【Java核心技术】类型信息(Class对象 反射 动态代理)

public class Base {
    static int num = 1;
 
    static {
        System.out.println("Base " + num);
    }
}
public class Main {
    public static void main(String[] args) {
        // 不会初始化静态块
        Class clazz1 = Base.class;
        System.out.println("------");
        // 会初始化
        Class clazz2 = Class.forName("zzz.Base");
    }
}

class Base { }
class Derived extends Base { }
 
public class Main {
    public static void main(String[] args) {
       Base base = new Derived();
       if (base instanceof Derived) {
           // 这里可以向下转换了
           System.out.println("ok");
       }
       else {
           System.out.println("not ok");
       }
    }
}

class Base { }
class Derived extends Base { }
 
public class Main {
    public static void main(String[] args) {
       Base base = new Derived();
       if (base instanceof Derived) {
           // 这里可以向下转换了
           System.out.println("ok");
       }
       else {
           System.out.println("not ok");
       }
    }
}

public interface Hello {
    void doSomething();
}
 
public class HelloImpl implements Hello {
    @Override
    public void doSomething() {
        System.out.println("HelloImpl doSomething");
    }
}
 
/**
 * 代理类
 */
public class ProxyHandler implements InvocationHandler {
    private Object proxyed;
 
    public ProxyHandler(Object proxy) {
        proxyed = proxy;
    }
 
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws InvocationTargetException, IllegalAccessException {
        System.out.println("proxy working");
        return method.invoke(proxyed, args);
    }
}
 
public static void main(String[] args) {
    Hello hello = new HelloImpl();
    Hello proxy = (Hello) Proxy.newProxyInstance(Hello.class.getClassLoader(),
            new Class[]{Hello.class}, new ProxyHandler(hello));
 
    proxy.doSomething();
}