Java番外篇2——jdk8新特性

1、Lambda

1.1、無參無返回值

public class Test {interface Print{void print();}public static void main(String[] args) { // Print print=new Print() { // @Override // public void print() { // System.out.println("hello word!"); // } // };Print print=()-> System.out.println("hello word!");print.print();} }

1.2、一個(gè)參數(shù)無返回值

public class Test {interface Print{void print(String str);}public static void main(String[] args) { // Print print=new Print() { // @Override // public void print(String str) { // System.out.println("hello word! "+str); // } // };Print print=str-> System.out.println("hello word! "+str);print.print("ruoye");} }

1.3、多個(gè)參數(shù)無返回值

public class Test {interface Print{void print(String str,String str1);}public static void main(String[] args) { // Print print=new Print() { // @Override // public void print(String str,String str1); { // System.out.println("hello word! "+str+str1); // } // };Print print=(str,str1)-> System.out.println("hello word! "+str+str1);print.print("ruoye","yoya");} }

1.4、多個(gè)參數(shù)有返回值(單句)

public class Test {interface Print{String print(String str,String str1);}public static void main(String[] args) {Print print=(str,str1)-> str+str1;System.out.println(print.print("ruoye", "yoya"));} }

1.4、多個(gè)參數(shù)有返回值(多句)

public class Test {interface Print{String print(String str,String str1);}public static void main(String[] args) {Print print=(str,str1)-> {System.out.println("hello word! "+str+str1);return str+str1;};System.out.println(print.print("ruoye", "yoya"));} }

2、函數(shù)式接口（@FunctionalInterface）

• 該注解只能標(biāo)記在"有且僅有一個(gè)抽象方法"的接口上
• JDK8接口中可以定義靜態(tài)方法和默認(rèn)方法（方法默認(rèn)實(shí)現(xiàn)default），都不算是抽象方法

public class Test {@FunctionalInterfaceinterface Print{String print(String str,String str1);}public static void main(String[] args) {Print print=(str,str1)-> {System.out.println("hello word! "+str+str1);return str+str1;};System.out.println(print.print("ruoye", "yoya"));} }

3、接口調(diào)整

方便接口擴(kuò)展

jdk8之前接口只能有靜態(tài)常量和抽象方法

jdk8后接口可以有默認(rèn)方法和靜態(tài)方法

public interface Print{public static void aaa(){System.out.println("aaa");}public default void bbb(){System.out.println("bbb");}String print(String str,String str1); }

4、方法引用

::

5、Stream（流水線）

• 集合遍歷有弊端
• 篩選
• 切片
• 映射
• 查找
• 去重
• 統(tǒng)計(jì)
• 匹配
• 歸約

特性

• Stream只能操作一次

• Stream方法返回的是新的流

• Stream不調(diào)用終結(jié)方法，中間的操作不會(huì)執(zhí)行

5.1、Stream的獲取

public class Test {public static void main(String[] args) {//集合List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu");Stream<String> stream = strings.stream();//數(shù)組String[] strings1={"zhangsan", "lisi", "wangwu", "zhaoliu"};Stream<String> stream1 = Stream.of(strings1);//map可以通過獲取鍵集合，值集合，從而獲得流} }

5.2、常用方法

方法聲明功能介紹返回值方法類型

count	統(tǒng)計(jì)個(gè)數(shù)	long	終結(jié)
forEach	逐一處理	void	終結(jié)
filter	過濾	Stream	函數(shù)拼接
limit	取用前幾個(gè)	Stream	函數(shù)拼接
skip	跳過前幾個(gè)	Stream	函數(shù)拼接
map	映射	Stream	函數(shù)拼接
concat	組合	Stream	函數(shù)拼接

5.3、forEach

public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu");strings.stream().forEach(System.out::println);} }

5.4、count

public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu");System.out.println(strings.stream().count());} }

5.5、filter

public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu");strings.stream().filter(s -> s.startsWith("z")).forEach(System.out::println);} }

5.6、limit

public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu");strings.stream().limit(1).forEach(System.out::println);} }

5.7、skip

public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu");strings.stream().skip(1).forEach(System.out::println);} }

5.8、map

完成數(shù)據(jù)轉(zhuǎn)換、處理

public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu");strings.stream().map(s->s+="yoya").forEach(System.out::println);} }

5.9、sorted

public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu");strings.stream().sorted().forEach(System.out::println);} }

