• 一、函数式编程


    函数编程演化历程

    1. 将业务代码直接写死代码里
    2. 将单一维度的条件作为参数传入方法中,方法内根据参数进行业务逻辑实现。
    3. 将多个维度的条件作为参数传入方法中,业务实现需要根据不同的参数处理不同的逻辑。
    4. 将业务逻辑封装为一个实体类,方法接受实体类为参数,方法内部调用实体类的处理逻辑。
    5. 调用方法时不再创建实体类,而是使用匿名函数的形式替代。
    6. 使用Lambda表达式替代匿名函数的形式,作为方法的参数,真正实现判断逻辑参数化传递。

    案例

    目的:针对不同需求对购物车的的商品进行过滤筛选

    准备

    1. 商品对象
      @Data
      @NoArgsConstructor
      @AllArgsConstructor
      public class Goods {
          // 编号
          private Integer goodId;
          // 商品名称
          private String goodName;
          // 商品类型
          private Enum goodType;
          // 单价
          private Double goodPrice;
          // 总价
          private Double goodTotalPrice;
          // 数量
          private Integer totalNum;
      }
      
    2. 商品枚举类
    /**
     * 商品类型的枚举类
     */
    public enum GoodTypeEnum {
        APPAREL(10,"服装类"),
        DIGITAL(20,"数码类"),
        BOOKS(30,"图书类"),
        SPORTS(40,"运动类");
        // 商品类型的编号
        private Integer code;
        // 商品类型的名称
        private String name;
    
        /**
         * 构造函数
         * @param code
         * @param name
         */
        GoodTypeEnum(Integer code, String name) {
            this.code = code;
            this.name = name;
        }
    }    
    
    1. 模拟商品数据
      /**
       * 模拟商品数据
       */
      private static List<Goods> goodsList= new ArrayList<Goods>(){
          {
              add(new Goods(111,"无人机", GoodTypeEnum.DIGITAL,10000.00, 10000.00,1));
              add(new Goods(112,"VR一体机", GoodTypeEnum.DIGITAL,13000.00, 13000.00,1));
              add(new Goods(113,"衬衫", GoodTypeEnum.APPAREL,100.00, 300.00,3));
              add(new Goods(114,"牛仔裤", GoodTypeEnum.APPAREL,120.00, 120.00,1));
              add(new Goods(115,"Java编程思想", GoodTypeEnum.BOOKS,80.00, 80.00,1));
              add(new Goods(116,"Java核心技术", GoodTypeEnum.BOOKS,90.00, 90.00,1));
              add(new Goods(117,"算法", GoodTypeEnum.BOOKS,60.00, 60.00,1));
              add(new Goods(118,"跑步机", GoodTypeEnum.SPORTS,3600.00, 3600.00,1));
      
          }
      };
      
      /**
       * 获取商品列表
       * @return
       */
      public  List<Goods> getGoodsList(){
          return goodsList;
      }
      

    实现

    Version 1.0.0

        /**
         * Version 1.0.0
         * 找出购物车中所有数码类产品
         * @param goodsList
         * @return
         */
        public  List<Goods> filterGoodsList(List<Goods> goodsList){
            List<Goods> result = new ArrayList<>();
            for (Goods goods : goodsList) {
                if (GoodTypeEnum.DIGITAL.equals(goods.getGoodType())){
                    result.add(goods);
                }
            }
            return result;
        }
    

    测试

        @Test
        public void version1(){
            GoodsService goodsService = new GoodsService();
            List<Goods> goodsList = goodsService.getGoodsList();
            List<Goods> goods = goodsService.filterGoodsList(goodsList);
            System.out.println(JSON.toJSONString(goods,true));
    
        }
    

    Version 2.0.0

        /**
         * 根据类型找出购物车中对应类型的产品
         * @param goodsList
         * @return
         */
        public  List<Goods> filterGoodsList(List<Goods> goodsList,GoodTypeEnum goodType){
            List<Goods> result = new ArrayList<>();
            for (Goods goods : goodsList) {
                if (goodType.equals(goods.getGoodType())){
                    result.add(goods);
                }
            }
            return result;
        }
    

