What is the principle of java reflection mechanism

Java reflection mechanism principle: 1. For any class, you can know all the properties and methods of this class, and for any object, you can call any of its methods; 2. Everything is an object, and classes It is also an object; 3. When [Animal.class] is on the hard disk, it is a file. When loaded into the memory, it can be considered as an object.

Java reflection mechanism principle:

1. The concept of reflection mechanism:

means that in the running state, for any class, you can know all the properties and methods of this class, and for any object, you can call any of its methods. This kind of dynamic acquisition of information, and dynamic calling of objects The function of the method is called the reflection mechanism of the java language.

2. Application of the reflection mechanism:

Generate dynamic proxy, slice-oriented programming (add before and after calling the method Stack frame).

3. The principle of reflection mechanism:

1. First of all, a clear concept: everything is an object----classes are also objects.

2. Then know the content in the class: modifier constructor field method.

3. Next, understand the loading: When Animal.class is in the hard disk, it is a file. When loaded into the memory, you can It is considered to be an object, an object of java.lang.class.

When running the program, an Animal.class object is generated during instantiation. What is the difference between the two objects?

As shown below , the above Animal.class object is an object of java.lang.class; the following object is an object generated by instantiation of Animal.class

4 . When Animal.class is loaded into the JVM, how does the JVM identify the methods, member variables, construction methods, etc. contained in Animal.class?

As shown below, the member variables in the instantiated object of Animal.class =red;

When loaded into memory, the fur color =null, which is assigned to red when instantiated.

##In Animal.class The coat color attribute is an attribute value of Field for java.lang.class, and the coat color is also an object for java.lang.class. This is also the reason why the reflection mechanism dynamically obtains information and dynamically calls object methods.

The following picture is the method in Java.lang.class

## in java In .lang.class, coat color is an attribute value of Field. All methods, member variables, constructors, and modifiers in Animal are written according to the standards in java.lang.class, otherwise an error will be reported during compilation.

4. Simple example code of radiation mechanism

public class _14_ReflectTest07
{
     public static void main(String[] args) throws Exception{
         //1.获取类
         Class c = Class.forName("_12_CustomerService");
         //获取某个特定的方法
         //通过：方法名+形参列表
         Method m = c.getDeclaredMethod("login",String.class,String.class);
         //通过反射机制执行login方法.
         Object o = c.newInstance();
         //调用o对象的m方法,传递"admin""123"参数，方法的执行结果是retValue
         Object retValue = m.invoke(o, "admin","123");
         System.out.println(retValue); //true
     }
}
 
 
 
public class _12_CustomerService
{
     //登录
     public boolean login(String name,String pwd){
         if("admin".equals(name) && "123".equals(pwd)){
              return true;
         }
         return false;
     }
     //退出
     public void logout(){
         System.out.println("系统已安全退出！");
     }
}

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