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DeleiGuo
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add features demo
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‎source/java/interview/src/main/java/cn/delei/java/feature/LambdaDemo.java‎

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package cn.delei.java.feature;
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import cn.delei.util.PrintUtil;
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import java.io.PrintWriter;
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import java.util.*;
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import java.util.function.Consumer;
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import java.util.function.Predicate;
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import java.util.stream.Stream;
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/**
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* Lambda 函数编程 Demo
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*
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* @author deleiguo
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* @since 1.8
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*/
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public class LambdaDemo {
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public static void main(String[] args) {
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List<String> strList = Arrays.asList("delei", "guo", "Java", "PHP", "Go");
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List<Integer> intList = Arrays.asList(new Integer[]{10, 8, 21, 33});
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// ==> 构造
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new Thread(() -> {
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System.out.println(Thread.currentThread().getName() + " Start");
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}, "T01");
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Collections.sort(intList, Integer::compareTo);
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Collections.sort(intList, (Integer i1, Integer i2) -> {
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return i1 - i2;
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});
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PrintUtil.printDivider("forEach");
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// ==> forEach
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strList.forEach(new Consumer<String>() {
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@Override
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public void accept(String s) {
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System.out.print(s + " ");
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}
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});
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System.out.println();
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strList.forEach(s -> {
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System.out.print(s + " ");
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});
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System.out.println();
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Map<Integer, Integer> map = new HashMap<>();
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map.put(1, 1);
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map.put(10, 10);
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map.forEach((k, v) -> System.out.println("key=" + k + " ,value=" + v));
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PrintUtil.printDivider("方法引用");
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// ==> 方法引用，由::双冒号操作符标识
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strList.forEach(System.out::println);
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PrintUtil.printDivider("Predicate");
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// ==> Predicate
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Predicate<String> conditon = (str) -> str.length() > 4;
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filter(strList, conditon);
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conditon = (str) -> str.startsWith("delei");
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filter(strList, conditon);
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conditon = (str) -> true;
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filter(strList, conditon);
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conditon = (str) -> false;
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filter(strList, conditon);
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}
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static void filter(List<String> list, Predicate<String> predicate) {
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list.stream().filter((s) -> (predicate.test(s))).forEach((s) -> {
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System.out.println(s + " ");
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});
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}
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}
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‎source/java/interview/src/main/java/cn/delei/java/feature/LambdaFunctionalInterface.java‎

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package cn.delei.java.feature;
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/**
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* Lambda Functional Interface
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* @author deleiguo
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*/
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@FunctionalInterface
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public interface LambdaFunctionalInterface {
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void func();
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}

