An in-depth analysis of three methods of Java reflection

Java Reflection: Exploring Three Methods

Introduction:
In Java development, reflection is a powerful feature that allows us to dynamically Obtain class information and operate on them. Through reflection, we can achieve many powerful functions, such as generating objects at runtime, calling class methods, accessing and modifying class properties, etc. This article will introduce three common reflection methods in Java and provide specific code examples.

1. Class object acquisition
In Java, each class will be compiled into a .class file, which contains metadata information of the class. We can obtain these metadata through the Class class to implement reflection operations on the class.

Sample code:

// 方法一：通过类名获取Class对象
Class<?> cls1 = MyClass.class;

// 方法二：通过实例对象获取Class对象
MyClass obj = new MyClass();
Class<?> cls2 = obj.getClass();

// 方法三：通过完整类名获取Class对象
String className = "com.example.MyClass";
try {
    Class<?> cls3 = Class.forName(className);
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}

2. Instantiate objects
Through reflection, we can dynamically instantiate an object of a class at runtime. Through the newInstance() method of the Class class, we can easily implement this function.

Sample code:

// 创建Class对象
Class<?> cls = MyClass.class;
// 实例化对象
try {
    Object obj = cls.newInstance();
    System.out.println(obj.getClass().getName());
} catch (InstantiationException | IllegalAccessException e) {
    e.printStackTrace();
}

3. Calling methods
Reflection can also be used to call methods of classes. Through the getMethod() method of the Class class, we can obtain the methods in the class and call them through the invoke() method.

Sample code:

// 创建Class对象
Class<?> cls = MyClass.class;
try {
    // 获取方法
    Method method = cls.getMethod("myMethod", String.class);
    // 创建实例对象
    Object obj = cls.newInstance();
    // 调用方法
    method.invoke(obj, "Hello, Reflection!");
} catch (NoSuchMethodException | IllegalAccessException | InstantiationException | InvocationTargetException e) {
    e.printStackTrace();
}

4. Accessing and modifying attributes
Reflection can also be used to access and modify attributes of a class. Through the getField() and getDeclaredField() methods of the Class class, we can obtain the attributes of the class and access and modify their values ​​through the set() and get() methods.

Sample code:

// 创建Class对象
Class<?> cls = MyClass.class;
try {
    // 获取属性
    Field field = cls.getDeclaredField("myField");
    // 创建实例对象
    Object obj = cls.newInstance();
    // 设置属性值
    field.set(obj, "Reflection");
    // 获取属性值
    System.out.println(field.get(obj));
} catch (NoSuchFieldException | IllegalAccessException | InstantiationException e) {
    e.printStackTrace();
}

Conclusion:
Through Java's reflection mechanism, we can dynamically obtain class information and operate them at runtime, which greatly enhances the flexibility of the program. and scalability. However, it should be noted that you should be careful when using reflection, because reflection operations will reduce the performance of the program and may produce some uncontrolled side effects. Therefore, reflection should be used with caution in actual development and avoid overuse.

Reference materials:
1. "Detailed explanation and practice of Java reflection mechanism": https://blog.csdn.net/xiaoxiaoyu510/article/details/89621550
2. "Basic of Java reflection mechanism" Introduction》: https://www.runoob.com/w3cnote/java-reflection-intro.html

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