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反射机制（动态获取类内部结构和对象内容、调用方法）

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文章目录

Java 进阶: Reflect class="tags" href="/tags/FanShe.html" title=反射>反射机制（动态获取类内部结构和对象内容、调用方法）
- 简介
- 参考
- 完整测试代码地址
正文
- 获取类定义结构
- - 可获取内部信息总览
- 成员变量 Field
- - Field 方法
  - Field 信息
  - Field 动态获取对象内容
- 方法 Method
- - Method 方法
  - Method 信息
  - Method 动态调用方法
- 构造函数 Constructor
- - Constructor 方法
  - Constructor 信息
  - Constructor 动态创建对象实例
结语

简介

前一篇：Java 基础: 浅谈类型基础 - Class 对象带我们初步认识了 Class 对象有关类型的信息，然而我们真正希望做的是透过class="tags" href="/tags/FanShe.html" title=反射>反射动态获取对象中的值或是调用对象的方法。老样子，还是我们的老朋友 Class 对象。

参考

五分钟看懂ClassLoader	https://www.jianshu.com/p/554c138ca0f5
JAVA Reflectclass="tags" href="/tags/FanShe.html" title=反射>反射详解	https://blog.csdn.net/u014209205/article/details/80542114
试用Java中的class="tags" href="/tags/FanShe.html" title=反射>反射reflect之getDeclaredMethods和getMethods	https://www.cnblogs.com/jianjianjiao/articles/1853409.html
Java Field getBoolean()用法及代码示例	https://vimsky.com/examples/usage/field-getboolean-method-in-class="tags" href="/tags/JAVA.html" title=java>java-with-examples.html

完整测试代码地址

先附上文中用上的完整测试代码地址：https://github.com/superfreeeee/Blog-code/tree/main/back_end/class="tags" href="/tags/JAVA.html" title=java>java/class="tags" href="/tags/JAVA.html" title=java>java_reflect

正文

获取类定义结构

前一篇我们演示了如何获取并检查类的各种信息（访问修饰符、类/接口/枚举/注解类型、blablabla），下面我们要来获取类的内部结构

可获取内部信息总览

首先我们先来看看我们可以获取哪些内部信息

Method	Description
Field[] getFields()	获取成员变量列表
Field[] getDeclaredFields()	获取自有成员变量列表
Method[] getMethods()	获取方法列表
Method[] getDeclaredMethods()	获取自有方法列表
Constructor[] getConstructors()	获取构造函数列表
Constructor[] getDeclaredConstructors()	获取自有构造函数列表
Class[] getClasses()	获取内部类列表
Class[] getDeclaredClasses()	获取自有内部类列表

应该可以很清楚的发现四种内容都分为 getXXX 和 getDeclaredXXX 两个方法，其中的差异在于：

getXXX 获取所有从祖先类、接口继承或实现的访问修饰符为 public 的成员
getDeclaredXXX 获取所有该类自己定义的所有(任意描述符)成员

看看下面的用例就知道了

Demo.class="tags" href="/tags/JAVA.html" title=java>java

class="prism language-class="tags" href="/tags/JAVA.html" title=java>java">class="token keyword">package comclass="token punctuation">.exampleclass="token punctuation">.reflectclass="token punctuation">.test1class="token punctuation">;

class="token comment">// 建立不同访问权限的各种成员
class="token keyword">public class="token keyword">class class="token class-name">Demo class="token punctuation">{
    class="token comment">// 成员变量
    class="token keyword">private String privateFieldclass="token punctuation">;
    class="token keyword">protected String protectedFieldclass="token punctuation">;
    String defaultFieldclass="token punctuation">;
    class="token keyword">public String publicFieldclass="token punctuation">;

    class="token comment">// 构造函数
    class="token keyword">private class="token function">Democlass="token punctuation">(class="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">protected class="token function">Democlass="token punctuation">(class="token keyword">int iclass="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token function">Democlass="token punctuation">(class="token keyword">float fclass="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">public class="token function">Democlass="token punctuation">(class="token keyword">double dclass="token punctuation">) class="token punctuation">{class="token punctuation">}

    class="token comment">// 方法
    class="token keyword">private class="token keyword">void class="token function">privateMethodclass="token punctuation">(class="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">protected class="token keyword">void class="token function">protectedMethodclass="token punctuation">(class="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">void class="token function">defaultMethodclass="token punctuation">(class="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">public class="token keyword">void class="token function">publicMethodclass="token punctuation">(class="token punctuation">) class="token punctuation">{class="token punctuation">}

    class="token comment">// 内部类
    class="token keyword">private class="token keyword">class class="token class-name">PrivateInnerClass class="token punctuation">{class="token punctuation">}
    class="token keyword">protected class="token keyword">class class="token class-name">ProtectedInnerClass class="token punctuation">{class="token punctuation">}
    class="token keyword">class class="token class-name">DefaultInnerClass class="token punctuation">{class="token punctuation">}
    class="token keyword">public class="token keyword">class class="token class-name">PublicInnerClass class="token punctuation">{class="token punctuation">}
class="token punctuation">}

