反射調用成員屬性

成員屬性保存了一個對象的所有信息，通過反射可以實現成員屬性的賦值與取值操作，本課程主要講解了屬性的直接操作，以及封裝性取消等操作。

1.獲取類中的成員屬性信息

 1 package com.youtube.demo;
 2 
 3 import java.lang.reflect.Field;;
 4 
 5 interface IChannelService{
 6     public static final String NAME = "youtube";
 7 }
 8 abstract class AbsBase{
 9     protected static final String BASE = "www.youtube.com";
10     private String info = "Hello, youtube";
11 }
12 class Member extends AbsBase implements IChannelService{
13     private String name;
14     private int age;
15 }
16 public class JavaReflectDemo {
17     public static void main(String[] args) {
18         Class <?> cls = Member.class;
19         {
20             Field fields[] = cls.getFields();
21             for(Field field:fields) {
22                 System.out.println(field);
23             }
24         }
25         System.out.println("----------------華麗的分割線------------------");
26         {
27             Field fields[] = cls.getDeclaredFields();
28             for(Field field:fields) {
29                 System.out.println(field);
30             }
31         }
32     }
33 }

運行結果：

public static final java.lang.String com.youtube.demo.IChannelService.NAME
----------------華麗的分割線------------------
private java.lang.String com.youtube.demo.Member.name
private int com.youtube.demo.Member.age

2.反射操作成員屬性內容：

 1 package com.facebook.demo;
 2 import java.lang.reflect.Field;
 3 class Member{
 4     private String name;
 5 }
 6 public class JavaReflectDemo {
 7     public static void main(String[] args) throws Exception {
 8         Class<?> cls = Member.class;
 9         Object obj = cls.getDeclaredConstructor().newInstance();
10         Field nameField = cls.getDeclaredField("name");
11         nameField.setAccessible(true);//解除封裝
12         nameField.set(obj, "小李老師");
13         System.out.println(nameField.get(obj));
14     }
15 }

運行結果：

小李老師

如果不解除封裝，會拋如下異常：

Exception in thread "main" java.lang.IllegalAccessException: class com.facebook.demo.JavaReflectDemo cannot access a member of class com.facebook.demo.Member with modifiers "private"
    at java.base/jdk.internal.reflect.Reflection.newIllegalAccessException(Reflection.java:355)
    at java.base/java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:639)
    at java.base/java.lang.reflect.Field.checkAccess(Field.java:1075)
    at java.base/java.lang.reflect.Field.set(Field.java:778)
    at com.facebook.demo.JavaReflectDemo.main(JavaReflectDemo.java:11)

3.獲取指定屬性類型：

 1 package com.facebook.demo;
 2 import java.lang.reflect.Field;
 3 class Member{
 4     private String name;
 5 }
 6 public class JavaReflectDemo {
 7     public static void main(String[] args) throws Exception {
 8         Class<?> cls = Member.class;
 9         Object obj = cls.getDeclaredConstructor().newInstance();
10         Field nameField = cls.getDeclaredField("name");
11         System.out.println(nameField.getType().getName());
12         System.out.println(nameField.getType().getSimpleName());
13     }
14 }

運行結果：

java.lang.String
String