Java Reflection feature One

Tag: ADC size reflection for memory pre. Class generic Generation

A. Class understanding

        /         * * Class is the source of reflection         * Create a class, compile (Javac.exe), generate the corresponding. class file, and then use Java.exe to load (completed by the JVM's ClassLoader) this. class file.         * When this. class file is loaded into memory, it is a runtime class that is stored in the cache.         * then this runtime class is itself an instance of class.         * 1. Each runtime class is loaded only once;         * 2. Once you have an instance of class, you can do the following:         *    1> Create objects of the corresponding runtime class         *    2> Gets the complete structure of the corresponding run class (properties, methods, constructors, inner classes, parent classes, packages, exceptions, annotations 、...         *    3> calls the corresponding runtime class for the specified structure (properties, methods, constructors)         *    4> Reflection application: Dynamic Agent         */

A method of acquiring a class object

1) obtained by class's Static property class

Class clazz = Person.class;

2) obtained by the GetClass method of the runtime class

        person person = new person ();        Class clazz = Person.getclass ();    

3) obtained by the static method of class

        String className = "Hello." Person ";//The fully qualified name of the run-time class, class        Clazz = Class.forName (className);

4) obtained through the class loader (learn)

        String className = "Hello." Person ";//The fully qualified name of the class        ClassLoader ClassLoader = This.getclass (). getClassLoader ();        Class clazz = Classloader.loadclass (className);

　　

Second, create an instance object of the corresponding run-time class through the class object

        Class Clazz = person.class;//does not use generics, default is the class object of object type person person        = (person) clazz.newinstance ();  A strong turn is required, and the method defaults to calling the run-time class's parameterless construction method, so the class must have no parameter construction method, the permission is large enough        class<person> clazz1 = person.class;// A generic is used that specifies the class object of the person type person        Person1 = clazz1.newinstance ();//does not require a strong turn

Java Reflection feature One