Test.class="tags" href="/tags/JAVA.html" title=java>java

class="prism language-class="tags" href="/tags/JAVA.html" title=java>java">class="token keyword">package comclass="token punctuation">.exampleclass="token punctuation">.reflectclass="token punctuation">.test1class="token punctuation">;

class="token keyword">import class="tags" href="/tags/JAVA.html" title=java>javaclass="token punctuation">.langclass="token punctuation">.reflectclass="token punctuation">.Constructorclass="token punctuation">;
class="token keyword">import class="tags" href="/tags/JAVA.html" title=java>javaclass="token punctuation">.langclass="token punctuation">.reflectclass="token punctuation">.Fieldclass="token punctuation">;
class="token keyword">import class="tags" href="/tags/JAVA.html" title=java>javaclass="token punctuation">.langclass="token punctuation">.reflectclass="token punctuation">.Methodclass="token punctuation">;
class="token keyword">import class="tags" href="/tags/JAVA.html" title=java>javaclass="token punctuation">.utilclass="token punctuation">.Arraysclass="token punctuation">;

class="token keyword">public class="token keyword">class class="token class-name">Test class="token punctuation">{
    class="token keyword">public class="token keyword">static class="token keyword">void class="token function">mainclass="token punctuation">(Stringclass="token punctuation">[class="token punctuation">] argsclass="token punctuation">) class="token punctuation">{
        Classclass="token generics function">class="token punctuation"><Democlass="token punctuation">> demoClass class="token operator">= Democlass="token punctuation">.class="token keyword">classclass="token punctuation">;

        class="token comment">// 查询成员变量
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- Demo fields ----- "class="token punctuation">)class="token punctuation">;
        class="token keyword">forclass="token punctuation">(Field field class="token operator">: demoClassclass="token punctuation">.class="token function">getFieldsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
            Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"field: " class="token operator">+ fieldclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">) class="token operator">+ class="token string">", type: " class="token operator">+ fieldclass="token punctuation">.class="token function">getTypeclass="token punctuation">(class="token punctuation">)class="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        class="token punctuation">}
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- Demo declared fields ----- "class="token punctuation">)class="token punctuation">;
        class="token keyword">forclass="token punctuation">(Field field class="token operator">: demoClassclass="token punctuation">.class="token function">getDeclaredFieldsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
            Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"field: " class="token operator">+ fieldclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">) class="token operator">+ class="token string">", type: " class="token operator">+ fieldclass="token punctuation">.class="token function">getTypeclass="token punctuation">(class="token punctuation">)class="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        class="token punctuation">}
        class="token comment">// 查询方法
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- Demo methods ----- "class="token punctuation">)class="token punctuation">;
        class="token keyword">forclass="token punctuation">(Method method class="token operator">: demoClassclass="token punctuation">.class="token function">getMethodsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
            Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"method: " class="token operator">+ methodclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">) class="token operator">+ class="token string">", params: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(methodclass="token punctuation">.class="token function">getParameterTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
        class="token punctuation">}
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- Demo declared methods ----- "class="token punctuation">)class="token punctuation">;
        class="token keyword">forclass="token punctuation">(Method method class="token operator">: demoClassclass="token punctuation">.class="token function">getDeclaredMethodsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
            Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"method: " class="token operator">+ methodclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">) class="token operator">+ class="token string">", params: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(methodclass="token punctuation">.class="token function">getParameterTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
        class="token punctuation">}
        class="token comment">// 查询构造函数
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- Demo constructors ----- "class="token punctuation">)class="token punctuation">;
        class="token keyword">forclass="token punctuation">(Constructor constructor class="token operator">: demoClassclass="token punctuation">.class="token function">getConstructorsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
            Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"constructor: " class="token operator">+ constructorclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">) class="token operator">+ class="token string">", params: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(constructorclass="token punctuation">.class="token function">getParameterTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
        class="token punctuation">}
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- Demo declared constructors ----- "class="token punctuation">)class="token punctuation">;
        class="token keyword">forclass="token punctuation">(Constructor constructor class="token operator">: demoClassclass="token punctuation">.class="token function">getDeclaredConstructorsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
            Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"constructor: " class="token operator">+ constructorclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">) class="token operator">+ class="token string">", params: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(constructorclass="token punctuation">.class="token function">getParameterTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
        class="token punctuation">}
        class="token comment">// 查询内部类
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- Demo classes ----- "class="token punctuation">)class="token punctuation">;
        class="token keyword">forclass="token punctuation">(Class class="token class-name">c class="token operator">: demoClassclass="token punctuation">.class="token function">getClassesclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
            Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"class: " class="token operator">+ cclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">) class="token operator">+ class="token string">", modifiers: " class="token operator">+ cclass="token punctuation">.class="token function">getModifiersclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        class="token punctuation">}
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- Demo declared classes ----- "class="token punctuation">)class="token punctuation">;
        class="token keyword">forclass="token punctuation">(Class class="token class-name">c class="token operator">: demoClassclass="token punctuation">.class="token function">getDeclaredClassesclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
            Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"class: " class="token operator">+ cclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">) class="token operator">+ class="token string">", modifiers: " class="token operator">+ cclass="token punctuation">.class="token function">getModifiersclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        class="token punctuation">}
    class="token punctuation">}
class="token punctuation">}