5.10、distinct

Stream流中的distinct方法對(duì)于基本數(shù)據(jù)類型是可以直接出重的，但是對(duì)于自定義類型，需要重寫hashCode和equals方法來移除重復(fù)元素

public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu","zhangsan");strings.stream().distinct().forEach(System.out::println);} }

5.11、match

public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu","zhangsan");System.out.println(strings.stream().anyMatch(s -> s.startsWith("z")));} } public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu","zhangsan");System.out.println(strings.stream().allMatch(s -> s.startsWith("z")));} } public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu","zhangsan");System.out.println(strings.stream().noneMatch(s -> s.startsWith("z")));} }

5.12、find

findfirst返回第一個(gè)元素

findany返回隨機(jī)一個(gè)元素

public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu","zhangsan");Optional<String> z = strings.stream().filter(s -> s.startsWith("z")).findAny();System.out.println(z.get());} }

5.13、max，min

public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu","zhangsan");Optional<String> max = strings.stream().max((s1, s2) -> {return s1.compareTo(s2);});System.out.println(max.get());} } public class Test {public static void main(String[] args) {List<String> strings = Arrays.asList("zhangsan", "lisi", "wangwu", "zhaoliu","zhangsan");Optional<String> max = strings.stream().min((s1, s2) -> {return s1.compareTo(s2);});System.out.println(max.get());} }

5.14、reduce

歸約

public class Test {public static void main(String[] args) {Integer reduce = Stream.of(1, 2, 3, 4, 5).reduce(0, (a, b) -> {return a + b;});System.out.println(reduce);} }

5.15、mapToInt

轉(zhuǎn)為int

public class Test {public static void main(String[] args) {Integer[] integers={1, 2, 3, 4, 5};Stream.of(integers).mapToInt(Integer::intValue).forEach(System.out::println);} }

5.16、concat

合并流

public class Test {public static void main(String[] args) {Integer[] integers={1, 2, 3, 4, 5};Integer[] integers1={6,7,8,9,10};Stream<Integer> concat = Stream.concat(Stream.of(integers), Stream.of(integers1));concat.mapToInt(Integer::intValue).forEach(System.out::println);} }

5.17、結(jié)果收集

public class Test {public static void main(String[] args) {Integer[] integers={1, 2, 3, 4, 5};Integer[] integers1={6,7,8,9,10};Stream<Integer> concat = Stream.concat(Stream.of(integers), Stream.of(integers1));List<Integer> collect = concat.collect(Collectors.toList());System.out.println(collect);} } public class Test {public static void main(String[] args) {Integer[] integers={1, 2, 3, 4, 5};Integer[] integers1={6,7,8,9,10};Stream<Integer> concat = Stream.concat(Stream.of(integers), Stream.of(integers1));List<Integer> collect = concat.collect(Collectors.toCollection(ArrayList::new));System.out.println(collect);} } public class Test {public static void main(String[] args) {Integer[] integers={1, 2, 3, 4, 5};Integer[] integers1={6,7,8,9,10};Stream<Integer> concat = Stream.concat(Stream.of(integers), Stream.of(integers1));Integer[] integers2 = concat.toArray(Integer[]::new);System.out.println(Arrays.toString(integers2));} }

5.19、聚合

public class Test {public static void main(String[] args) {Person person0 = new Person(1, "zhangsan", true);Person person1 = new Person(2, "lisi", true);Person person2 = new Person(3, "wangwu", false);Person person3 = new Person(4, "zhaoliu", true);Person person4 = new Person(5, "qianqi", true);Stream<Person> person = Stream.of(person0, person1, person2, person3, person4);Optional<Person> collect = person.collect(Collectors.maxBy((p1, p2) -> {return p1.getId() - p2.getId();}));System.out.println(collect.get());} } public class Test {public static void main(String[] args) {Person person0 = new Person(1, "zhangsan", true);Person person1 = new Person(2, "lisi", true);Person person2 = new Person(3, "wangwu", false);Person person3 = new Person(4, "zhaoliu", true);Person person4 = new Person(5, "qianqi", true);Stream<Person> person = Stream.of(person0, person1, person2, person3, person4);Integer collect = person.collect(Collectors.summingInt(p -> p.getId()));System.out.println(collect);} } public class Test {public static void main(String[] args) {Person person0 = new Person(1, "zhangsan", true);Person person1 = new Person(2, "lisi", true);Person person2 = new Person(3, "wangwu", false);Person person3 = new Person(4, "zhaoliu", true);Person person4 = new Person(5, "qianqi", true);Stream<Person> person = Stream.of(person0, person1, person2, person3, person4);Double collect = person.collect(Collectors.averagingInt(Person::getId));System.out.println(collect);} } public class Test {public static void main(String[] args) {Person person0 = new Person(1, "zhangsan", true);Person person1 = new Person(2, "lisi", true);Person person2 = new Person(3, "wangwu", false);Person person3 = new Person(4, "zhaoliu", true);Person person4 = new Person(5, "qianqi", true);Stream<Person> person = Stream.of(person0, person1, person2, person3, person4);Long collect = person.collect(Collectors.counting());System.out.println(collect);} }

