What is the principle of Java reflection mechanism?

java The reflection mechanism is implemented through the following mechanisms: The reflection API provides interfaces and classes for accessing and manipulating reflection data. The JVM maintains an internal data structure that contains metadata for all loaded classes. The reflection mechanism performs introspection operations by accessing this data.

The principle of Java reflection mechanism

The Java reflection mechanism allows programs to inspect and modify the structure and behavior of Java classes at runtime. It provides an introspection capability that enables us to load classes, create objects, call methods and get or set field values.

Principle

The reflection mechanism is implemented through the following mechanism:

• Reflection API: Provides a set of interfaces and Classes, such as Class and Method, are used to access and manipulate reflected data.
• Java Virtual Machine (JVM): The JVM maintains an internal data structure that contains metadata for all loaded classes. The reflection mechanism performs introspection operations by accessing this data.

Usage

To use the reflection mechanism, you need to use the Class class. Class The object represents the class being inspected or modified. The Class object can be obtained as follows:

• through ClassName.class, for example: String.class
• PassClass.forName("ClassName")
• Pass Object.getClass()

Practical case

The following is an example of creating an object and calling its methods through the reflection mechanism:

import java.lang.reflect.Class;
import java.lang.reflect.Method;

public class ReflectionDemo {

    public static void main(String[] args) throws Exception {
        // 获取 String 类
        Class<?> stringClass = String.class;

        // 创建 String 对象
        Object stringObject = stringClass.newInstance();

        // 获取 concat 方法
        Method concatMethod = stringClass.getMethod("concat", String.class);

        // 调用 concat 方法
        String result = (String) concatMethod.invoke(stringObject, "World");

        // 打印结果
        System.out.println(result); // 输出: HelloWorld
    }
}

In this example, we obtain String# through String.class ## The Class object of the class. Then, use newInstance() to create a String object. Next, get the Method object of the concat() method and call it, passing an argument and getting the result.

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