Java-反射2020年

短命女 2022-12-28 00:59 145阅读 0赞

### 文章目录 ###

*  一、反射概述
 *  二、获取Class类对象的三种方式
 *  三、反射获取构造方法
 *   *  1.Class类获取构造方法对象的方法
     *  2.Constructor类创建对象的方法
 *  四、反射获取成员变量
 *   *  1.Class类获取成员变量对象的方法
     *  2.Field类用于给成员变量赋值的方法
 *  四、反射获取成员方法
 *   *  1.Class类获取成员方法对象的方法
     *  2.Method类用于执行方法的方法

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# 一、反射概述 #

反射机制是在运行状态中，对于任意一个类，都能够知道这个类的所有属性和方法；对于任意一个对象，都能够调用它的任意属性和方法；这种动态获取信息以及动态调用对象方法的功能称为Java语言的反射机制。

# 二、获取Class类对象的三种方式 #

*  类名.class属性
 *  对象名.getClass()方法
 *  Class.forName(全类名)方法

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NjAwNjk4OA_size_16_color_FFFFFF_t_70]

# 三、反射获取构造方法 #

## 1.Class类获取构造方法对象的方法 ##

<table> 
 <thead> 
  <tr> 
   <th>方法名</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Constructor&lt;?&gt;[] getConstructors()</td> 
   <td>返回所有公共构造方法对象的数组</td> 
  </tr> 
  <tr> 
   <td>Constructor&lt;?&gt;[] getDeclaredConstructors()</td> 
   <td>返回所有构造方法对象的数组</td> 
  </tr> 
  <tr> 
   <td>Constructor&lt;T&gt; getConstructor(Class&lt;?&gt;… parameterTypes)</td> 
   <td>返回单个公共构造方法对象</td> 
  </tr> 
  <tr> 
   <td>Constructor&lt;T&gt; getDeclaredConstructor(Class&lt;?&gt;… parameterTypes)</td> 
   <td>返回单个构造方法对象</td> 
  </tr> 
 </tbody> 
</table>

## 2.Constructor类创建对象的方法 ##

<table> 
 <thead> 
  <tr> 
   <th>方法名</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>T newInstance(Object…initargs)</td> 
   <td>根据指定的构造方法创建对象</td> 
  </tr> 
  <tr> 
   <td>setAccessible(boolean flag)</td> 
   <td>设置为true,表示取消访问检查</td> 
  </tr> 
 </tbody> 
</table>

Student类

public class Student {
        
        private String name;
        private int age;
    
        private Student(String name) {
        
            System.out.println("name的值为:" + name);
            System.out.println("private...Student...有参构造方法");
        }
    
        public Student() {
        
            System.out.println("public...Student...无参构造方法");
        }
    
        public Student(String name, int age) {
        
            System.out.println("name的值为:" + name + "age的值为:" + age);
            System.out.println("public...Student...有参构造方法");
        }
    }

测试类ReflectDemo1

import java.lang.reflect.Constructor;
    import java.lang.reflect.InvocationTargetException;
    
    public class ReflectDemo1 {
        
        public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
        
            method1();
            method2();
            method3();
            method4();
    
        }
    
        private static void method4() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {
        
            Class clazz = Class.forName("csdn.csdn3.Student");
            Constructor constructor = clazz.getDeclaredConstructor(String.class);
            constructor.setAccessible(true);
            Student student = (Student) constructor.newInstance("zhangsan");
            System.out.println(student);
        }
    
        private static void method3() throws ClassNotFoundException, InstantiationException, IllegalAccessException {
        
            Class clazz = Class.forName("csdn.csdn3.Student");
            Student student = (Student) clazz.newInstance();
            System.out.println(student);
        }
    
        private static void method2() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {
        
            Class clazz = Class.forName("csdn.csdn3.Student");
            Constructor constructor = clazz.getConstructor();
            Student student = (Student) constructor.newInstance();
            System.out.println(student);
        }
    
        private static void method1() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {
        
            Class clazz = Class.forName("csdn.csdn3.Student");
            Constructor constructor = clazz.getConstructor(String.class, int.class);
            Student student = (Student) constructor.newInstance("zhangsan", 23);
            System.out.println(student);
        }
    }

> name的值为:zhangsanage的值为:23  
> public…Student…有参构造方法  
> csdn.csdn3.Student@7cd84586  
> public…Student…无参构造方法  
> csdn.csdn3.Student@30dae81  
> public…Student…无参构造方法  
> csdn.csdn3.Student@1b2c6ec2  
> name的值为:zhangsan  
> private…Student…有参构造方法  
> csdn.csdn3.Student@79fc0f2f

