This immutable Class object is fundamentally different from instances of a class. Every unique Object is assigned an immutable Class object by the JVM. From the Java Class API, we see that Class is a subclass of Object. Create new instance of existing objects, invoke methods and change values of fields of existing objects.īefore getting started with reflections in Java, it is important to realize that a class is also an object.This is very useful if you are interested to implement test cases for private methods. Access private fields and methods of a class without having to modify the visibility modifier of the class itself.In particular, reflections in Java allows the inspection of classes, methods and fields during runtime, without having any knowledge of it during compile time. The reflection library provides a Type interface to describe a generic type.Reflection is the ability of a computer program to examine, inspect and modify its own behaviour at runtime. In the meantime, all the necessary information is available, and we explain how to access it in the Sun is considering adding such a method in future. Unfortunately, there is no toGenericString method for the class Class, even though It is preserved only for use in reflection. The informationĪbout generic types is essentially a comment. Tokens contains no information about generic types, the actual bytecode of the classĭoes encode information about generic types as well as erased types. The sample run shows that although the reified type information for objects and class Public static Class getComponentType(T a) Object newobj = obj.getClass().getConstructor().newInstance() A type-safe library for generic reflection However, in each case the unchecked cast is safe, and users canĬall on the four library routines defined here without violating the cast-iron guarantee.Įxample 7-1. Type Class, because of the erasure that is required to ensure that class tokens always The method getClass, whenĬalled on a receiver of type T, returns a token not of type Class but of T, because it may return an array of a primitive type. must have the return type Object rather than the return type Receiver is not a class token for an array type). Is in the class Class, and Java provides no way to restrict the receiver type to beĬlass in the signature of the method (though the call raises an exception if the Return sufficiently accurate types, for various reasons. Unchecked casts are required because the methods in the Java reflection library cannot Reflection library and an unchecked cast to the appropriate return type. The code for each of theįirst three methods consists of a call to one or two corresponding methods in the Java Size it simply composes calls to the previous two methods. The fourth takes an array and a size, andĪllocates a new array with the same component type as the given array and the given Conversely, the third allocates a new array with its component type specifiedīy a given class token and a specified size. The second takes an arrayĪnd returns a class token for its component type, as carried in its run-time type information. The class this must have the same type as the original object. The first takes an object, finds the class of that object, and returns a new instance of It defines a convenience class GenericReflection containing the following methods: Sun is considering adding library methods similar to the ones described here.Įxample 7-1 provides a library of generic functions that use reflection in a type-safe
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