5.20、分組

public class Test {public static void main(String[] args) {Person person0 = new Person(1, "zhangsan", true);Person person1 = new Person(2, "lisi", true);Person person2 = new Person(3, "zhangsan", false);Person person3 = new Person(4, "lisi", true);Person person4 = new Person(5, "zhangsan", true); // Stream<Person> person = Stream.of(person0, person1, person2, person3, person4); // Map<String, List<Person>> collect = person // .collect(Collectors.groupingBy(person5 -> person5.getName())); // System.out.println(collect);// Stream<Person> person = Stream.of(person0, person1, person2, person3, person4); // Map<String, List<Person>> collect = person // .collect(Collectors.groupingBy(person5 -> person5.isGender()?"男":"女")); // System.out.println(collect);Stream<Person> person = Stream.of(person0, person1, person2, person3, person4);Map<String, Map<String, List<Person>>> collect = person.collect(Collectors.groupingBy(person5 -> person5.getName(), Collectors.groupingBy(person5 -> person5.isGender() ? "男" : "女")));System.out.println(collect);} }

5.21、分區(qū)

public class Test {public static void main(String[] args) {Person person0 = new Person(1, "zhangsan", true);Person person1 = new Person(2, "lisi", true);Person person2 = new Person(3, "zhangsan", false);Person person3 = new Person(4, "lisi", true);Person person4 = new Person(5, "zhangsan", true);Stream<Person> person = Stream.of(person0, person1, person2, person3, person4);Map<Boolean, List<Person>> collect = person.collect(Collectors.partitioningBy(person5 -> person5.isGender()));System.out.println(collect);} }

5.22、joining

public class Test {public static void main(String[] args) {Person person0 = new Person(1, "zhangsan", true);Person person1 = new Person(2, "lisi", true);Person person2 = new Person(3, "zhangsan", false);Person person3 = new Person(4, "lisi", true);Person person4 = new Person(5, "zhangsan", true);// Stream<Person> person = Stream.of(person0, person1, person2, person3, person4); // String collect = person // .map(person5 -> person5.getName()) // .collect(Collectors.joining()); // System.out.println(collect); // // Stream<Person> person = Stream.of(person0, person1, person2, person3, person4); // String collect = person // .map(person5 -> person5.getName()) // .collect(Collectors.joining("_")); // System.out.println(collect);Stream<Person> person = Stream.of(person0, person1, person2, person3, person4);String collect = person.map(person5 -> person5.getName()).collect(Collectors.joining("_","###","$$$"));System.out.println(collect);} }

5.23、并行流

public class Test {public static void main(String[] args) {Person person0 = new Person(1, "zhangsan", true);Person person1 = new Person(2, "lisi", true);Person person2 = new Person(3, "zhangsan", false);Person person3 = new Person(4, "lisi", true);Person person4 = new Person(5, "zhangsan", true);Stream<Person> person01 = Stream.of(person0, person1, person2, person3, person4).parallel();person01.map(s->{System.out.println(Thread.currentThread()+"==="+s);return s;}).forEach(System.out::println);} }

并行流出現(xiàn)問題可嘗試使用同步代碼塊

6、日期

• 設(shè)計(jì)不合理，在java.util和java.sql的包中都有日期類，java.util.Date同時(shí)包含日期和時(shí)間的，而 java.sql.Date僅僅包含日期，此外用于格式化和解析的類在java.text包下
• 非線程安全，java.util.Date是非線程安全的，所有的日期類都是可變的，這是java日期類最大的問 題之一
• 時(shí)區(qū)處理麻煩，日期類并不提供國(guó)際化，沒有時(shí)區(qū)支持

JDK 8中增加了一套全新的日期時(shí)間API，這套API設(shè)計(jì)合理，是線程安全（每次都返回新對(duì)象）的，新的日期及時(shí)間API位于java.time包

