1. 定义

JAVA反射（放射）机制：“程序运行时，允许改变程序结构或变量类型，这种语言称为动态语言”。从这个观点看，Perl，Python，Ruby是动态语言，C++，Java，C#不是动态

语言。但是JAVA有着一个非常突出的动态相关机制：Reflection，用在Java身上指的是我们可以于运行时加载、探知、使用编译期间完全未知的classes。换句话说，Java程序

可以加载一个运行时才得知名称的class，获悉其完整构造（但不包括methods定义），并生成其对象实体、或对其fields设值、或唤起其methods。其中，有一个Class类型，

它是实现反射的起源，针对任何您想探勘的类，唯有先为它产生一个Class 对象，接下来才能经由后者唤起为数十多个的Reflection APIs。而关于jvm如何加载类的过程，见文

章： 。

2. 实例应用

案例接口

public interface China {	public void sayHello(String name, Integer age);}

案例类

public class Person implements China{	private int age;		private String name;	public int getAge() {		return age;	}	public final void setAge(Integer age) {		this.age = age;	}	public String getName() {		return name;	}	public void setName(String name) {		this.name = name;	}	@Override	public String toString() {		return "Person [age=" + age + ", name=" + name + "]";	}	public Person(int age, String name) {		super();		this.age = age;		this.name = name;	}		public Person(int age){		super();		this.age = age;	}		public Person(String name){		super();		this.name = name;	}	public Person() {		super();	}	@Override	public void sayHello(String name, Integer age) {		System.out.println("hello "+ name + " : " + age);	}}

测试类

public class ReflectTest {	/**	 * 通过Class.forName和ClassLoader来加载类	 * @throws ClassNotFoundException	 */	@Test	public void test1() throws ClassNotFoundException{		Class
      demo1 = null;		Class
      demo2 = null;		Class
      demo3 = null;		Class
      demo4 = null;		demo1 = Class.forName("cn.test.reflect.Demo");		demo2 = new Demo().getClass();		demo3 = Demo.class;		demo4 = Demo.class.getClassLoader().loadClass("cn.test.reflect.Demo");		System.out.println(demo1.getName());		System.out.println(demo2.getName());		System.out.println(demo3.getName());		System.out.println(demo4.getName());	}		/**	 * 通过Class.forName("").newInstance()生成新对象，调用的是无参构造函数	 * @throws ClassNotFoundException	 * @throws InstantiationException	 * @throws IllegalAccessException	 */	@Test	public void test2() throws ClassNotFoundException, InstantiationException, IllegalAccessException{		Class
      demo = Class.forName("cn.test.reflect.Person");		Person person = (Person) demo.newInstance();		person.setAge(12);		person.setName("张三");		System.out.println(person);	}	/**	 * 打印出该类所有的信息：属性，方法，构造函数	 * @throws ClassNotFoundException	 */	@Test	public void test3() throws ClassNotFoundException{		Class
      demo = Class.forName("cn.test.reflect.Person");		System.out.println("类属性");		Field[] fields = demo.getDeclaredFields();		for(Field field : fields){			int mo = field.getModifiers();			System.out.print(Modifier.toString(mo)+" ");			System.out.print(field.getType().getName()+" ");			System.out.print(field.getName());			System.out.println();		}		System.out.println("所有方法");		Method[] methods = demo.getDeclaredMethods();		for(Method method : methods){			Class
     [] parms = method.getParameterTypes();			int mo = method.getModifiers();			System.out.print(Modifier.toString(mo)+" ");			System.out.print(method.getName()+"(");			int i=1;			for(Class
      parm : parms){				System.out.print(parm.getName() + " arg"+i++);				if(i<=parms.length){					System.out.print(",");				}			}			System.out.print(")");			System.out.println();		}				Constructor
     [] constructors = demo.getConstructors();		System.out.print("构造方法：");		for(Constructor
      constructor : constructors){			System.out.println();			Class
     [] parms = constructor.getParameterTypes();			int mo = constructor.getModifiers();			System.out.print(Modifier.toString(mo)+" ");			System.out.print(constructor.getName()+"(");			int i=1;			for(Class
      parm : parms){				System.out.print(parm.getName() + " arg"+i++);				if(i<=parms.length){					System.out.print(",");				}			}			System.out.print("){}");		}	}		/**	 * 获取接口	 * @throws ClassNotFoundException 	 */	@Test	public void test4() throws ClassNotFoundException{		Class
      demo = Class.forName("cn.test.reflect.Person");		Class
     [] intes = demo.getInterfaces();		for(Class
      interf : intes){			System.out.println(interf.getName());		}	}		/**	 * 获取父类	 * @throws ClassNotFoundException	 */	@Test	public void test5() throws ClassNotFoundException{		Class
      demo = Class.forName("cn.test.reflect.Person");		Class
      superClass = demo.getSuperclass();		System.out.println(superClass.getName());	}		/**	 * 反射调用类的中任意方法，需要知道方法名	 * @throws ClassNotFoundException 	 * @throws IllegalAccessException 	 * @throws InstantiationException 	 * @throws SecurityException 	 * @throws NoSuchMethodException 	 * @throws InvocationTargetException 	 * @throws IllegalArgumentException 	 */	@Test	public void test6() throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException{		Class
      demo = Class.forName("cn.test.reflect.Person");		Person person = (Person) demo.newInstance();		Method sayHelloMethod = demo.getMethod("sayHello", String.class, Integer.class);		sayHelloMethod.invoke(person, "张三", 20);				Method setAgeMethod = demo.getMethod("setAge", Integer.class);		setAgeMethod.invoke(person, 2);				Method getAgeMethod = demo.getMethod("getAge");		System.out.println(getAgeMethod.invoke(person));				Method setNameMethod = demo.getMethod("setName", String.class);		setNameMethod.invoke(person, "李四");				Method getNameMethod = demo.getMethod("getName");		System.out.println(getNameMethod.invoke(person));				Method toStringMethod = demo.getMethod("toString");		System.out.println(toStringMethod.invoke(person));	}	/**	 * 反射设置属性值	 * @throws ClassNotFoundException	 * @throws InstantiationException	 * @throws IllegalAccessException	 * @throws NoSuchMethodException	 * @throws SecurityException	 * @throws IllegalArgumentException	 * @throws InvocationTargetException	 * @throws NoSuchFieldException 	 */	@Test	public void test7() throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException, NoSuchFieldException{		Class
      demo = Class.forName("cn.test.reflect.Person");		Person person = (Person) demo.newInstance();				Field ageField = demo.getDeclaredField("age");		ageField.setAccessible(true);		ageField.set(person, 10);				Field nameField = demo.getDeclaredField("name");		nameField.setAccessible(true);		nameField.set(person, "王武");				System.out.println(person);	}}