    测试

        @Test
        public void version2(){
            GoodsService goodsService = new GoodsService();
            List<Goods> goodsList = goodsService.getGoodsList();
            List<Goods> goods = goodsService.filterGoodsList(goodsList, GoodTypeEnum.SPORTS);
            System.out.println(JSON.toJSONString(goods,true));
    
        }
    

    Version 3.0.0

        /**
         * 支持通过商品类型或者总价来过滤商品
         * @param goodsList
         * @param goodType
         * @param totalPrice
         * @param goodTypeOrPrice - true:根据商品类型 false:根据商品总价
         * @return
         */
        public  List<Goods> filterGoodsList(List<Goods> goodsList,GoodTypeEnum goodType,Double totalPrice,boolean goodTypeOrPrice){
            List<Goods> result = new ArrayList<>();
            for (Goods goods : goodsList) {
                //goodTypeOrPrice - true:根据商品类型 false:根据商品总价
                if (goodTypeOrPrice && goodType.equals(goods.getGoodType())||
                        !goodTypeOrPrice && goods.getGoodTotalPrice()>totalPrice
                ){
                    result.add(goods);
                }
            }
            return result;
        }
    

    测试

        @Test
        public void version3(){
            GoodsService goodsService = new GoodsService();
            List<Goods> goodsList = goodsService.getGoodsList();
            List<Goods> goods = goodsService.filterGoodsList(goodsList, GoodTypeEnum.SPORTS,1000.00,false);
            System.out.println(JSON.toJSONString(goods,true));
    
        }
    

    Version 4.0.0

        /**
         * 根据不同的goods判断标准,对商品列表进行过滤
         * @param goodsList
         * @param goodsPredicate(或者Predicate接口) - 不同的商品判断标准
         * @return
         */
        public  List<Goods> filterGoodsList(List<Goods> goodsList,GoodsPredicate goodsPredicate){
            List<Goods> result = new ArrayList<>();
            for (Goods goods : goodsList) {
                if (goodsPredicate.test(goods)){
                    result.add(goods);
                }
            }
            return result;
        }
    
        /**
         * Goods判断标准策略接口
         */
        public interface GoodsPredicate {
            /**
             * 选择判断标准
             * @param goods
             * @return
             */
            boolean test(Goods goods);
        }
    
        /**
         * Goods商品类型为图书类型的判断标准
         */
        public class  BooksGoodsPredicate implements GoodsPredicate {
        
            @Override
            public boolean test(Goods goods) {
                return GoodTypeEnum.BOOKS.equals(goods.getGoodType());
            }
        }
    

    测试

        @Test
        public void version4(){
            GoodsService goodsService = new GoodsService();
            List<Goods> goodsList = goodsService.getGoodsList();
            List<Goods> goods = goodsService.filterGoodsList(goodsList,new BooksGoodsPredicate());
            System.out.println(JSON.toJSONString(goods,true));
    
        }
    

    Version 5.0.0

    考虑到判断标准多样化,没必要为标准写一个类,可以使用匿名内部类根据情况直接判断

        @Test
        public void version5(){
            GoodsService goodsService = new GoodsService();
            List<Goods> goodsList = goodsService.getGoodsList();
            List<Goods> goods = goodsService.filterGoodsList(goodsList,new GoodsPredicate(){
                @Override
                public boolean test(Goods goods){
                    return goods.getGoodTotalPrice()>5000;
                }
            });
            System.out.println(JSON.toJSONString(goods,true));
    
        }
    

    Version 6.0.0

    还可以进一步优化,使用lambda表达式

        @Test
        public void version6(){
            GoodsService goodsService = new GoodsService();
            List<Goods> goodsList = goodsService.getGoodsList();
            List<Goods> goods = goodsService.filterGoodsList(goodsList,(Goods good) -> good.getGoodTotalPrice()>10000);
            System.out.println(JSON.toJSONString(goods,true));
    
        }
    
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  • 原文地址:https://www.cnblogs.com/bigfairy/p/14002040.html
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