Introduction and application of Java reflection library principles

Introduction and application of Java reflection library principles Java reflection refers to the mechanism that dynamically obtains and operates information during operation.It allows programs to check class, interfaces, fields and methods during runtime, and can instantiate objects, call methods, operating attributes, etc. at runtime.The Java reflection library provides a set of APIs to implement these functions, including reflex classes, methods, fields, constructors, and annotations. The principle of the Java reflection library is mainly achieved by using the Java's reflection API.Reflective API provides some classes, such as Class, Method, Field, etc., can obtain and operate information through these classes. First, you can obtain class information through the Class class.Through the full -limited name or object reference of the class, you can use the class.Forname () method to obtain a class class object.Through the Class object, you can obtain information such as constructing functions, methods, fields, fathers, interfaces and other information. By obtaining the constructor, method and field of the class, it can be instantiated, method calls and attribute operations.The newInstance () method of the Constructor class can instantiate an object.A method can be called through the INVOKE () method of the METHOD class.You can get and set a attribute value through the Get () and Set () methods of the Field class. The Java reflection library can also be used to handle annotations.Through the annotation of the class, methods, and fields, the relevant processing can be performed according to the information of the annotation.For example, functions such as automatic mapping, authority control and log records can be achieved by annotations. The application of the Java reflection library is very wide.It can be used to achieve some universal frameworks and tools, such as the ORM framework, IOC container, AOP framework, etc.By reflection, you can realize a strong scalability program design, so that the program can dynamically load the class and call methods, and can change the behavior of the program according to the configuration file or the input of the user. The following is an example that demonstrates how to use the Java reflection library to dynamically call a class: import java.lang.reflect.Method; public class ReflectionExample { public static void main(String[] args) throws Exception { // Obtain the Class object according to the class name Class<?> clazz = Class.forName("com.example.MyClass"); // The method of obtaining method is "MyMethod" method Method method = clazz.getMethod("myMethod"); // Create an object instance Object object = clazz.getConstructor().newInstance(); // Call method method.invoke(object); } } class MyClass { public void myMethod() { System.out.println("Hello, Reflection!"); } } In the above example, the class.Forname () method was obtained by the class.Forname () method, and then the method named "MyMethod" was obtained using the GetMethod () method.Next, a object is instantiated with getConStructor (). NewInstance () and calls this method through the Invoke () method. Through the Java reflection library, we can dynamically obtain and operate information at runtime, which provides great convenience for the flexibility and scalability of the program.However, it should be noted that because the reflection involves the operation of the class, it may bring performance consumption, so it is necessary to use it carefully in the scenes with higher performance requirements.