输出

----- Demo fields ----- 
field: publicField, type: class="tags" href="/tags/JAVA.html" title=java>java.lang.String
----- Demo declared fields ----- 
field: privateField, type: class="tags" href="/tags/JAVA.html" title=java>java.lang.String
field: protectedField, type: class="tags" href="/tags/JAVA.html" title=java>java.lang.String
field: defaultField, type: class="tags" href="/tags/JAVA.html" title=java>java.lang.String
field: publicField, type: class="tags" href="/tags/JAVA.html" title=java>java.lang.String
----- Demo methods ----- 
method: publicMethod, params: []
method: wait, params: [long, int]
method: wait, params: [long]
method: wait, params: []
method: equals, params: [class class="tags" href="/tags/JAVA.html" title=java>java.lang.Object]
method: toString, params: []
method: hashCode, params: []
method: getClass, params: []
method: notify, params: []
method: notifyAll, params: []
----- Demo declared methods ----- 
method: privateMethod, params: []
method: protectedMethod, params: []
method: defaultMethod, params: []
method: publicMethod, params: []
----- Demo constructors ----- 
constructor: com.example.reflect.test1.Demo, params: [double]
----- Demo declared constructors ----- 
constructor: com.example.reflect.test1.Demo, params: []
constructor: com.example.reflect.test1.Demo, params: [int]
constructor: com.example.reflect.test1.Demo, params: [float]
constructor: com.example.reflect.test1.Demo, params: [double]
----- Demo classes ----- 
class: com.example.reflect.test1.Demo$PublicInnerClass, modifiers: 1
----- Demo declared classes ----- 
class: com.example.reflect.test1.Demo$PublicInnerClass, modifiers: 1
class: com.example.reflect.test1.Demo$DefaultInnerClass, modifiers: 0
class: com.example.reflect.test1.Demo$ProtectedInnerClass, modifiers: 4
class: com.example.reflect.test1.Demo$PrivateInnerClass, modifiers: 2

下面我们将对前三种成员类型一一说明（第四种就是内部的 Class 类型，与一般的 Class 对象无异）

成员变量 Field

第一种成员类型是成员变量，定义为 class="tags" href="/tags/JAVA.html" title=java>java.lang.reflect.Field 类型

Field 方法

首先先来看看 Field 可以调用的方法接口

Method	Usage
String getName()	获取变量名
Class getType()、Type getGenericType()	获取变量类型
Class getDeclaringClass()	获取成员所属类型
int getModifiers()	获取变量访问修饰符
T getT(Object)	动态获取参数对象实际成员变量值

Field 信息

FieldDemo.class="tags" href="/tags/JAVA.html" title=java>java：成员变量示例类型

class="prism language-class="tags" href="/tags/JAVA.html" title=java>java">class="token keyword">package comclass="token punctuation">.exampleclass="token punctuation">.reflectclass="token punctuation">.test2class="token punctuation">;

class="token keyword">public class="token keyword">class class="token class-name">FieldDemo class="token punctuation">{
    class="token keyword">private class="token keyword">int privateIntclass="token punctuation">; class="token comment">// private 变量
    class="token keyword">protected class="token keyword">int protectedIntclass="token punctuation">; class="token comment">// protected 变量
    class="token keyword">int defaultIntclass="token punctuation">; class="token comment">// default 变量
    class="token keyword">public class="token keyword">int publicIntclass="token punctuation">; class="token comment">// public 变量
    class="token keyword">public class="token keyword">static class="token keyword">int publicStaticIntclass="token punctuation">; class="token comment">// public static 变量

    class="token keyword">private String stringFieldclass="token punctuation">; class="token comment">// String 类型
    class="token keyword">private Object objectFieldclass="token punctuation">; class="token comment">// Object 类型
    class="token keyword">private class="token keyword">intclass="token punctuation">[class="token punctuation">] arrayFiledclass="token punctuation">; class="token comment">// 数组类型

