Java 反射

Posted 2021-03-02 benniaoxianfei

反射（Reflection）: 在多个类没有公共特性时，

                    可以在一个基类方法中，

                    通过反射，

                    实现对这些没有公共特性的类的普遍性调用。

 

一：class.getMethod()

　　①//getMethod(String name, Class<?>... parameterTypes)

 　　      Method method = class.getMethod("要调用的方法名称","要调用的方法的形参的类型的class");

    ②//invoke(Object obj, Object... args)

　　  method.invoke("对象实例","要调用的方法的形参");

 1 public class ReflectiveTest {
 2 
 3     public static void reflectiveMethod(Object object) {
 4 
 5         System.out.println("-------------反射使用方法--------------");
 6 
 7         Class<?> clazz = object.getClass();
 8         try {
 9 
10             //getMethod():第一个参数方法名称；第二个参数：方法的形参的class
11             Method sitMethod = clazz.getMethod("sit",null);
12             sitMethod.invoke(object,null);
13         } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
14             e.printStackTrace();
15         }
16 
17 
18         try {
19             Method eatMethod = clazz.getMethod("eat",String.class);
20             eatMethod.invoke(object,"pork");
21         } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
22             e.printStackTrace();
23         }
24 
25         try {
26 
27             Method calculateMethod = clazz.getMethod("calculate",int.class,int.class);
28             int a = (Integer) calculateMethod.invoke(object,1024,2048);
29             System.out.println("calculateMethod 结果=" + a);
30         } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
31             e.printStackTrace();
32         }
33 
34     }
35 
36 
37     public static void main(String[] args) {
38 
39         Dog dog = new Dog();
40         Robot robot = new Robot();
41 
42         reflectiveMethod(dog);
43         reflectiveMethod(robot);
44     }
45 
46 
47 }

运行结果：

 1 -----------------反射使用方法-------------------
 2 Dog sits 
 3 Dog eats pork
 4 java.lang.NoSuchMethodException: com.wing.test.vo.Dog.calculate(int, int)
 5     at java.lang.Class.getMethod(Class.java:1786)
 6     at com.wing.test.ReflectiveTest.reflectiveMethod(ReflectiveTest.java:41)
 7     at com.wing.test.ReflectiveTest.main(ReflectiveTest.java:56)
 8 java.lang.NoSuchMethodException: com.wing.test.vo.Robot.eat(java.lang.String)
 9     at java.lang.Class.getMethod(Class.java:1786)
10     at com.wing.test.ReflectiveTest.reflectiveMethod(ReflectiveTest.java:33)
11     at com.wing.test.ReflectiveTest.main(ReflectiveTest.java:57)
12 -----------------反射使用方法-------------------
13 Robot sits
14 Robot calculates a + b = 3072
15 calculateMethod 结果=3072

 

辅助类：

 1 public class Dog {
 2 
 3     public Dog() {
 4     }
 5 
 6     public void sit(){
 7         System.out.println("Dog sits ");
 8     }
 9 
10     public void eat(String meat){
11         System.out.println("Dog eats " + meat);
12     }
13 
14 
15 }
16 
17 
18 public class Robot {
19 
20     public Robot() {
21     }
22 
23     public void sit(){
24         System.out.println("Robot sits");
25     }
26 
27     public int calculate(int a,int b){
28         int c = a + b;
29         System.out.println("Robot calculates a + b = " + c);
30         return c;
31     }
32 
33 }