• LocalDate ：表示日期，包含年月日，格式為 2019-10-16
• LocalTime ：表示時(shí)間，包含時(shí)分秒，格式為 16:38:54.158549300
• LocalDateTime ：表示日期時(shí)間，包含年月日，時(shí)分秒，格式為 2018-09-06T15:33:56.750
• DateTimeFormatter ：日期時(shí)間格式化類
• Instant：時(shí)間戳，表示一個(gè)特定的時(shí)間瞬間
• Duration：用于計(jì)算2個(gè)時(shí)間(LocalTime，時(shí)分秒)的距離
• Period：用于計(jì)算2個(gè)日期(LocalDate，年月日)的距離
• ZonedDateTime ：包含時(shí)區(qū)的時(shí)間

6.1、LocalDate

public class Test {public static void main(String[] args) {//指定日期創(chuàng)建LocalDate localDate=LocalDate.of(2020,10,19);System.out.println(localDate);//當(dāng)前日期創(chuàng)建System.out.println(LocalDate.now());//更改日期LocalDate localDate1 = localDate.withMonth(11);System.out.println(localDate1);//日期增減（plus，minus）LocalDate localDate2 = localDate1.plusDays(1);System.out.println(localDate2);//日期比較System.out.println(localDate.isAfter(localDate1));System.out.println(localDate.isBefore(localDate1));} }

6.2、LocalTime

public class Test {public static void main(String[] args) {//指定時(shí)間創(chuàng)建LocalTime localTime=LocalTime.of(10,19,0,123);System.out.println(localTime);//當(dāng)前時(shí)間創(chuàng)建System.out.println(LocalTime.now());//時(shí)間更改LocalTime localTime1 = localTime.withHour(11);System.out.println(localTime1);//時(shí)間增減（plus，minus）LocalTime localTime2 = localTime1.plusHours(1);System.out.println(localTime2);//時(shí)間比較同上} }

6.3、LocalDateTime

public class Test {public static void main(String[] args) {LocalDate now = LocalDate.now();LocalTime now1 = LocalTime.now();LocalDateTime now2 = LocalDateTime.now();System.out.println(LocalDateTime.of(now,now1));System.out.println(now2);//同樣有設(shè)置、增減、比較} }

6.4、DateTimeFormatter

日期時(shí)間格式化與解析

public class Test {public static void main(String[] args) {LocalDateTime now = LocalDateTime.now();DateTimeFormatter dateTimeFormatter=DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");System.out.println(dateTimeFormatter.format(now));String str="2021-07-16 11:03:00";LocalDateTime parse = LocalDateTime.parse(str, dateTimeFormatter);System.out.println(parse);} }

6.5、Instant

public class Test {public static void main(String[] args) {Instant instant=Instant.now();System.out.println(instant.getNano());} }

6.6、Duration、Period

Duration：時(shí)間差

Period：日期差

public class Test {public static void main(String[] args) {Duration duration = Duration.between(LocalTime.now(), LocalTime.of(12, 0, 0, 0));System.out.println(duration.toHours());System.out.println(duration.toMinutes());System.out.println(duration.toMillis());} } public class Test {public static void main(String[] args) {Period period = Period.between(LocalDate.now(), LocalDate.of(2022, 5, 2));System.out.println(period.getDays());System.out.println(period.getMonths());System.out.println(period.getYears());} }

6.7、時(shí)區(qū)

public class Test {public static void main(String[] args) {//所有時(shí)區(qū)for (String availableZoneId : ZoneId.getAvailableZoneIds()) {System.out.println(availableZoneId);}//獲取標(biāo)準(zhǔn)時(shí)間ZonedDateTime zonedDateTime=ZonedDateTime.now(Clock.systemUTC());System.out.println(zonedDateTime);//獲取默認(rèn)時(shí)區(qū)時(shí)間ZonedDateTime zonedDateTime1=ZonedDateTime.now();System.out.println(zonedDateTime1);//獲取指定時(shí)區(qū)世家ZonedDateTime zonedDateTime2=ZonedDateTime.now(ZoneId.of("America/Cuiaba"));System.out.println(zonedDateTime2);} }

7、@Repeatable

允許重復(fù)注解

8、@Target屬性

ElementType.TYPE_PARAMETER：允許注解寫在聲明語句中

ElementType.TYPE_USE：任何定義的地方都可以用

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