Lambda表达式的使用

从苹果筛选的实现过程来一步一步的熟悉Java8语法

package top.hengshare.interviewer.java8.lambda; import com.google.common.collect.Lists; import lombok.Data; import java.util.ArrayList; import java.util.Collection; import java.util.Comparator; import java.util.List; import java.util.function.Predicate; import static com.google.common.collect.Collections2.filter; /** * @author StivenYang * @program interview * @description 这是一个苹果Apple * @date 2019-06-28 10:20 **/ @Data public class Apple { public Apple(String color) { this.color = color; } private String color; private double weight; public static List<Apple> filterGreenApples(List<Apple> inventory) { List<Apple> result = new ArrayList<Apple>(); for(Apple apple: inventory){ if( "green".equals(apple.getColor()) ){ result.add(apple); } } return result; } public static boolean isGreenApple(Apple apple) { return "green".equals(apple.getColor()); } static List<Apple> filterApples(List<Apple> inventory, Predicate<Apple> p) { ArrayList<Apple> result = Lists.newArrayList(); for (Apple apple : inventory) { if (p.test(apple)) { result.add(apple); } } return result; } public static List<Apple> filterApplesByColor(List<Apple> inventory, String color) { List<Apple> result = new ArrayList<Apple>(); for (Apple apple: inventory){ if ( apple.getColor().equals(color) ) { result.add(apple); } } return result; } public static List<Apple> filterApples(List<Apple> inventory, String color, double weight, boolean flag) { List<Apple> result = new ArrayList<Apple>(); for (Apple apple: inventory){ if ( (flag && apple.getColor().equals(color)) || (!flag && apple.getWeight() > weight) ){ result.add(apple); } } return result; } public static void main(String[] args) { List<Apple> appleList = Lists.newArrayList(); Apple green = new Apple("green"); green.setWeight(2D); appleList.add(green); Apple red = new Apple("red"); red.setWeight(3D); appleList.add(red); System.out.println(appleList); //第一次尝试：直接自定义函数，筛选绿色苹果 List<Apple> list1 = Apple.filterGreenApples(appleList); System.out.println(list1); //第二次尝试：定义函数，传入苹果的颜色 List<Apple> list2 = Apple.filterApplesByColor(appleList, "green"); System.out.println(list2); //第三次尝试：定义函数，传入重量作为参数 List<Apple> list3 = Apple.filterApplesByWeight(list2, 2D); System.out.println(list3); //第四次尝试：定义函数，同时传入重量和颜色作为参数,另加一个boolean对参数进行筛选 List<Apple> list4 = Apple.filterApples(appleList, "green", 2D, false); System.out.println(list4); //第五次尝试: 使用自定义的filterApples,第二个参数为谓词，通过谓词来对列表中的内容进行筛选 List<Apple> apples = Apple.filterApples(appleList, Apple::isGreenApple); System.out.println(apples); //第六次尝试：使用lambda表达式，简化我们上面的代码，让它更加容易阅读（但是有一个缺点是，需要自己定义一个filterApples函数 List<Apple> list6 = Apple.filterApples(appleList, (Apple apple) -> "red".equals(apple.getColor())); System.out.println(list6); //第七次尝试：使用lambda表达式，并且使用google提供的filter工具 Collection<Apple> list7 = filter(appleList, (Apple apple) -> "red".equals(apple.getColor())); System.out.println(list7); //对list进行排序 appleList.sort(new Comparator<Apple>() { @Override public int compare(Apple o1, Apple o2) { return o1.getColor().compareTo(o2.getColor()); } }); System.out.println(appleList); //使用lambda表达式对list进行排序 appleList.sort((Apple a1, Apple a2) -> a2.getColor().compareTo(a1.getColor())); System.out.println(appleList); } public static List<Apple> filterApplesByWeight(List<Apple> inventory, double weight) { List<Apple> result = new ArrayList<Apple>(); for (Apple apple: inventory){ if ( apple.getWeight() > weight ){ result.add(apple); } } return result; } }