A Class object is also provided to represent the void return type. Table A: Class objects for primitive typesĪlthough primitive types are not classes, Java provides correspondent Class objects so that it is possible to represent primitive types in parameter lists, field types, and methods return types. Although primitive types are not classes, Java provides correspondent Class objects to represent them, as shown in Table A. You can get the definition of a constructor by calling the method Class.getConstructor(Class), passing an array of Class objects that represent the parameter types of the desired constructor. However, the Reflection API allows you to select which constructor to call.įirst, you must get the definition of the constructor you want, which is represented by an instance of the class. you can create new instances of classes, much like the Class method newInstance(). If you have an instance of the class, you can also call its getClass() method. One way is to call the static method forName(String) of Class, specifying the fully qualified name of the class you want. So you must first get the Class object that represents the class you are interested in. The only way to get access to the class definition is through appropriate methods of Class. You can also manipulate the fields or call constructors and methods, subject to the language and Java Virtual Machine (JVM) access restrictions. Each class provides a suitable API that lets you get any information about the entity it represents, such as the name and type of a field and the parameters of a constructor or method. These are returned as instances of the classes in the package. Invoking such methods on a Class object, you can get the complete definition of the class it represents, such as its constructors, methods, and fields. The Java Reflection API is composed of the classes in the package and methods of. For example, you can use the Reflection API to inspect objects, browse classes, and create callback methods, such as event handlers, without extending a specific class or implementing an interface. That allows the easy creation of applications that wouldn’t otherwise be possible. This walk-through will show you how to access class definitions at runtime.Īvailable since Java 1.1, the Reflection API allows a Java application to get the definition of classes and operate on them at runtime without having them available at compile time. The Java Reflection API is a long-standing tool that opens the door to a variety of programming techniques. Java Reflection API helps leverage the power of classes
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