JavaSE-24.2.3反射获取成员变量并使用

Posted 2021-06-20 yub4by

 1 package day15.lesson2;
 2 
 3 import java.lang.reflect.Constructor;
 4 import java.lang.reflect.Field;
 5 import java.lang.reflect.InvocationTargetException;
 6 
 7 /*
 8 2.6 反射获取成员变量并使用
 9 
10     Class类获取成员变量对象的方法
11         Field[] getFields() 返回所有公共成员变量对象的数组
12         Field[] getDeclaredFields() 返回所有成员变量对象的数组
13         Field getField(String name) 返回单个公共成员变量对象
14         Field getDeclaredField(String name) 返回单个成员变量对象
15 
16     Field类用于给成员变量赋值的方法
17         void set(Object obj,Object value) 给obj对象的成员变量赋值为value
18 
19  */
20 public class Demo4Reflect {
21     public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
22         Class<?> c = Class.forName("day15.lesson2.Student");
23 
24         Field[] fields = c.getFields();
25         for (Field f: fields){
26             System.out.println(f);
27         }
28         //public java.lang.String day15.lesson2.Student.address
29         System.out.println();
30 
31         Field[] declaredFields = c.getDeclaredFields();
32         for (Field f: declaredFields){
33             System.out.println(f);
34         }
35         /*
36         private java.lang.String day15.lesson2.Student.name
37         int day15.lesson2.Student.age
38         public java.lang.String day15.lesson2.Student.address
39          */
40         System.out.println();
41 
42         Field addressField = c.getField("address"); //公共的成员变量
43         /*Student s = new Student();
44         s.address = "南京";
45         System.out.println(s);*/
46         //通过反射实现上述功能
47         Constructor<?> con = c.getConstructor(); //获取公共无参构造
48         Object obj = con.newInstance(); //创建对象
49         addressField.set(obj, "南京"); //给对象obj的成员变量addressField赋值"南京"
50         System.out.println(obj); //Student{name=\'null\', age=0, address=\'南京\'}
51         System.out.println();
52 
53 //        Field declaredField = c.getDeclaredField("name"); //私有成员变量
54     }
55 }

 1 class Student{
 2     //成员变量
 3     private String name; //私有
 4     int age; //默认
 5     public String address; //公共
 6 
 7     //构造方法
 8     public Student() { //公共
 9     }
10 
11     public Student(String name, int age, String address) { //公共
12         this.name = name;
13         this.age = age;
14         this.address = address;
15     }
16 
17     private Student(String name){ //私有
18         this.name = name;
19     }
20 
21     Student(String name, int age){ //默认
22         this.name = name;
23         this.age = age;
24     }
25 
26     //成员方法
27     private void function(){ //私有
28         System.out.println("function");
29     }
30 
31     public void method1(){ //公共
32         System.out.println("method");
33     }
34 
35     public void method2(String s){ //公共
36         System.out.println("method:" + s);
37     }
38 
39     public String method3(String s, int i){ //公共
40         return s + "," + i;
41     }
42 
43     @Override
44     public String toString() { //公共
45         return "Student{" +
46                 "name=\'" + name + \'\\\'\' +
47                 ", age=" + age +
48                 ", address=\'" + address + \'\\\'\' +
49                 \'}\';
50     }
51 }

 1 package day15.lesson2;
 2 
 3 import java.lang.reflect.Constructor;
 4 import java.lang.reflect.Field;
 5 import java.lang.reflect.InvocationTargetException;
 6 
 7 /*
 8 2.7 反射获取成员变量并使用练习
 9 
10     通过反射获取成员变量并赋值
11 
12     通过反射实现一下操作：
13         Student s = new Studet();
14         s.name = "tom";
15         s.age = 23;
16         s.address = "南京";
17         sout(s);
18  */
19 public class Demo5Reflect {
20     public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchFieldException {
21         Class<?> c = Class.forName("day15.lesson2.Student");
22 
23 //        Student s = new Student();
24         Constructor<?> con = c.getConstructor();
25         Object obj = con.newInstance();
26         System.out.println(obj); //Student{name=\'null\', age=0, address=\'null\'}
27 
28 //        s.name = "tom";
29         Field nameField = c.getDeclaredField("name"); //私有只能用xxxDeclaredxxx
30         nameField.setAccessible(true); //私有得暴力反射
31         nameField.set(obj, "tom");
32         System.out.println(obj); //Student{name=\'tom\', age=0, address=\'null\'}
33 
34 //        s.age = 23;
35         Field ageField = c.getDeclaredField("age"); //默认的也只能用xxxDeclaredxxx
36         ageField.set(obj, 23);
37         System.out.println(obj); //Student{name=\'tom\', age=23, address=\'null\'}
38 
39 //        s.address = "南京";
40 //        Field addressField = c.getField("address"); //公共的既能用getField也能用getDeclaredField
41         Field addressField = c.getDeclaredField("address"); //为了方便统一用getDeclaredField即可
42         addressField.set(obj, "南京");
43         System.out.println(obj); //Student{name=\'tom\', age=23, address=\'南京\'}
44     }
45 }