Java反射

什么是反射？
即通过字节码文件对象去使用成员。

(1)获取字节码文件对象的三种方式：    A:Object类的getClass()方法    B:数据类型的静态class属性    C:Class类的静态方法forName()

得到字节码文件对象后，我们可以通过这个对象获取类的构造方法，并创建对象，使用它的成员方法和成员变量。

举例：构造方法的遍历和调用

public class ConstructorTest {    /**     * @param args     * @throws ClassNotFoundException      * @throws SecurityException      * @throws NoSuchMethodException      * @throws InvocationTargetException      * @throws IllegalArgumentException      * @throws IllegalAccessException      * @throws InstantiationException      */    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {        // TODO Auto-generated method stub        Class<?> a = Class.forName("com.day17.constructor.Animal");        Constructor<?>[] con = a.getConstructors();    //获取公开的构造方法        for (Constructor<?> co : con) {            System.out.println(co);   //public com.day17.constructor.Animal()        }        System.out.println("-------------");        Constructor<?>[] con2 = a.getDeclaredConstructors();    //获取所有的构造方法        for (Constructor<?> co : con2) {            System.out.println(co);        //com.day17.constructor.Animal(java.lang.String,int,java.lang.String)                                           //public com.day17.constructor.Animal()        }        System.out.println("-------------");        Constructor<Animal> dcon = (Constructor<Animal>) a.getDeclaredConstructor(String.class,int.class,String.class);        dcon.setAccessible(true);        Animal ni = dcon.newInstance("小狗",20,"白色");        System.out.println(ni);    }}

举例：成员方法的遍历和调用（成员变量同理）

public class MethodTest {    /**     * @param args     * @throws ClassNotFoundException      * @throws Exception      * @throws NoSuchMethodException      */    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, Exception {        // TODO Auto-generated method stub        Class<?> c = Class.forName("com.day17.method.Animal");        Constructor<?> con = c.getConstructor();        Object ni = con.newInstance();        Method[] dm = c.getDeclaredMethods();        for (Method method : dm) {            System.out.println(method);        }        System.out.println("-----------------");        Method dme = c.getDeclaredMethod("eat");        System.out.println(dme);        dme.invoke(ni);        Method dmf = c.getDeclaredMethod("fun");        dmf.setAccessible(true);        dmf.invoke(ni);    }}