class="token punctuation">}

测试方法

class="prism language-class="tags" href="/tags/JAVA.html" title=java>java">class="token keyword">void class="token function">testFieldInfoclass="token punctuation">(class="token punctuation">) class="token punctuation">{
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"##### testFieldInfo #####"class="token punctuation">)class="token punctuation">;
    Classclass="token generics function">class="token punctuation"><FieldDemoclass="token punctuation">> fieldDemoClass class="token operator">= FieldDemoclass="token punctuation">.class="token keyword">classclass="token punctuation">;

    class="token comment">// getFields
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- fields ----- "class="token punctuation">)class="token punctuation">;
    class="token keyword">for class="token punctuation">(Field field class="token operator">: fieldDemoClassclass="token punctuation">.class="token function">getFieldsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(fieldclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
    class="token punctuation">}
    class="token comment">// getDeclaredFields
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- declared fields ----- "class="token punctuation">)class="token punctuation">;
    class="token keyword">forclass="token punctuation">(Field field class="token operator">: fieldDemoClassclass="token punctuation">.class="token function">getDeclaredFieldsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(fieldclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
    class="token punctuation">}
    class="token comment">// fields detail
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- declared fields detail ----- "class="token punctuation">)class="token punctuation">;
    class="token keyword">forclass="token punctuation">(Field field class="token operator">: fieldDemoClassclass="token punctuation">.class="token function">getDeclaredFieldsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"name: " class="token operator">+ fieldclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\ttype: " class="token operator">+ fieldclass="token punctuation">.class="token function">getTypeclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tgenericType: " class="token operator">+ fieldclass="token punctuation">.class="token function">getGenericTypeclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tdeclaringClass: " class="token operator">+ fieldclass="token punctuation">.class="token function">getDeclaringClassclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tmodifiers: " class="token operator">+ fieldclass="token punctuation">.class="token function">getModifiersclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
    class="token punctuation">}
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token punctuation">)class="token punctuation">;
class="token punctuation">}

输出

##### testFieldInfo #####
----- fields ----- 
publicInt
publicStaticInt
----- declared fields ----- 
privateInt
protectedInt
defaultInt
publicInt
publicStaticInt
stringField
objectField
arrayFiled
----- declared fields detail ----- 
name: privateInt
	type: int
	genericType: int
	declaringClass: class com.example.reflect.test2.FieldDemo
	modifiers: 2
name: protectedInt
	type: int
	genericType: int
	declaringClass: class com.example.reflect.test2.FieldDemo
	modifiers: 4
name: defaultInt
	type: int
	genericType: int
	declaringClass: class com.example.reflect.test2.FieldDemo
	modifiers: 0
name: publicInt
	type: int
	genericType: int
	declaringClass: class com.example.reflect.test2.FieldDemo
	modifiers: 1
name: publicStaticInt
	type: int
	genericType: int
	declaringClass: class com.example.reflect.test2.FieldDemo
	modifiers: 9
name: stringField
	type: class class="tags" href="/tags/JAVA.html" title=java>java.lang.String
	genericType: class class="tags" href="/tags/JAVA.html" title=java>java.lang.String
	declaringClass: class com.example.reflect.test2.FieldDemo
	modifiers: 2
name: objectField
	type: class class="tags" href="/tags/JAVA.html" title=java>java.lang.Object
	genericType: class class="tags" href="/tags/JAVA.html" title=java>java.lang.Object
	declaringClass: class com.example.reflect.test2.FieldDemo
	modifiers: 2
name: arrayFiled
	type: class [I
	genericType: class [I
	declaringClass: class com.example.reflect.test2.FieldDemo
	modifiers: 2

Field 动态获取对象内容

测试方法

class="prism language-class="tags" href="/tags/JAVA.html" title=java>java">class="token keyword">void class="token function">extractFieldInfoclass="token punctuation">(class="token punctuation">) class="token keyword">throws NoSuchFieldExceptionclass="token punctuation">, IllegalAccessException class="token punctuation">{
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"##### extractFieldInfo #####"class="token punctuation">)class="token punctuation">;
    FieldDemo demo1 class="token operator">= class="token keyword">new class="token class-name">FieldDemoclass="token punctuation">(class="token punctuation">)class="token punctuation">;
    demo1class="token punctuation">.publicInt class="token operator">= class="token number">1class="token punctuation">;
    FieldDemo demo2 class="token operator">= class="token keyword">new class="token class-name">FieldDemoclass="token punctuation">(class="token punctuation">)class="token punctuation">;
    demo2class="token punctuation">.publicInt class="token operator">= class="token number">2class="token punctuation">;

