每日代码 - 6/26 lambda表达式

时间 2019-11-05

标签每日代码 lambda 表达式繁體版

原文原文链接

public class CartViewRender {
    public static CartView renderMyCartView(Cart cart){
        ErrorCodeEnum errorCode = null;
        try {
            cart.source = CartSource.My_Cart;
            CartFlowProccess.proccessMyCart(cart);
        } catch (TradeBaseException e) {
            errorCode = e.getErrorCodeEnum();
        } catch(Exception e){
            errorCode = ErrorCodeEnum.Cart_Error_System;
        }
        return RenderViewHelper.renderMyCartView(cart, errorCode);
    }

    public static CartView renderMobileMyCartView(Cart cart){
        ErrorCodeEnum errorCode = null;
        try {
            CartFlowProccess.proccessMyCart(cart);
        } catch (TradeBaseException e) {
            errorCode = e.getErrorCodeEnum();
        } catch(Exception e){
            errorCode = ErrorCodeEnum.Cart_Error_System;
        }
        return RenderViewHelper.renderMyCartView(cart, errorCode);
    }

    public static CartView renderAddCartView(Cart cart){
        ErrorCodeEnum errorCode = null;
        try {
            cart.source = CartSource.Add_Cart;
            CartFlowProccess.proccessAddCart(cart);
        } catch (TradeBaseException e) {
            errorCode = e.getErrorCodeEnum();
        } catch(Exception e){
            errorCode = ErrorCodeEnum.Cart_Error_System;
        }
        return RenderViewHelper.renderAddCartView(cart, errorCode);
    }

    //...

}

这是一段典型的重复代码示例，前两个方法基本上是彻底重复的，最后一个方法则是很是的相似。先把前两个方法改了，这个很是简单。java

  public static CartView renderMyCartViewFromNoSource(Cart cart)
    {
        ErrorCodeEnum errorCode = null;
        try {
            CartFlowProccess.proccessMyCart(cart);
        } catch (TradeBaseException e) {
            errorCode = e.getErrorCodeEnum();
        } catch(Exception e){
            errorCode = ErrorCodeEnum.Cart_Error_System;
        }
        return RenderViewHelper.renderMyCartView(cart, errorCode);

    }
    public static CartView renderMyCartView(Cart cart){
        cart.source = CartSource.My_Cart;
        return renderMyCartViewFromNoSource(cart);
    }

    public static CartView renderMobileMyCartView(Cart cart){
       return renderMyCartViewFromNoSource(cart);
    }

比较麻烦的是最后一个方法如何消除重复，在.net的世界中有delegate和lambda表达式，这个问题会比较容易搞定，而java只能用匿名类了。ide

首先观察第三个方法与前两个方法的不一样之处。其实只有两行代码不一样，那么咱们只要想办法将它们抽取出来就能够了。spa

先声明两个泛型接口，用于表示两个变化点：.net

interface Action<T>
{
    void act(T t);
}

interface Func<T1,T2,T3>
{
    T3 execute(T1 t1,T2 t2);
}

而后使用这两个接口建立一个通用方法。code

 public static CartView renderCartView(Cart cart, Action<Cart> action, Func<Cart, ErrorCodeEnum, CartView> func)
    {
        ErrorCodeEnum errorCode = null;
        Action<Cart> cartAction = null;

        try
        {
            action.act(cart);
        } catch (TradeBaseException e)
        {
            errorCode = e.getErrorCodeEnum();
        } catch (Exception e)
        {
            errorCode = ErrorCodeEnum.Cart_Error_System;
        }
        return func.execute(cart, errorCode);
    }

最后改写最后一个方法的实现，因为没有lambda表达式，代码看上去比较复杂些。blog

 public static CartView renderAddCartView(Cart cart)
    {
        cart.source=CartSource.Add_Cart;

        return renderCartView(cart, new Action<Cart>()
                {
                    @Override
                    public void act(Cart cart)
                    {
                        CartFlowProccess.proccessAddCart(cart);
                    }
                }, new Func<Cart, ErrorCodeEnum, CartView>()
                {
                    @Override
                    public CartView execute(Cart cart, ErrorCodeEnum errorCode)
                    {
                        return RenderViewHelper.renderAddCartView(cart, errorCode);
                    }
                }
        );
    }

若是你用了Intellj IDE，它会帮你自动作一些代码格式化。Java8以后就能支持的更好了。接口

最后完整代码以下：get

public class CartViewRender
{


    public static CartView renderCartView(Cart cart, Action<Cart> action, Func<Cart, ErrorCodeEnum, CartView> func)
    {
        ErrorCodeEnum errorCode = null;
        Action<Cart> cartAction = null;

        try
        {
            action.act(cart);
        } catch (TradeBaseException e)
        {
            errorCode = e.getErrorCodeEnum();
        } catch (Exception e)
        {
            errorCode = ErrorCodeEnum.Cart_Error_System;
        }
        return func.execute(cart, errorCode);
    }


    public static CartView renderMyCartViewFromNoSource(Cart cart)
    {
        return renderCartView(cart, new Action<Cart>()
                {
                    @Override
                    public void act(Cart cart)
                    {
                        CartFlowProccess.proccessMyCart(cart);
                    }
                }, new Func<Cart, ErrorCodeEnum, CartView>()
                {
                    @Override
                    public CartView execute(Cart cart, ErrorCodeEnum errorCode)
                    {
                        return RenderViewHelper.renderMyCartView(cart, errorCode);
                    }
                }
        );
    }

    public static CartView renderMyCartView(Cart cart)
    {
        cart.source = CartSource.My_Cart;
        return renderMyCartViewFromNoSource(cart);
    }

    public static CartView renderMobileMyCartView(Cart cart)
    {
        return renderMyCartViewFromNoSource(cart);
    }

    public static CartView renderAddCartView(Cart cart)
    {
        cart.source=CartSource.Add_Cart;

        return renderCartView(cart, new Action<Cart>()
                {
                    @Override
                    public void act(Cart cart)
                    {
                        CartFlowProccess.proccessAddCart(cart);
                    }
                }, new Func<Cart, ErrorCodeEnum, CartView>()
                {
                    @Override
                    public CartView execute(Cart cart, ErrorCodeEnum errorCode)
                    {
                        return RenderViewHelper.renderAddCartView(cart, errorCode);
                    }
                }
        );
    }

    //...

}