注意：

*  如果是public的，直接创建对象  
    newInstance(Object… initargs)
 *  如果是非public的，需要临时取消检查，然后再创建对象  
    setAccessible(boolean) 暴力反射

# 四、反射获取成员变量 #

## 1.Class类获取成员变量对象的方法 ##

<table> 
 <thead> 
  <tr> 
   <th>方法名</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Field[] getFields()</td> 
   <td>返回所有公共成员变量对象的数组</td> 
  </tr> 
  <tr> 
   <td>Field[] getDeclaredFields()</td> 
   <td>返回所有成员变量对象的数组</td> 
  </tr> 
  <tr> 
   <td>Field getField(String name)</td> 
   <td>返回单个公共成员变量对象</td> 
  </tr> 
  <tr> 
   <td>Field getDeclaredField(String name)</td> 
   <td>返回单个成员变量对象</td> 
  </tr> 
 </tbody> 
</table>

## 2.Field类用于给成员变量赋值的方法 ##

<table> 
 <thead> 
  <tr> 
   <th>方法名</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>void set(Object obj, Object value)</td> 
   <td>赋值</td> 
  </tr> 
  <tr> 
   <td>Object get(Object obj)</td> 
   <td>获取值</td> 
  </tr> 
 </tbody> 
</table>

Student类

public class Student {
        
    
        public String name;
    
        public int age;
    
        public String gender;
    
        private int money = 300;
    
        @Override
        public String toString() {
        
            return "Student{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    ", gender='" + gender + '\'' +
                    ", money=" + money +
                    '}';
        }
    }

测试类ReflectDemo2

import java.lang.reflect.Field;
    
    public class ReflectDemo2 {
        
        public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException, InstantiationException {
        
            method1();
            method2();
    
        }
    
        private static void method2() throws ClassNotFoundException, NoSuchFieldException, InstantiationException, IllegalAccessException {
        
            Class clazz = Class.forName("csdn.csdn3.Student");
            Field field = clazz.getDeclaredField("money");
            field.setAccessible(true);
            Student student = (Student) clazz.newInstance();
            Object o = field.get(student);
            System.out.println(o);
        }
    
        private static void method1() throws ClassNotFoundException, NoSuchFieldException, InstantiationException, IllegalAccessException {
        
            Class clazz = Class.forName("csdn.csdn3.Student");
            Field field = clazz.getField("name");
            Student student = (Student) clazz.newInstance();
            field.set(student,"zhangsan");
            System.out.println(student);
        }
    }

> Student\{name=‘zhangsan’, age=0, gender=‘null’, money=300\}  
> 300

# 四、反射获取成员方法 #

## 1.Class类获取成员方法对象的方法 ##

<table> 
 <thead> 
  <tr> 
   <th>方法名</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Method[] getMethods()</td> 
   <td>返回所有公共成员方法对象的数组，包括继承的</td> 
  </tr> 
  <tr> 
   <td>Method[] getDeclaredMethods()</td> 
   <td>返回所有成员方法对象的数组，不包括继承的</td> 
  </tr> 
  <tr> 
   <td>Method getMethod(String name, Class&lt;?&gt;… parameterTypes)</td> 
   <td>返回单个公共成员方法对象</td> 
  </tr> 
  <tr> 
   <td>Method getDeclaredMethod(String name, Class&lt;?&gt;… parameterTypes)</td> 
   <td>返回单个成员方法对象</td> 
  </tr> 
 </tbody> 
</table>

## 2.Method类用于执行方法的方法 ##

<table> 
 <thead> 
  <tr> 
   <th>方法名</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Object invoke(Object obj, Object… args)</td> 
   <td>运行方法</td> 
  </tr> 
 </tbody> 
</table>

Student类

public class Student {
        
    
        private void show() {
        
            System.out.println("私有的show方法，无参无返回值");
        }
    
        public void function1() {
        
            System.out.println("function1方法，无参无返回值");
        }
    
        public void function2(String name) {
        
            System.out.println("function2方法，有参无返回值,参数为" + name);
        }
    
        public String function3() {
        
            System.out.println("function3方法，无参有返回值");
            return "aaa";
        }
    
        public String function4(String name) {
        
            System.out.println("function4方法，有参有返回值,参数为" + name);
            return "aaa";
        }
    }

测试类ReflectDemo3

import java.lang.reflect.InvocationTargetException;
    import java.lang.reflect.Method;
    
    public class ReflectDemo3 {
        
        public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InstantiationException, InvocationTargetException {
        
            Class clazz = Class.forName("csdn.csdn3.Student");
            Method method = clazz.getMethod("function4", String.class);
            Student student = (Student) clazz.newInstance();
            Object result = method.invoke(student, "zhangsan");
            System.out.println(result);
        }
    }

> function4方法，有参有返回值,参数为zhangsan  
> aaa

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