    Classclass="token generics function">class="token punctuation"><FieldDemoclass="token punctuation">> fieldDemoClass class="token operator">= FieldDemoclass="token punctuation">.class="token keyword">classclass="token punctuation">;
    Field publicInt class="token operator">= fieldDemoClassclass="token punctuation">.class="token function">getDeclaredFieldclass="token punctuation">(class="token string">"publicInt"class="token punctuation">)class="token punctuation">; class="token comment">// throws NoSuchFieldException
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"demo1.publicInt: " class="token operator">+ publicIntclass="token punctuation">.class="token function">getIntclass="token punctuation">(demo1class="token punctuation">)class="token punctuation">)class="token punctuation">;
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"demo2.publicInt: " class="token operator">+ publicIntclass="token punctuation">.class="token function">getIntclass="token punctuation">(demo2class="token punctuation">)class="token punctuation">)class="token punctuation">;
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token punctuation">)class="token punctuation">;
class="token punctuation">}

输出

##### extractFieldInfo #####
demo1.publicInt: 1
demo2.publicInt: 2

方法 Method

第二种是方法，定义为 class="tags" href="/tags/JAVA.html" title=java>java.lang.reflect.Method

Method 方法

Method	Usage
String getName()	获取方法名
Class getReturnType()、Type getGenericReturnType()	获取返回类型
Class[] getParameterTypes()、Type[] getGenericParameterTypes()	获取参数类型列表
Class[] getExceptionTypes()、Type[] getGenericExceptionTypes()	获取抛出异常类型列表
Class getDeclaringClass()	获取定义方法的类
Object getDefaultValue()	获取默认返回值
int getModifiers()	获取方法访问修饰符
void setAccessible(boolean)	设置调用时访问权限
Object invoke(Object, Object …args)	传入调用方法对象和参数列表，调用函数

Method 信息

MethodDemo.class="tags" href="/tags/JAVA.html" title=java>java

class="prism language-class="tags" href="/tags/JAVA.html" title=java>java">class="token keyword">package comclass="token punctuation">.exampleclass="token punctuation">.reflectclass="token punctuation">.test3class="token punctuation">;

class="token keyword">public class="token keyword">class class="token class-name">MethodDemo class="token punctuation">{

    class="token keyword">private String nameclass="token punctuation">;

    class="token keyword">public class="token function">MethodDemoclass="token punctuation">(String nameclass="token punctuation">) class="token punctuation">{
        class="token keyword">thisclass="token punctuation">.name class="token operator">= nameclass="token punctuation">;
    class="token punctuation">}

    class="token keyword">private class="token keyword">void class="token function">privateMethodclass="token punctuation">(class="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">protected class="token keyword">void class="token function">protectedMethodclass="token punctuation">(class="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">void class="token function">defaultMethodclass="token punctuation">(class="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">public class="token keyword">void class="token function">publicMethodclass="token punctuation">(class="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">public class="token keyword">static class="token keyword">void class="token function">publicStaticMethodclass="token punctuation">(class="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">private class="token keyword">void class="token function">privateMethodWithParamsclass="token punctuation">(class="token keyword">int iclass="token punctuation">, class="token keyword">int jclass="token punctuation">) class="token punctuation">{
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"invoke privateMethodWithParams from object: [name=" class="token operator">+ name class="token operator">+ class="token string">"], with params: [i=" class="token operator">+ i class="token operator">+ class="token string">", j=" class="token operator">+ j class="token operator">+ class="token string">"]"class="token punctuation">)class="token punctuation">;
    class="token punctuation">}
    class="token keyword">void class="token function">defaultMethodWithExceptionsclass="token punctuation">(class="token punctuation">) class="token keyword">throws NoSuchMethodExceptionclass="token punctuation">, IllegalArgumentException class="token punctuation">{class="token punctuation">}
class="token punctuation">}

测试方法

class="prism language-class="tags" href="/tags/JAVA.html" title=java>java">class="token keyword">void class="token function">testMethodInfoclass="token punctuation">(class="token punctuation">) class="token punctuation">{
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"##### testMethodInfo #####"class="token punctuation">)class="token punctuation">;
    Classclass="token generics function">class="token punctuation"><MethodDemoclass="token punctuation">> c class="token operator">= MethodDemoclass="token punctuation">.class="token keyword">classclass="token punctuation">;
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- methods -----"class="token punctuation">)class="token punctuation">;
    class="token keyword">for class="token punctuation">(Method method class="token operator">: cclass="token punctuation">.class="token function">getMethodsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(methodclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
    class="token punctuation">}

    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- declared methods -----"class="token punctuation">)class="token punctuation">;
    class="token keyword">for class="token punctuation">(Method method class="token operator">: cclass="token punctuation">.class="token function">getDeclaredMethodsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(methodclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
    class="token punctuation">}

