time. Implement a custom class loader that keeps track of subclass relationships as classes are loaded. How do you now get an instance of this? Apr 23, 2013 · If you know what class the field is on you can access it using reflection. equals(String. Contribute to ronmamo/reflections development by creating an account on GitHub. What I want? I want get some instance randomly but keep this part code in the subclass. e. For all its warts, Java's service loader is easy to understand and use. Learn how to utilize Java reflection to access subclass variable values and retrieve object instances from member fields effectively. getGenericSuperclass(). I need to access all the members of each subclass, but I need to isolate those members that exist in the base class from those that exists in subclasses. From the classes you can obtain information about Class Name Class Modifies (public, private, synchronized etc. Oct 5, 2010 · You mentioned "given its name". Since Python classes are first-class objects, you don't need to use a string with the class's name in place of the class or anything like that. Now let us discuss various scenarios of accessing protected members which are listed below as follows: Accessing in the same Mar 2, 2017 · Am trying to obtain and invoke a protected method residing in a different class and also different package using Java Reflection. Feb 26, 2019 · The simple answer is: yes, the only way to know about "accessible" subclasses of class X is to scan the complete class path for all classes, and for each one check whether it is a subclass of X. Jun 9, 2013 · As Jon had said earlier, type information is lost at runtime for generics. we can get super class fields as below: Jun 8, 2018 · How do I list down all the subclasses of a specific class or all the implementers of a specific interface in Java? Using Eclipse, I am able to do so but I want to know how to perform this programmatically? If you have any suggestions, please do put them. Discover best practices, common mistakes, and expert tips. Obtaining Method Objects The Method class is obtained from the Class object. The same is not true with non-generic code. May 11, 2024 · Polymorphic deserialization is a feature of Jackson, a popular JSON serialization and deserialization library for Java. Mar 19, 2024 · Getting Subclasses of a Sealed Class As we know, sealed classes and interfaces are inheritance hierarchies with a simple restriction: Only classes and interfaces in the same package can extend them. You have to interrogate the object (which is an instance of a sub-class) and ask if it is an: instanceof a particular sub-class, or call it's getClass() method. ) Package Info Superclass Implemented Interfaces Constructors Methods Fields Annotations plus a lot more information related to Java classes. Unfortunately there is no way to do this recursively. I would like to get a list of classes that implement an interface in Java at runtime so I can do a lookup service without having to hard code it. From Class#getDeclaredFields jadavoc (emphasis mine): Returns an array of Field objects reflecting all the fields declared by the class or interface represented by this Class object. Use a third-party library like Reflections or ClassGraph that can scan the classpath to find subclasses. It can then be discovered using the java. Jan 8, 2024 · A quick and practical guide to runtime method invocation using the Java Reflection API. Now I'm stuck with identifying the type of my fields. Introduction to Java Reflection for Classes The java. reflect have public constructors. forName (class_name). Super class : The parent class from which many subclasses can be created. May 17, 2013 · The base type contains all the members common to the subclasses. class Learn how to find all classes that implement a specific interface in Java using reflection and classpath scanning techniques. However, due to the dynamic nature of class loaders in Java, it is not straightforward to achieve this using reflection directly. Strings are easy, just do myField. See full list on docs. Jan 24, 2010 · Modifier. Is there a method that does this? I have a problem with a program in Java. In other words: there is always a restriction of scope. 2. My program have an interface Bonus and nine subclasses that extend Bonus. ReflectPermission, none of the classes in java. getModifiers()); The YourClassName. context. To get the idea of these modifiers, you can refer to access modifiers in java. Every Java Apr 16, 2025 · Methods A Method object let you get more information on the corresponding method: its type and its modifiers, the types and names of its parameters, and enables you to invoke it on a given object, passing the arguments you need. This capability can be particularly useful for Mar 10, 2022 · Reflection in Java to get class information. This guide will explain how to retrieve fields from both subclass and superclass using Java Reflection. getSubclasses ()` method. This includes public, protected, default (package) access, and private fields, but Apr 22, 2015 · The relationship between a class with protected fields and its subclasses is exactly the same as a class with public fields and unrelated classes. May 31, 2021 · Sometimes, we want to get information about the runtime behavior of our application, such as finding all classes available at runtime. I have to generate a random instance of Bonus and I can't use prototype pattern be Jun 17, 2015 · Is there a way to get/set private variables using reflection? (I've done it in C#, but this is the first time I've tried it in Java). This may not be a problem, depending on whether you control all the code that would need to be fixed in the event Jun 2, 2011 · Your question, "is it possible to find which subclass the superObject extends in Java?", is not making any sense. class), you can retrieve all subclasses of MyClass. Recently I had created a series of classes that each Retrieving Class Objects The entry point for all reflection operations is java. This is done via the Java class java. This guide provides detailed explanations, code examples, and common mistakes. ServiceLoader class which, when given a Class object, will generate instances of all the declared subclasses of that class (or, if the Class represents an interface, all the classes implementing that interface). It is important to note that due to the method’s use of reflection, there may be performance issues, especially when dealing with a large number of classes. It shows that you don't have to care about the exact concrete class of the object, what matters is that you know the class the field is on and that that class is either the concrete Aug 4, 2010 · By the way, GenericTypeResolver will still get null for the non-subclasses class like the question mentioned, because the generic info of such class was completely erased after compilation. With the exception of java. springframework. class); for (Class<?> subTypeOfActionInPackageNameClass : allClasses) { Java has two camps, 1) How do I hide everything and make 3 lines of code 3000, and 2) This idiot hid everything, how do I use reflection to get at it again and keep my life simple =) I need to get an array of subclasses of class X. This is a code snippet that I use in a simple java project : Reflections reflections = new Reflections( Jul 23, 2025 · In Java, there are four types of access modifiers. annotation. Use a class literal of the NameOfTheActualClass. It shows that you don't have to care about the exact concrete class of the object, what matters is that you know the class the field is on and that that class is either the concrete Learn how to access superclass fields using Java reflection. Jun 25, 2009 · 171 I've a Java object 'ChildObj' which is extended from 'ParentObj'. I got to know that we can use reflection how to do it? This is my POJO Class which will extend my reflection class.