![]() The ClassMethodTest class below illustrates this. If you'd like to list the public, protected, and private methods that the class declares, you can do so by calling the getDeclaredMethods() method of the class object, which returns an array of Method objects representing the methods that are declared by the class. import you have an object, you can get its Class object by calling getClass() on the object. Another example would be an application that analyzes the content of given classes and executes the methods that contain a specific annotation with arguments. It takes any object as a parameter and uses the Java reflection API to print out every field name and value. One of my favorite uses of reflection is the below Java dump method. Most other modern languages use reflection as well, and in scripting languages (such as Python) they are even more tightly integrated, since it feels more natural within the general programming model of those languages. For example, all objects in Java have the method getClass (), which lets you determine the objects class even if you dont know it at compile time (e.g. Lots of modern frameworks use reflection extensively for this very reason. The code can be written against known interfaces, but the actual classes to be used can be instantiated using reflection from configuration files. Reflection is important since it lets you write programs that do not have to "know" everything at compile time, making them more dynamic, since they can be tied together at runtime. More advanced uses lets you list and call methods, constructors, etc. This month I'll take a look at the Java Reflection API. if you declared it as an Object) - this might seem trivial, but such reflection is not possible in less dynamic languages such as C++. That example is a form of static introspection. ![]() at runtime.įor example, all objects in Java have the method getClass(), which lets you determine the object's class even if you don't know it at compile time (e.g. ![]() Example 1 Get the Class class object and calling their methods using java reflection. Reflection is a language's ability to inspect and dynamically call classes, methods, attributes, etc. Class class example using reflection in java. Support introspection, but do not support reflection. public Method getDeclaredMethod(String name,Class parameterTypes), This method returns the method class. The distinction is necessary here as some languages It returns the total number of methods of the class. Reflection is then theĪbility to make modifications at runtime by making use of Not reflection, but rather Type Introspection. The ability to inspect the code in the system and see object types is In dynamically typed languages, the use case described above is less necessary (since the compiler will allow any method to be called on any object, failing at runtime if it does not exist), but the second case of looking for methods which are marked or work in a certain way is still common. There are some good reflection examples to get you started at Īnd finally, yes, the concepts are pretty much similar in other statically typed languages which support reflection (like C#). JUnit 4, for example, will use reflection to look through your classes for methods tagged with the annotation, and will then call them when running the unit test. One very common use case in Java is the usage with annotations. The following example shows the usage of () method. So, to give you a code example of this in Java (imagine the object in question is foo) : Method method = foo.getClass().getMethod("doSomething", null) Java's static typing system isn't really designed to support this unless the object conforms to a known interface, but using reflection, your code can look at the object and find out if it has a method called 'doSomething' and then call it if you want to. The name reflection is used to describe code which is able to inspect other code in the same system (or itself).įor example, say you have an object of an unknown type in Java, and you would like to call a 'doSomething' method on it if one exists.
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