    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- declared methods detail -----"class="token punctuation">)class="token punctuation">;
    class="token keyword">for class="token punctuation">(Method method class="token operator">: cclass="token punctuation">.class="token function">getDeclaredMethodsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"name: " class="token operator">+ methodclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\treturnType: " class="token operator">+ methodclass="token punctuation">.class="token function">getReturnTypeclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tgenericReturnType: " class="token operator">+ methodclass="token punctuation">.class="token function">getGenericReturnTypeclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tparameterTypes: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(methodclass="token punctuation">.class="token function">getParameterTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tgenericParameterTypes: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(methodclass="token punctuation">.class="token function">getGenericParameterTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\texceptionTypes: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(methodclass="token punctuation">.class="token function">getExceptionTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tgenericExceptionTypes: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(methodclass="token punctuation">.class="token function">getGenericExceptionTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tdeclaringClass: " class="token operator">+ methodclass="token punctuation">.class="token function">getDeclaringClassclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tdefaultValue: " class="token operator">+ methodclass="token punctuation">.class="token function">getDefaultValueclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tmodifiers: " class="token operator">+ methodclass="token punctuation">.class="token function">getModifiersclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
    class="token punctuation">}

    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token punctuation">)class="token punctuation">;
class="token punctuation">}

输出

##### testMethodInfo #####
----- methods -----
publicMethod
publicStaticMethod
wait
wait
wait
equals
toString
hashCode
getClass
notify
notifyAll
----- declared methods -----
privateMethod
protectedMethod
privateMethodWithParams
defaultMethod
publicMethod
publicStaticMethod
defaultMethodWithExceptions
----- declared methods detail -----
name: privateMethod
	returnType: void
	genericReturnType: void
	parameterTypes: []
	genericParameterTypes: []
	exceptionTypes: []
	genericExceptionTypes: []
	declaringClass: class com.example.reflect.test3.MethodDemo
	defaultValue: null
	modifiers: 2
name: protectedMethod
	returnType: void
	genericReturnType: void
	parameterTypes: []
	genericParameterTypes: []
	exceptionTypes: []
	genericExceptionTypes: []
	declaringClass: class com.example.reflect.test3.MethodDemo
	defaultValue: null
	modifiers: 4
name: privateMethodWithParams
	returnType: void
	genericReturnType: void
	parameterTypes: [int, int]
	genericParameterTypes: [int, int]
	exceptionTypes: []
	genericExceptionTypes: []
	declaringClass: class com.example.reflect.test3.MethodDemo
	defaultValue: null
	modifiers: 2
name: defaultMethod
	returnType: void
	genericReturnType: void
	parameterTypes: []
	genericParameterTypes: []
	exceptionTypes: []
	genericExceptionTypes: []
	declaringClass: class com.example.reflect.test3.MethodDemo
	defaultValue: null
	modifiers: 0
name: publicMethod
	returnType: void
	genericReturnType: void
	parameterTypes: []
	genericParameterTypes: []
	exceptionTypes: []
	genericExceptionTypes: []
	declaringClass: class com.example.reflect.test3.MethodDemo
	defaultValue: null
	modifiers: 1
name: publicStaticMethod
	returnType: void
	genericReturnType: void
	parameterTypes: []
	genericParameterTypes: []
	exceptionTypes: []
	genericExceptionTypes: []
	declaringClass: class com.example.reflect.test3.MethodDemo
	defaultValue: null
	modifiers: 9
name: defaultMethodWithExceptions
	returnType: void
	genericReturnType: void
	parameterTypes: []
	genericParameterTypes: []
	exceptionTypes: [class class="tags" href="/tags/JAVA.html" title=java>java.lang.NoSuchMethodException, class class="tags" href="/tags/JAVA.html" title=java>java.lang.IllegalArgumentException]
	genericExceptionTypes: [class class="tags" href="/tags/JAVA.html" title=java>java.lang.NoSuchMethodException, class class="tags" href="/tags/JAVA.html" title=java>java.lang.IllegalArgumentException]
	declaringClass: class com.example.reflect.test3.MethodDemo
	defaultValue: null
	modifiers: 0

Method 动态调用方法

测试方法

class="prism language-class="tags" href="/tags/JAVA.html" title=java>java">class="token keyword">void class="token function">invokeMethodclass="token punctuation">(class="token punctuation">) class="token keyword">throws NoSuchMethodExceptionclass="token punctuation">, IllegalAccessExceptionclass="token punctuation">, InvocationTargetException class="token punctuation">{
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"##### invokeMethod #####"class="token punctuation">)class="token punctuation">;
    MethodDemo demo1 class="token operator">= class="token keyword">new class="token class-name">MethodDemoclass="token punctuation">(class="token string">"demo1"class="token punctuation">)class="token punctuation">;
    MethodDemo demo2 class="token operator">= class="token keyword">new class="token class-name">MethodDemoclass="token punctuation">(class="token string">"demo2"class="token punctuation">)class="token punctuation">;

