JDK8 部分代码测试

JDK8 部分代码测试

• Lambda 表达式 -

 (p1, p2) -> p1.firstName

（）放参数，可不带类型

->  特定

{ } 方法块 或者一行代码；

(intx,int y) -> x + y   //两整形参数，返回它们的和

() -> 42                  //无参数，直接返回 42

x -> 100;                 //可推断出参数 x 的类型

(String s) -> { System.out.println(s); }//传入一个字符，只执行一个操作，无返回值

• “::” 域操作符
  

JDK8 又重新借用了 C++ 的那个 “::” 域操作符，全称为作用域解析操作符。

• 测试代码
  

package com.test.jdk;import java.time.Clock;import java.time.DayOfWeek;import java.time.Instant;import java.time.LocalDate;import java.time.LocalDateTime;import java.time.LocalTime;import java.time.Month;import java.time.ZoneId;import java.time.format.DateTimeFormatter;import java.time.format.FormatStyle;import java.time.temporal.ChronoField;import java.time.temporal.ChronoUnit;import java.util.ArrayList;import java.util.Arrays;import java.util.Comparator;import java.util.Date;import java.util.LinkedList;import java.util.List;import java.util.Locale;import java.util.UUID;import java.util.concurrent.TimeUnit;import java.util.function.Consumer;import java.util.function.Function;import java.util.function.Supplier;public class JDK8Test {public static void main(String[] args) { Comparator<Person> comparator = (p1, p2) -> p1.firstName .compareTo(p2.firstName); Person p1 = new Person("John", "Doe"); Person p2 = new Person("Alice", "Wonderland"); System.out.println(comparator.compare(p1, p2)); // > 0 System.out.println(comparator.reversed().compare(p1, p2)); // < 0 // Function 接口有一个参数并且返回一个结果， // 并附带了一些可以和其他函数组合的默认方法（compose, andThen）： Function<String, Integer> toInteger = Integer::valueOf; Function<String, String> backToString = toInteger .andThen(String::valueOf); backToString.apply("123"); // "123" System.out.println(backToString); // Supplier 接口返回一个任意范型的值，和Function接口不同的是该接口没有任何参数 Supplier<Object> personSupplier = Object::new; personSupplier.get(); // new Object System.out.println(personSupplier.get()); new Thread(() -> { for (int i = 0; i < 9; i++) { System.out.println(String.format( "Message #%d from inside the thread!", i)); } }).start(); new Thread(() -> { System.out.println(String.format( "Message #%d from inside the thread!", 1024)); }).start(); List inputList = new LinkedList<>(); List upper = new LinkedList<>(); //有问题u// inputList.stream().filter(x -> (x != null &&// x.matches("[A-Z0-9]*"))).into(upper);//// int sumX = inputList.stream()// .filter(x -> (x != null && x.matches("[A-Z0-9]*")))// .map(String::length).reduce(0, Integer::sum);// //从集合中取出每个元素然后打印// List list = new ArrayList<>();// list.add("123aa");// list.add("124aa");// list.add("125aa");// list.forEach(x -> System.out.println(x));// Arrays.asList("Alice", "Bob", "Charlie",// "Dave").forEach(System.out::println);// //names.filter 有问题 啊，，怎么回事啊~！~// List<String> names = Arrays.asList("Alice", "Bob", "Charlie",// "Dave");// List<String> filteredNames = names.filter((e) -> e.length() >= 4)// .into(new ArrayList<String>());//// names.filter(e -> e.length() >= 4)// .forEach(x -> System.out.println(x)); //并行Streams int max = 1000000; List<String> values = new ArrayList<>(max); for (int i = 0; i < max; i++) { UUID uuid = UUID.randomUUID(); values.add(uuid.toString()); } //串行排序： long t0 = System.nanoTime(); long count = values.stream().sorted().count(); System.out.println(count); long t1 = System.nanoTime(); long millis = TimeUnit.NANOSECONDS.toMillis(t1 - t0); System.out.println(String.format("sequential sort took: %d ms", millis)); //并行排序： t0 = System.nanoTime(); count = values.parallelStream().sorted().count(); System.out.println(count); t1 = System.nanoTime(); millis = TimeUnit.NANOSECONDS.toMillis(t1 - t0); System.out.println(String.format("parallel sort took: %d ms", millis)); //DATE API// Clock 时钟Clock clock = Clock.systemDefaultZone(); millis = clock.millis();Instant instant = clock.instant();Date legacyDate = Date.from(instant); // legacy java.util.DateSystem.out.println(legacyDate);// Timezones 时区System.out.println(ZoneId.getAvailableZoneIds());// prints all available timezone idsZoneId zone1 = ZoneId.of("Europe/Berlin");ZoneId zone2 = ZoneId.of("Brazil/East");System.out.println(zone1.getRules());// ZoneRules[currentStandardOffset=+01:00]System.out.println(zone2.getRules());// ZoneRules[currentStandardOffset=-03:00]//LocalTime 本地时间LocalTime now1 = LocalTime.now(zone1);LocalTime now2 = LocalTime.now(zone2);System.out.println(now1.isBefore(now2));  // falselong hoursBetween = ChronoUnit.HOURS.between(now1, now2);long minutesBetween = ChronoUnit.MINUTES.between(now1, now2);System.out.println(hoursBetween);       System.out.println(minutesBetween);     LocalTime late = LocalTime.of(23, 59, 59);System.out.println(late);       // 23:59:59DateTimeFormatter germanFormatter =    DateTimeFormatter        .ofLocalizedTime(FormatStyle.SHORT)        .withLocale(Locale.GERMAN);LocalTime leetTime = LocalTime.parse("13:37", germanFormatter);System.out.println(leetTime);   // 13:37//LocalDate 本地日期LocalDate today = LocalDate.now();LocalDate tomorrow = today.plus(1, ChronoUnit.DAYS);LocalDate yesterday = tomorrow.minusDays(2);LocalDate independenceDay = LocalDate.of(2014, Month.JULY, 4);DayOfWeek dayOfWeek = independenceDay.getDayOfWeek();System.out.println(dayOfWeek); // FRIDAY//从字符串解析一个LocalDate类型和解析LocalTime一样简单： germanFormatter =    DateTimeFormatter        .ofLocalizedDate(FormatStyle.MEDIUM)        .withLocale(Locale.GERMAN);LocalDate xmas = LocalDate.parse("24.12.2014", germanFormatter);System.out.println(xmas);   // 2014-12-24//LocalDateTime 本地日期时间LocalDateTime sylvester = LocalDateTime.of(2014, Month.DECEMBER, 31, 23, 59, 59); dayOfWeek = sylvester.getDayOfWeek();System.out.println(dayOfWeek);      // WEDNESDAYMonth month = sylvester.getMonth();System.out.println(month);          // DECEMBERlong minuteOfDay = sylvester.getLong(ChronoField.MINUTE_OF_DAY);System.out.println(minuteOfDay);    // 1439//只要附加上时区信息，就可以将其转换为一个时间点Instant对象，//Instant时间点对象可以很容易的转换为老式的java.util.Date。 instant = sylvester        .atZone(ZoneId.systemDefault())        .toInstant(); legacyDate = Date.from(instant);System.out.println(legacyDate);     // Wed Dec 31 23:59:59 CET 2014DateTimeFormatter formatter =    DateTimeFormatter        .ofPattern("MMM dd, yyyy - HH:mm");LocalDateTime parsed = LocalDateTime.parse("Nov 03, 2014 - 07:13", formatter);String string = formatter.format(parsed);System.out.println(string);     // Nov 03, 2014 - 07:13}}