JAVA8 in Action:行為參數化,匿名類及lambda表達式的初步認知實例整理
阿新 • • 發佈:2018-10-26
例如 choose 集合 事先 inter color 蘋果 ant 模式
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:行為參數化,匿名類及lambda表達式的初步認知實例整理*****************************/ /**首先了解的幾個概念: * 1.行為參數化:就是一個方法接受多個不同的行為作為參數,並在內部是使用它們,完成不同行為的能力,是一種可以幫助你處理頻繁的需求變更的一種軟件開發模式; * 2.匿名類:與我們所熟悉的java局部類差不多,但是匿名類沒有名字,它允許你同事聲明並實例化一個類(隨用隨建); * 3.ambda表達式:由參數,箭頭和主體組成,如:(Apple a1,Apple a2) -> a1.getWeight().compareTo(a2.getWeight()); * ----lambda參數------ -箭頭- -------------lambda主體--------------- * */ //我們以實現從一個列表中篩選出綠蘋果作為例子: //1.基礎數據 //創建蘋果實體類 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.由淺入深的實例: //初級做法:僅僅只能用於選出綠色的蘋果 public static List<Apple> chooseGreenApple(List<Apple> apples){ List<Apple> result = new ArrayList<Apple>();//用於盛放篩選出來的綠蘋果的集合 for(Apple apple:apples){ if("green".equals(apple.getColor())){//選出綠蘋果放入到集合中 result.add(apple); } } return result; } //一級拓展:以顏色作為參數,可以根據參數選出想要的顏色的蘋果 public static List<Apple> choseAppleByColor(List<Apple> apples,String color){ List<Apple> result = new ArrayList<Apple>();//用於盛放篩選出來的綠蘋果的集合 for(Apple apple:apples){ if(color.equals(apple.getColor())){//根據參數選出所需要的蘋果放入到集合中 result.add(apple); } } return result; } //二級拓展,對多個屬性進行篩選(如顏色,重量) public static List<Apple> chooseApples(List<Apple> apples,String color, double weight,boolean flag){//謂詞flag用於區分根據顏色還是根據重量篩選 List<Apple> result = new ArrayList<Apple>();//用於盛放篩選出來的蘋果的集合 for(Apple apple:apples){ //根據flag確定使用以哪個參數為依據來選出所需要的蘋果放入到集合中 if((flag && color.equals(apple.getColor())) || (!flag && apple.getWeight() > weight)){ result.add(apple); } } return result; } //三級拓展,根據抽象條件進行篩選: //定義一個接口來對選擇標準建模: public interface ApplePredicate{ boolean test (Apple apple); } //以ApplePredicate的多個不同的實現來代表不同的選擇標準 //僅僅用來選出重的蘋果 public class AppleHeavy implements ApplePredicate{ public boolean test (Apple apple){ return apple.getWeight() > 180; } } //如果僅僅用來選出綠色的蘋果 public class AppleColor implements ApplePredicate{ public boolean test (Apple apple){ return "green".equals(apple.getColor()); } } //在利用ApplePredicte改過之後,該方法就變成了這個樣子, // 我們在使用的時候只需要創建不同個ApplePredicate對象,將他傳遞給chooseApples方法即可,大大的增加了他的靈活性 public static List<Apple> chooseApples(List<Apple> apples, ApplePredicate predicate){ List<Apple> result = new ArrayList<Apple>();//用於盛放篩選出來的蘋果的集合 for(Apple apple:apples){ if(predicate.test(apple)){ result.add(apple); } } return result; } //終極超級酷炫拓展,將List類型抽象化 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(){ //創建集合: List<Apple> appleList = Arrays.asList(new Apple("green",200),new Apple("red",150)); //初級做法:僅僅只能用於選出綠色的蘋果 List<Apple> greenApples__1 = chooseGreenApple(appleList); //一級拓展:以顏色作為參數,可以根據參數選出想要的顏色的蘋果 //例如篩選出紅蘋果: List<Apple> greenApples__2 = choseAppleByColor(appleList,"red"); //二級拓展,對多個屬性進行篩選(如顏色,重量) //例如篩選出紅蘋果: List<Apple> greenApples__13 = chooseApples(appleList,"red",0,true); //例如篩選出重蘋果: List<Apple> weightApples__1 = chooseApples(appleList,"",180,false); //三級拓展,根據抽象條件進行篩選: //例如篩選出綠蘋果: List<Apple> greenApples = chooseApples(appleList,new AppleColor()); //例如篩選出重蘋果: List<Apple> weightApples_1 = chooseApples(appleList,new AppleHeavy()); //四級拓展,使用匿名類同時聲明和實例化一個類:(可以讓你無需事先實例化,隨用隨建,提高效率) List<Apple> weightApples_2 = chooseApples(appleList, new ApplePredicate() { public boolean test(Apple apple) {return apple.getWeight() > 180;} }); //五級拓展,使用lambda表達式:(顯得更加幹凈整潔) //選出綠色的蘋果 List<Apple> weightApples_3 = chooseApples(appleList,(Apple apple) -> "green".equals(apple.getColor())); //終極超級酷炫拓展,將List類型抽象化: //類型抽象化後,你可以廣泛的推廣了,可以用在西瓜上,汽車上,Integer,String。。。。。。。。。。。。 //例如:篩選出集合中包含“e”的單詞集合: List<String> stringList = Arrays.asList("one","two","three","four"); List<String> include_e = chooseSomeThind(stringList,(String str)-> str.contains("e")); //例如:篩選出集合中大於5的數字的集合: 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!"); } }
轉自:https://blog.csdn.net/qq_37107280/article/details/77417500
JAVA8 in Action:行為參數化,匿名類及lambda表達式的初步認知實例整理