How to use Reflection function in Java for reflection operations

The Reflection function in Java is an advanced programming technology that can obtain class information and dynamically modify it at runtime. Reflection functions allow us to use its objects and the properties and methods of the class they belong to without knowing the complete information about the class. In this article, we will learn how to perform reflection operations using the Reflection function in Java.

1. Basic concepts of reflection mechanism

The reflection mechanism refers to a mechanism that dynamically obtains class file (.class file) information during the programming process. It allows operating these class file information at runtime, including reading class methods, properties, constructors, getting and calling methods, etc.

In general, the reflection mechanism is that the Java programming language determines the type of an object at runtime, allowing us to check the class to which an object belongs at runtime and analyze its characteristics and behavior.

The main advantage of the reflection mechanism is that it can implement generic code that can be applied to all Java classes without knowing complete information about the actual class. This allows programmers to create, parse, and use objects, properties, and methods in classes through reflection.

2. Obtain the Class object

The first step in reflection is to obtain the Class object of the class, which can be achieved in the following three ways:

1. Use Class. The forName() method gets

This is the most common way to use the reflection mechanism. We can use the Class.forName() method in reflection to obtain the Class object of the class. This method needs to pass in the complete name of a class, for example:

Class clazz = Class.forName("java.lang.String");

2. Use the class name directly.class keyword to obtain

We can also use the class name directly. The class keyword gets the Class object of the class, for example:

Class clazz = String.class;

3. Get it through the getClass() method of the object

We can get it using the getClass() method of the object The Class object of the class to which the object belongs, for example:

String str = "Hello, World!";
Class clazz = str.getClass();

3. Obtain class information

Obtaining class information is the most basic operation in reflection, which allows us to obtain it at runtime Class methods, attributes, constructors and other information, and call and modify them.

We can use the following code to get the information of the class:

1. Get all the constructors of the class

Constructor[] constructors = clazz.getDeclaredConstructors();
for (Constructor constructor : constructors) {
    System.out.println(constructor);
}

2. Get all the methods of the class

Method[] methods = clazz.getDeclaredMethods();
for (Method method : methods) {
    System.out.println(method);
}

3. Get all the attributes of the class

Field[] fields = clazz.getDeclaredFields();
for (Field field : fields) {
    System.out.println(field);
}

4. Manipulate the objects, methods and properties of the class

We can use the reflection mechanism to Use objects, methods, and properties of a class. The following are examples of using reflection to operate related methods and properties of a class:

1. Creating objects using reflection

Using reflection to dynamically create an object of a class, the following is the implementation code ：

Class clazz = Class.forName("java.lang.String");
Constructor constructor = clazz.getDeclaredConstructor(String.class);
String str = (String) constructor.newInstance("Hello, World!");

2. Use reflection to call the method of the class

You can use reflection to dynamically call the method of the class. The following is the implementation code:

Class clazz = Class.forName("java.lang.String");
Method method = clazz.getDeclaredMethod("charAt", int.class);
char c = (char) method.invoke("Hello, World!", 1);

3. Use reflection to read and modify the attributes of a class

Use reflection to dynamically read and modify the attributes of a class. The following is the implementation code:

Class clazz = Class.forName("java.lang.String");
Field field = clazz.getDeclaredField("value");
field.setAccessible(true); //设置私有属性可读写
String str = "Hello, World!";
char[] chars = (char[]) field.get(str);
chars[0] = 'h';
System.out.println(str); //输出: hello, World!

Summary

This article explains how to use the Reflection function in Java for reflection operations. The reflection mechanism is a very important technology in Java programming. It allows programmers to obtain and operate class information and properties at runtime, allowing programmers to dynamically create, access and modify objects, methods and properties of a class. After learning the reflection mechanism, we can write Java applications more flexibly and write scalable and versatile code.

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