反射调用成员属性

成员属性保存了一个对象的所有信息，通过反射可以实现成员属性的赋值与取值操作，本课程主要讲解了属性的直接操作，以及封装性取消等操作。

1.获取类中的成员属性信息

package com.youtube.demo;

import java.lang.reflect.Field;;

interface IChannelService{
    public static final String NAME = "youtube";
}
abstract class AbsBase{
    protected static final String BASE = "www.youtube.com";
    private String info = "Hello, youtube";
}
class Member extends AbsBase implements IChannelService{
    private String name;
    private int age;
}
public class JavaReflectDemo {
    public static void main(String[] args) {
        Class <?> cls = Member.class;
        {
            Field fields[] = cls.getFields();
            for(Field field:fields) {
                System.out.println(field);
            }
        }
        System.out.println("----------------华丽的分割线------------------");
        {
            Field fields[] = cls.getDeclaredFields();
            for(Field field:fields) {
                System.out.println(field);
            }
        }
    }
}

运行结果：

public static final java.lang.String com.youtube.demo.IChannelService.NAME
----------------华丽的分割线------------------
private java.lang.String com.youtube.demo.Member.name
private int com.youtube.demo.Member.age

2.反射操作成员属性内容：

package com.facebook.demo;
import java.lang.reflect.Field;
class Member{
    private String name;
}
public class JavaReflectDemo {
    public static void main(String[] args) throws Exception {
        Class<?> cls = Member.class;
        Object obj = cls.getDeclaredConstructor().newInstance();
        Field nameField = cls.getDeclaredField("name");
        nameField.setAccessible(true);//解除封装
        nameField.set(obj, "小李老师");
        System.out.println(nameField.get(obj));
    }
}

运行结果：

小李老师

如果不解除封装，会抛如下异常：

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.获取指定属性类型：

package com.facebook.demo;
import java.lang.reflect.Field;
class Member{
    private String name;
}
public class JavaReflectDemo {
    public static void main(String[] args) throws Exception {
        Class<?> cls = Member.class;
        Object obj = cls.getDeclaredConstructor().newInstance();
        Field nameField = cls.getDeclaredField("name");
        System.out.println(nameField.getType().getName());
        System.out.println(nameField.getType().getSimpleName());
    }
}

运行结果：

java.lang.String
String