public interface Num {
  void show();
  
  int getNum();
  
  int getProduct(int x);
}

public class MyNum implements Num {
  @Override
  public int getNum() {
    return 3;
  }
  
  @Override
  public int getProduct(int x) {
    return x;
  }

  @Override
  public void show() {
    System.out.println("底层方法打印数字99");
  }
}

public class NumProxy {
  private Object num;

　　//通过构造方法构造接口的实现类对象
  public NumProxy(Object num) {
    this.num = num;
  }

  public Object getNumByProxy(){
    Object numProxy = Proxy.newProxyInstance(num.getClass().getClassLoader(), new Class[]{Num.class}, new InvocationHandler() {
      /**
       * method: 对应于在代理实例上调用的接口方法的 Method 实例。我理解的就是被代理的真实方法实例
       * args: 我理解的是真实方法的参数数组
       */
      @Override
      public Object invoke(Object proxy, Method method, Object[] args)
          throws Throwable {
        Object obj = null;
        System.out.println("在方法之前开始记录");
        String methodName = method.getName();
        if("getProduct".equals(methodName)){
          obj = method.invoke(num, args);
          obj = (Integer) obj * 2;
          System.out.println("proxy: getProduct()结束");
        }
        else if("show".equals(methodName)){
          obj = method.invoke(num, args);
          System.out.println("proxy: show()结束");
        }
        return obj;
      }
    });
    return numProxy;
  }
}

public class NumProxyImpl implements InvocationHandler {
　　//这里我把接口类型具体化了, 没有写成Object
  private Num num;
  
  public NumProxyImpl(Num num){
    this.num = num;
  }
  
  @Override
  public Object invoke(Object proxy, Method method, Object[] args)
      throws Throwable {
    Object obj = null;
    String methodName = method.getName();
    if("getProduct".equals(methodName)){
      System.out.println("proxy: getProduct()开始");
      obj = method.invoke(num, args);
      obj = (Integer) obj * 2;
      System.out.println("proxy: getProduct()结束");
    }else if("show".equals(methodName)){
      System.out.println("proxy: show()开始");
      obj = method.invoke(num, args);
      System.out.println("proxy: show()结束");
    }
    return obj;
  }
}

public class TestNum {
  public static void main(String[] args) {
　　　　//两种方式一起测试
    NumProxy np = new NumProxy(new MyNum());
    Num numProxy = (Num) np.getNumByProxy();
    int x = numProxy.getProduct(2);
    System.out.println(x);
    numProxy.show();
    
    System.out.println("----------------");
    NumProxyImpl npi = new NumProxyImpl(new MyNum());
    Num numPro = (Num) Proxy.newProxyInstance(Num.class.getClassLoader(), new Class[]{Num.class}, npi);
    int n = numPro.getProduct(3);
    System.out.println(n);
    numPro.show();
  }
}