    Classclass="token generics function">class="token punctuation"><MethodDemoclass="token punctuation">> c class="token operator">= MethodDemoclass="token punctuation">.class="token keyword">classclass="token punctuation">;
    Method m class="token operator">= cclass="token punctuation">.class="token function">getDeclaredMethodclass="token punctuation">(class="token string">"privateMethodWithParams"class="token punctuation">, class="token keyword">intclass="token punctuation">.class="token keyword">classclass="token punctuation">, class="token keyword">intclass="token punctuation">.class="token keyword">classclass="token punctuation">)class="token punctuation">;
    mclass="token punctuation">.class="token function">setAccessibleclass="token punctuation">(class="token boolean">trueclass="token punctuation">)class="token punctuation">; class="token comment">// 方法内部引用私有变量，需要设置 setAccessible(true) 才能正常调用
    mclass="token punctuation">.class="token function">invokeclass="token punctuation">(demo1class="token punctuation">, class="token number">10class="token punctuation">, class="token number">20class="token punctuation">)class="token punctuation">;
    mclass="token punctuation">.class="token function">invokeclass="token punctuation">(demo2class="token punctuation">, class="token number">30class="token punctuation">, class="token number">40class="token punctuation">)class="token punctuation">;
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token punctuation">)class="token punctuation">;
class="token punctuation">}

输出

##### invokeMethod #####
invoke privateMethodWithParams from object: [name=demo1], with params: [i=10, j=20]
invoke privateMethodWithParams from object: [name=demo2], with params: [i=30, j=40]

构造函数 Constructor

第三种是构造函数，定义为 class="tags" href="/tags/JAVA.html" title=java>java.lang.reflect.Constructor

Constructor 方法

Method	Usage
String getName()	构造函数名（类名）
Class[] getParameterTypes()、Type[] getGenericParameterTypes()	获取参数列表
int getModifiers()	获取访问修饰符

Constructor 信息

ConstructorDemo.class="tags" href="/tags/JAVA.html" title=java>java

class="prism language-class="tags" href="/tags/JAVA.html" title=java>java">class="token keyword">package comclass="token punctuation">.exampleclass="token punctuation">.reflectclass="token punctuation">.test4class="token punctuation">;

class="token keyword">public class="token keyword">class class="token class-name">ConstructorDemo class="token punctuation">{
    class="token keyword">private class="token function">ConstructorDemoclass="token punctuation">(class="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">protected class="token function">ConstructorDemoclass="token punctuation">(class="token keyword">int iclass="token punctuation">) class="token punctuation">{
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"create ConstructorDemo with i=" class="token operator">+ iclass="token punctuation">)class="token punctuation">;
    class="token punctuation">}
    class="token function">ConstructorDemoclass="token punctuation">(class="token keyword">float fclass="token punctuation">) class="token punctuation">{class="token punctuation">}
    class="token keyword">public class="token function">ConstructorDemoclass="token punctuation">(class="token keyword">double dclass="token punctuation">) class="token punctuation">{class="token punctuation">}
class="token punctuation">}

测试方法

class="prism language-class="tags" href="/tags/JAVA.html" title=java>java">class="token keyword">void class="token function">testConstructorInfoclass="token punctuation">(class="token punctuation">) class="token punctuation">{
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"##### testConstructorInfo #####"class="token punctuation">)class="token punctuation">;
    Classclass="token generics function">class="token punctuation"><ConstructorDemoclass="token punctuation">> c class="token operator">= ConstructorDemoclass="token punctuation">.class="token keyword">classclass="token punctuation">;
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- constructors -----"class="token punctuation">)class="token punctuation">;
    class="token keyword">for class="token punctuation">(Constructor constructor class="token operator">: cclass="token punctuation">.class="token function">getConstructorsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(constructorclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">) class="token operator">+ class="token string">", params: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(constructorclass="token punctuation">.class="token function">getParameterTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
    class="token punctuation">}

    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- declared constructors -----"class="token punctuation">)class="token punctuation">;
    class="token keyword">for class="token punctuation">(Constructor constructor class="token operator">: cclass="token punctuation">.class="token function">getDeclaredConstructorsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(constructorclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">) class="token operator">+ class="token string">", params: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(constructorclass="token punctuation">.class="token function">getParameterTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
    class="token punctuation">}

