Java 世界的法外狂徒：反射

import java.lang.reflect.Method;

public class ReflectionExample {
    public static void main(String[] args) {
        // 假设在运行时需要调用某个类的方法，但该类在编译时未知
        String className = "com.example.MyClass";

        try {
            // 使用反射动态加载类
            Class<?> clazz = Class.forName(className);

            // 使用反射获取指定方法
            Method method = clazz.getMethod("myMethod");

            // 使用反射创建对象
            Object obj = clazz.newInstance();

            // 使用反射调用方法
            method.invoke(obj);

        } catch (ClassNotFoundException e) {
            System.out.println("类未找到：" + className);
        } catch (NoSuchMethodException e) {
            System.out.println("方法未找到");
        } catch (IllegalAccessException | InstantiationException e) {
            System.out.println("无法实例化对象");
        } catch (Exception e) {
            System.out.println("其他异常：" + e.getMessage());
        }
    }
}

// 使用类名获取
Class<?> clazz = Class.forName("com.example.MyClass");

// 使用类字面常量获取
Class<?> clazz = MyClass.class;

// 使用对象的 getClass() 方法获取
MyClass obj = new MyClass();
Class<?> clazz = obj.getClass();

String className = clazz.getName(); // 获取类的全限定名
int modifiers = clazz.getModifiers(); // 获取类的修饰符，如 public、abstract 等
Class<?> superClass = clazz.getSuperclass(); // 获取类的直接父类
Class<?> superClass = clazz.getSuperclass(); // 获取类的直接父类
Class<?>[] interfaces = clazz.getInterfaces(); // 获取类实现的接口数组
Constructor<?>[] constructors = clazz.getConstructors(); // 获取类的公共构造函数数组
Method[] methods = clazz.getMethods(); // 获取类的公共方法数组
Field[] fields = clazz.getFields(); // 获取类的公共字段数组
Object obj = clazz.newInstance(); // 创建类的实例，相当于调用无参构造函数

if (obj instanceof MyClass) {
    MyClass myObj = (MyClass) obj;
    // 执行针对 MyClass 类型的操作
}

if (animal instanceof Dog) {
    Dog dog = (Dog) animal;
    dog.bark();
} else if (animal instanceof Cat) {
    Cat cat = (Cat) animal;
    cat.meow();
}

if (obj instanceof MyInterface) {
    MyInterface myObj = (MyInterface) obj;
    myObj.doSomething();
}

if (obj instanceof MyBaseClass) {
    MyBaseClass myObj = (MyBaseClass) obj;
    // 执行 MyBaseClass 类型的操作
}

Class<?> clazz = MyClass.class;
boolean result = clazz.isInstance(obj);

// 定义抽象对象接口
interface Image {
    void display();
}

// 定义原始对象
class RealImage implements Image {
    private String fileName;

    public RealImage(String fileName) {
        this.fileName = fileName;
        loadFromDisk();
    }

    private void loadFromDisk() {
        System.out.println("Loading image:" + fileName);
    }

    @Override
    public void display() {
        System.out.println("Displaying image:" + fileName);
    }
}

// 定义代理对象
class ImageProxy implements Image {
    private String filename;
    private RealImage realImage;

    public ImageProxy(String filename) {
        this.filename = filename;
    }

    @Override
    public void display() {
        if (realImage == null) {
            realImage = new RealImage(filename);
        }
        realImage.display();
    }
}

public class ProxyPatternExample {
    public static void main(String[] args) {
        // 使用代理对象访问实际对象
        Image image = new ImageProxy("test_10mb.jpg");
        // 第一次访问，加载实际对象
        image.display();
        // 第二次访问，直接使用已加载的实际对象
        image.display();
    }
}

Loading image:test_10mb.jpg
Displaying image:test_10mb.jpg
Displaying image:test_10mb.jpg

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

// 定义抽象对象接口
interface Image {
    void display();
}

// 定义原始对象
class RealImage implements Image {
    private String filename;

    public RealImage(String filename) {
        this.filename = filename;
        loadFromDisk();
    }

    private void loadFromDisk() {
        System.out.println("Loading image: " + filename);
    }

    public void display() {
        System.out.println("Displaying image: " + filename);
    }
}

// 实现 InvocationHandler 接口的代理处理类
class ImageProxyHandler implements InvocationHandler {

    private Object realObject;

    public ImageProxyHandler(Object realObject) {
        this.realObject = realObject;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        Object result = null;
        if (method.getName().equals("display")) {
            System.out.println("Proxy: before display");
            result = method.invoke(realObject, args);
            System.out.println("Proxy: after display");
        }
        return result;
    }
}

public class DynamicProxyExample {

    public static void main(String[] args) {
        // 创建原始对象
        Image realImage = new RealImage("image.jpg");
        // 创建动态代理对象
        Image proxyImage = (Image) Proxy.newProxyInstance(Image.class.getClassLoader(), new Class[]{Image.class}, new ImageProxyHandler(realImage));
        // 使用代理对象访问实际对象
        proxyImage.display();
    }
}

Loading image: image.jpg
Proxy: before display
Displaying image: image.jpg
Proxy: after display

import java.lang.reflect.Field;

class MyClass {
    private String privateField = "Private Field Value";
}

public class ReflectionExample {

    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
        MyClass myObj = new MyClass();
        // 获取私有字段对象
        Field privateField = MyClass.class.getDeclaredField("privateField");

        // 取消对私有字段的访问限制
        privateField.setAccessible(true);

        // 获取私有字段的值
        String fieldValue = (String) privateField.get(myObj);
        System.out.println("Original value of privateField: " + fieldValue);

        // 修改私有字段的值
        privateField.set(myObj, "New Field Value");

        // 再次获取私有字段的值
        fieldValue = (String) privateField.get(myObj);
        System.out.println("Modified value of privateField: " + fieldValue);
    }
}

Original value of privateField: Private Field Value
Modified value of privateField: New Field Value