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JAVA8 in Action:行为参数化,匿名类及lambda表达式的初步认知实例整理

时间:2018-10-25 22:11:59      阅读:272      评论:0      收藏:0      [点我收藏+]

标签:get   完美   酷炫   整理   gre   static   数据   声明   初步   

 
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;
 
/**
 * Created by Administrator on 2017/8/19 0013.
 */
public class Test {
 /*************************************JAVA8 in Action:行为参数化,匿名类及lambda表达式的初步认知实例整理*****************************/
 /**首先了解的几个概念:
  *     1.行为参数化:就是一个方法接受多个不同的行为作为参数,并在内部是使用它们,完成不同行为的能力,是一种可以帮助你处理频繁的需求变更的一种软件开发模式;
  *     2.匿名类:与我们所熟悉的java局部类差不多,但是匿名类没有名字,它允许你同事声明并实例化一个类(随用随建);
  *     3.ambda表达式:由参数,箭头和主体组成,如:(Apple a1,Apple a2)   ->    a1.getWeight().compareTo(a2.getWeight());
  *                                               ----lambda参数------  -箭头-  -------------lambda主体---------------
  * */
  //我们以实现从一个列表中筛选出绿苹果作为例子:
    //1.基础数据
    //创建苹果实体类
    class Apple{
        private String color;
        private double weight;
        public String getColor() {
            return color;
        }
        public void setColor(String color) {
            this.color = color;
        }
        public double getWeight() {
            return weight;
        }
        public void setWeight(double weight) {
            this.weight = weight;
        }
 
        public Apple(String color, double weight) {
            this.color = color;
            this.weight = weight;
        }
    }
    //2.由浅入深的实例:
    //初级做法:仅仅只能用于选出绿色的苹果
        public static List<Apple> chooseGreenApple(List<Apple> apples){
            List<Apple> result = new ArrayList<Apple>();//用于盛放筛选出来的绿苹果的集合
            for(Apple apple:apples){
                if("green".equals(apple.getColor())){//选出绿苹果放入到集合中
                    result.add(apple);
                }
            }
            return result;
        }
  //一级拓展:以颜色作为参数,可以根据参数选出想要的颜色的苹果
      public static List<Apple> choseAppleByColor(List<Apple> apples,String color){
          List<Apple> result = new ArrayList<Apple>();//用于盛放筛选出来的绿苹果的集合
          for(Apple apple:apples){
              if(color.equals(apple.getColor())){//根据参数选出所需要的苹果放入到集合中
                  result.add(apple);
              }
          }
            return result;
      }
  //二级拓展,对多个属性进行筛选(如颜色,重量)
        public static List<Apple> chooseApples(List<Apple> apples,String color, double weight,boolean flag){//谓词flag用于区分根据颜色还是根据重量筛选
            List<Apple> result = new ArrayList<Apple>();//用于盛放筛选出来的苹果的集合
            for(Apple apple:apples){
                //根据flag确定使用以哪个参数为依据来选出所需要的苹果放入到集合中
                if((flag && color.equals(apple.getColor())) || (!flag && apple.getWeight() > weight)){
                    result.add(apple);
                }
            }
            return result;
        }
    //三级拓展,根据抽象条件进行筛选:
        //定义一个接口来对选择标准建模:
        public interface  ApplePredicate{
            boolean test (Apple apple);
        }
        //以ApplePredicate的多个不同的实现来代表不同的选择标准
        //仅仅用来选出重的苹果
        public class AppleHeavy implements  ApplePredicate{
           public boolean test (Apple apple){
               return apple.getWeight() > 180;
           }
        }
        //如果仅仅用来选出绿色的苹果
        public class AppleColor implements  ApplePredicate{
            public boolean test (Apple apple){
                return "green".equals(apple.getColor());
            }
        }
        //在利用ApplePredicte改过之后,该方法就变成了这个样子,
        // 我们在使用的时候只需要创建不同个ApplePredicate对象,将他传递给chooseApples方法即可,大大的增加了他的灵活性
        public static List<Apple> chooseApples(List<Apple> apples, ApplePredicate predicate){
            List<Apple> result = new ArrayList<Apple>();//用于盛放筛选出来的苹果的集合
            for(Apple apple:apples){
                if(predicate.test(apple)){
                    result.add(apple);
                }
            }
            return result;
        }
    //终极超级酷炫拓展,将List类型抽象化
        public interface  predicatre<T>{
            boolean test(T t);
        }
         public static <T> List<T> chooseSomeThind(List<T> list, Predicate<T> p){
             List<T> result = new ArrayList<T>();
             for(T e:list){
                 if(p.test(e)){
                     result.add(e);
                 }
             }
            return result;
         }
    @org.junit.Test
    public void testChooseAppleByWhatYouWant(){
        //创建集合:
        List<Apple> appleList = Arrays.asList(new Apple("green",200),new Apple("red",150));
        //初级做法:仅仅只能用于选出绿色的苹果
            List<Apple> greenApples__1 = chooseGreenApple(appleList);
        //一级拓展:以颜色作为参数,可以根据参数选出想要的颜色的苹果
            //例如筛选出红苹果:
            List<Apple> greenApples__2 = choseAppleByColor(appleList,"red");
        //二级拓展,对多个属性进行筛选(如颜色,重量)
            //例如筛选出红苹果:
            List<Apple> greenApples__13 = chooseApples(appleList,"red",0,true);
            //例如筛选出重苹果:
            List<Apple> weightApples__1 = chooseApples(appleList,"",180,false);
        //三级拓展,根据抽象条件进行筛选:
            //例如筛选出绿苹果:
            List<Apple> greenApples = chooseApples(appleList,new AppleColor());
            //例如筛选出重苹果:
            List<Apple> weightApples_1 = chooseApples(appleList,new AppleHeavy());
        //四级拓展,使用匿名类同时声明和实例化一个类:(可以让你无需事先实例化,随用随建,提高效率)
            List<Apple> weightApples_2 = chooseApples(appleList, new ApplePredicate() {
                public boolean test(Apple apple) {return apple.getWeight() > 180;}
            });
        //五级拓展,使用lambda表达式:(显得更加干净整洁)
        //选出绿色的苹果
           List<Apple> weightApples_3 = chooseApples(appleList,(Apple apple) -> "green".equals(apple.getColor()));
        //终极超级酷炫拓展,将List类型抽象化:
            //类型抽象化后,你可以广泛的推广了,可以用在西瓜上,汽车上,Integer,String。。。。。。。。。。。。
             //例如:筛选出集合中包含“e”的单词集合:
             List<String> stringList = Arrays.asList("one","two","three","four");
             List<String> include_e = chooseSomeThind(stringList,(String str)-> str.contains("e"));
            //例如:筛选出集合中大于5的数字的集合:
            List<Integer> integersList = Arrays.asList(1,2,3,4,5,6,7,8,10);
            List<Integer> bigerThan_5 = chooseSomeThind(integersList,(Integer a)-> a>5);
            System.out.print("非常完美!");
    }
 
}

转自:https://blog.csdn.net/qq_37107280/article/details/77417500

JAVA8 in Action:行为参数化,匿名类及lambda表达式的初步认知实例整理

标签:get   完美   酷炫   整理   gre   static   数据   声明   初步   

原文地址:https://www.cnblogs.com/shundong106/p/9853126.html

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