    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"----- declared constructors detail -----"class="token punctuation">)class="token punctuation">;
    class="token keyword">for class="token punctuation">(Constructor constructor class="token operator">: cclass="token punctuation">.class="token function">getDeclaredConstructorsclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token punctuation">{
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"name: " class="token operator">+ constructorclass="token punctuation">.class="token function">getNameclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tparameterTypes: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(constructorclass="token punctuation">.class="token function">getParameterTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tgenericParameterTypes: " class="token operator">+ Arraysclass="token punctuation">.class="token function">toStringclass="token punctuation">(constructorclass="token punctuation">.class="token function">getGenericParameterTypesclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">)class="token punctuation">;
        Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"\tmodifiers: " class="token operator">+ constructorclass="token punctuation">.class="token function">getModifiersclass="token punctuation">(class="token punctuation">)class="token punctuation">)class="token punctuation">;
    class="token punctuation">}

    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token punctuation">)class="token punctuation">;
class="token punctuation">}

输出

##### testConstructorInfo #####
----- constructors -----
com.example.reflect.test4.ConstructorDemo, params: [double]
----- declared constructors -----
com.example.reflect.test4.ConstructorDemo, params: [double]
com.example.reflect.test4.ConstructorDemo, params: [float]
com.example.reflect.test4.ConstructorDemo, params: [int]
com.example.reflect.test4.ConstructorDemo, params: []
----- declared constructors detail -----
name: com.example.reflect.test4.ConstructorDemo
	parameterTypes: [double]
	genericParameterTypes: [double]
	modifiers: 1
name: com.example.reflect.test4.ConstructorDemo
	parameterTypes: [float]
	genericParameterTypes: [float]
	modifiers: 0
name: com.example.reflect.test4.ConstructorDemo
	parameterTypes: [int]
	genericParameterTypes: [int]
	modifiers: 4
name: com.example.reflect.test4.ConstructorDemo
	parameterTypes: []
	genericParameterTypes: []
	modifiers: 2

Constructor 动态创建对象实例

测试方法

class="prism language-class="tags" href="/tags/JAVA.html" title=java>java">class="token keyword">void class="token function">invokeConstructorclass="token punctuation">(class="token punctuation">) class="token keyword">throws NoSuchMethodExceptionclass="token punctuation">, InstantiationExceptionclass="token punctuation">, IllegalAccessExceptionclass="token punctuation">, InvocationTargetException class="token punctuation">{
    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token string">"##### invokeConstructor #####"class="token punctuation">)class="token punctuation">;

    Classclass="token generics function">class="token punctuation"><ConstructorDemoclass="token punctuation">> c class="token operator">= ConstructorDemoclass="token punctuation">.class="token keyword">classclass="token punctuation">;
    Constructor constructor class="token operator">= cclass="token punctuation">.class="token function">getDeclaredConstructorclass="token punctuation">(class="token keyword">intclass="token punctuation">.class="token keyword">classclass="token punctuation">)class="token punctuation">;
    ConstructorDemo demo1 class="token operator">= cclass="token punctuation">.class="token function">castclass="token punctuation">(constructorclass="token punctuation">.class="token function">newInstanceclass="token punctuation">(class="token number">1class="token punctuation">)class="token punctuation">)class="token punctuation">;
    ConstructorDemo demo2 class="token operator">= cclass="token punctuation">.class="token function">castclass="token punctuation">(constructorclass="token punctuation">.class="token function">newInstanceclass="token punctuation">(class="token number">2class="token punctuation">)class="token punctuation">)class="token punctuation">;

    Systemclass="token punctuation">.outclass="token punctuation">.class="token function">printlnclass="token punctuation">(class="token punctuation">)class="token punctuation">;
class="token punctuation">}

输出

##### invokeConstructor #####
create ConstructorDemo with i=1
create ConstructorDemo with i=2

本人自认为代码注释的很清楚了，见文知义，就不多加解释了

结语

呼终于搞定，中间输出了很多很多信息，Field、Method、Constructor、Class 等都拥有很多附带信息，这些类型相当于是把 .class 文件的类型信息都暴露出来，所以真正应用的时候可以选需要检查的部分和方法即可。

而这也是 Spring 框架中实现依赖注入(DI = Dependency Injection) 的底层原理，距离 Spring 实现原理有更进一步了，下一篇将要从 Spring Boot 的注解切入，先来看看 Java 原生的注解具备什么样的能力，来了解在 Spring 启动过程中所扮演的角色。

Java 进阶: Reflect 反射机制（动态获取类内部结构和对象内容、调用方法）

Java 进阶: Reflect class="tags" href="/tags/FanShe.html" title=反射>反射机制（动态获取类内部结构和对象内容、调用方法）

文章目录

简介

参考

完整测试代码地址

正文

获取类定义结构

可获取内部信息总览

成员变量 Field

Field 方法

Field 信息

Field 动态获取对象内容

方法 Method

Method 方法

Method 信息

Method 动态调用方法

构造函数 Constructor

Constructor 方法

Constructor 信息

Constructor 动态创建对象实例

结语

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