#Lambda表達(dá)式
Lambda允許把函數(shù)作為一個方法的參數(shù)（函數(shù)作為參數(shù)傳遞進(jìn)方法中)
#lambda表達(dá)式本質(zhì)上就是一個匿名方法。比如下面的例子：
public int add(int x, int y) { return x y;}轉(zhuǎn)成Lambda表達(dá)式后是這個樣子：
(int x, int y) -> x y;參數(shù)類型也可以省略，Java編譯器會根據(jù)上下文推斷出來：
(x, y) -> x y; //返回兩數(shù)之和或者
(x, y) -> { return x y; } //顯式指明返回值#java 8 in Action這本書里面的描述：
A lambda expression can be understood as a concise representation of an anonymous functionthat can be passed around: it doesn’t have a name, but it has a list of parameters, a body, areturn type, and also possibly a list of exceptions that can be thrown. That’s one big definition;#格式：
(x, y) -> x y;-----------------(x,y)：參數(shù)列表x y : body#Lambda表達(dá)式用法實(shí)例：
package LambdaUse;/** * @author zhangwenlong * @date 2019/8/25 15:17 */public class LambdaUse { public static void main(String[] args) { //匿名類實(shí)現(xiàn) Runnable r1 = new Runnable() { @Override public void run() { System.out.println("Hello world"); } }; //Lambda方式實(shí)現(xiàn) Runnable r2 = ()-> System.out.println("Hello world"); process(r1); process(r2); process(()-> System.out.println("Hello world")); } private static void process(Runnable r){ r.run(); }}輸出的結(jié)果：
Hello worldHello worldHello worldFunctionalInterface注解修飾的函數(shù)
#predicate的用法
package LambdaUse;import java.applet.Applet;import java.util.ArrayList;import java.util.Arrays;import java.util.List;import java.util.function.LongPredicate;import java.util.function.Predicate;/** * @author zhangwenlong * @date 2019/8/25 15:30 */public class PredicateTest { //通過名字（Predicate實(shí)現(xiàn)） private static List<Apple> filterApple(List<Apple> list, Predicate<Apple> predicate){ List<Apple> appleList = new ArrayList<>(); for(Apple apple : list){ if(predicate.test(apple)){ appleList.add(apple); } } return appleList; } //通過重量（LongPredicate實(shí)現(xiàn)） private static List<Apple> filterWeight(List<Apple> list, LongPredicate predicate){ List<Apple> appleList = new ArrayList<>(); for(Apple apple : list){ if(predicate.test(apple.getWeight())){ appleList.add(apple); } } return appleList; } public static void main(String[] args) { List<Apple> list = Arrays.asList(new Apple("蘋果",120),new Apple("香蕉",110)); List<Apple> applelist = filterApple(list,apple -> apple.getName().equals("蘋果")); System.out.println(applelist); List<Apple> appleList = filterWeight(list, (x) -> x > 110); System.out.println(appleList); }}執(zhí)行結(jié)果：
[Apple{name='蘋果', weight=120}][Apple{name='蘋果', weight=120}]#Lambda表達(dá)式的方法推導(dǎo)
package LambdaUse;import java.util.function.Consumer;/** * @author zhangwenlong * @date 2019/8/25 16:02 */public class MethodReference { private static <T> void useConsumer(Consumer<T> consumer,T t){ consumer.accept(t); } public static void main(String[] args) { //定義一個匿名類 Consumer<String> stringConsumer = (s) -> System.out.println(s); useConsumer(stringConsumer,"Hello World"); //lambda useConsumer((s) -> System.out.println(s),"ni hao"); //Lambda的方法推導(dǎo) useConsumer(System.out::println,"da jia hao"); }}執(zhí)行結(jié)果：
Hello Worldni haoda jia hao參數(shù)推導(dǎo)其他例子：
package LambdaUse;import java.net.Inet4Address;import java.util.function.BiFunction;import java.util.function.Function;/** * @author zhangwenlong * @date 2019/8/25 16:53 */public class paramterMethod { public static void main(String[] args) { //情況1：A method reference to a static method (for example, the method parseInt of Integer, written Integer::parseInt) //靜態(tài)方法 //常用的使用 Integer value = Integer.parseInt("123"); System.out.println(value); //使用方法推導(dǎo) Function<String,Integer> stringIntegerFunction = Integer::parseInt; Integer apply = stringIntegerFunction.apply("123"); System.out.println(apply); //情況2：A method reference to an instance method of an arbitrary type (for example, the method length of a String, written String::length) //對象的方法 String ss = "helloWorld"; System.out.println(ss.charAt(3)); //推導(dǎo)方法 BiFunction<String,Integer,Character> stringIntegerCharacterBiFunction = String::charAt; System.out.println(stringIntegerCharacterBiFunction.apply(ss,3)); //情況3：構(gòu)造函數(shù)方法推導(dǎo) //常用方式 Apple apple = new Apple("蘋果",120); System.out.println(apple); //推導(dǎo)方式 BiFunction<String,Integer,Apple> appleBiFunction = Apple::new; System.out.println(appleBiFunction.apply("蘋果",120)); }}執(zhí)行結(jié)果：
123123llApple{name='蘋果', weight=120}Apple{name='蘋果', weight=120}具體的詳細(xì)解釋可以參考：
#Stream（流以及一些常用的方法）
特點(diǎn)：并行處理
例子：
package StreamUse;import java.util.*;import java.util.stream.Collectors;/** * @author zhangwenlong * @date 2019/8/25 17:20 */public class StreamTest { public static void main(String[] args) { List<Apple> appleList = Arrays.asList( new Apple("蘋果",110), new Apple("桃子",120), new Apple("荔枝",130), new Apple("香蕉",140), new Apple("火龍果",150), new Apple("芒果",160) ); System.out.println(getNamesByCollection(appleList)); System.out.println(getNamesByStream(appleList)); } //collection實(shí)現(xiàn)查詢重量小于140的水果的名稱 private static List<String> getNamesByCollection(List<Apple> appleList){ List<Apple> apples = new ArrayList<>(); //查詢重量小于140的水果 for(Apple apple : appleList){ if(apple.getWeight() < 140){ apples.add(apple); } } //排序 Collections.sort(apples,(a,b)->Integer.compare(a.getWeight(),b.getWeight())); List<String> appleNamesList = new ArrayList<>(); for(Apple apple : apples){ appleNamesList.add(apple.getName()); } return appleNamesList; } //stream實(shí)現(xiàn)查詢重量小于140的水果的名稱 private static List<String> getNamesByStream(List<Apple> appleList){ return appleList.stream().filter(d ->d.getWeight() < 140) .sorted(Comparator.comparing(Apple::getWeight)) .map(Apple::getName) .collect(Collectors.toList()); }}