‎source/java/interview/src/main/java/cn/delei/java/feature/LocalDateDemo.java‎

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package cn.delei.java.feature;
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import cn.delei.util.PrintUtil;
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import java.time.*;
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import java.time.format.DateTimeFormatter;
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import java.time.temporal.ChronoUnit;
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/**
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* LocalDate 日期类 Demo
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*
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* @author deleiguo
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* @since 1.8
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*/
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public class LocalDateDemo {
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public static void main(String[] args) {
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// ==> Clock
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PrintUtil.printDivider("Clock");
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Clock clock = Clock.systemUTC();
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System.out.println(clock.millis());
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clock = Clock.systemDefaultZone();
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System.out.println("ZoneId=" + clock.getZone());
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clock = Clock.system(ZoneId.of("Europe/Paris")); // 巴黎时区
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System.out.println(clock.millis()); // 每次调用将返回当前瞬时时间(UTC)
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clock = Clock.system(ZoneId.of("Asia/Shanghai"));// 上海时区
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System.out.println(clock.millis());// 每次调用将返回当前瞬时时间(UTC)
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// ==> Instant时间戳
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PrintUtil.printDivider("Instant 时间戳");
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Instant instant = Instant.now();
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System.out.println("toEpochMilli=" + instant.toEpochMilli()); //精确到毫秒
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System.out.println("getNano=" + instant.getNano());
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System.out.println("getEpochSecond=" + instant.getEpochSecond()); //精确到秒 得到相对于1970-01-01 00:00:00 UTC的一个时间
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System.out.println("toString=" + instant.toString());
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// ==> 格式化
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PrintUtil.printDivider("格式化");
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LocalDate localDate = LocalDate.now();
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System.out.println(String.format("date now : %s", localDate));
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LocalDateTime localDateTime = LocalDateTime.now().withNano(0);
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System.out.println(String.format("time now : %s", localDateTime));
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localDateTime = LocalDateTime.now(ZoneId.of("Europe/Paris"));
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System.out.println(String.format("Europe/Paris now : %s", localDateTime));
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// 必须指定时区
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ZonedDateTime zonedDateTime = ZonedDateTime.of(LocalDateTime.now(), ZoneId.systemDefault());
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System.out.println(format(localDateTime));
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System.out.println(format(zonedDateTime));
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System.out.println(format(LocalDateTime.now()));
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// ==> 字符串转日期
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PrintUtil.printDivider("字符串转日期");
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localDate = LocalDate.of(2019, 12, 20);
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System.out.println(" LocalDate.of: " + format(localDate));
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localDate = LocalDate.parse("2021-04-19");
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System.out.println(" LocalDate.parse: " + format(localDate));
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localDateTime = LocalDateTime.of(2019, 12, 20, 23, 10, 59);
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System.out.println(" LocalDateTime.of: " + format(localDateTime));
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localDateTime = LocalDateTime.parse("2021-04-19T15:54:54");
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System.out.println(" LocalDateTime.parse: " + format(localDateTime));
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// ==> 日期获取
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PrintUtil.printDivider("日期获取");
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localDate = LocalDate.of(2019, 12, 20);
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localDateTime = LocalDateTime.of(2019, 12, 20, 23, 10, 59, 889);
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System.out.println("日期 " + format(localDateTime));
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System.out.println("年份：" + localDateTime.getYear());
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System.out.println("月份：" + localDateTime.getMonth());
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System.out.println("当年中的第多少天：" + localDateTime.getDayOfYear());
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System.out.println("当月的第多少天：" + localDateTime.getDayOfMonth());
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System.out.println("星期：" + localDateTime.getDayOfWeek());
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System.out.println("时：" + localDateTime.getHour());
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System.out.println("分：" + localDateTime.getMinute());
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System.out.println("秒：" + localDateTime.getSecond());
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System.out.println("毫秒：" + localDateTime.getNano());
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System.out.println("是否闰年：" + localDate.isLeapYear());
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// ==> 日期计算
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PrintUtil.printDivider("日期计算");
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LocalDate aferCalc;
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localDate = LocalDate.now();
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System.out.println("日期 " + format(localDate));
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aferCalc = localDate.plusWeeks(1L);
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System.out.println("一周后:" + format(aferCalc));
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aferCalc = localDate.plusDays(20L);
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System.out.println("20后:" + format(aferCalc));
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aferCalc = localDate.minusDays(20L);
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System.out.println("20天前:" + format(aferCalc));
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aferCalc = localDate.plus(1, ChronoUnit.WEEKS);
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System.out.println("2周后 plus ChronoUnit:" + format(aferCalc));
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PrintUtil.printDivider("日期相隔");
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LocalDate date01 = LocalDate.of(2008, 12, 25);
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LocalDate date02 = LocalDate.of(2019, 3, 11);
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System.out.println("日期01: " + format(date01));
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System.out.println("日期02: " + format(date02));
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Period period = Period.between(date01, date02);
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// 这里period.getDays()得到的天是抛去年月以外的天数，并不是总天数
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System.out.println("date01 到 date02 相隔："
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+ period.getYears() + "年"
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+ period.getMonths() + "月"
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+ period.getDays() + "天");
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long day = date02.toEpochDay() - date01.toEpochDay();
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System.out.println("date01 到 date02 相隔：" + day + "天");
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PrintUtil.printDivider("时间相隔");
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LocalDateTime time01 = LocalDateTime.of(2018, 12, 25, 8, 15, 46);
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LocalDateTime time02 = LocalDateTime.of(2019, 3, 11, 13, 10, 35);
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//表示两个瞬时时间的时间段
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System.out.println("时间01: " + format(time01));
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System.out.println("时间02: " + format(time02));
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Duration d1 = Duration.between(time01.toInstant(ZoneOffset.UTC), time02.toInstant(ZoneOffset.UTC));
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//得到相应的时差
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System.out.println(d1.toDays());
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System.out.println(d1.toHours());
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System.out.println(d1.toMinutes());
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System.out.println(d1.toMillis());
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System.out.println(d1.toNanos());
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}
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static String format(LocalDate date) {
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final DateTimeFormatter format = DateTimeFormatter.ofPattern("yyyy-MM-dd");
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return format.format(date);
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}
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static String format(LocalDateTime time) {
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final DateTimeFormatter format = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
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return format.format(time);
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}
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static String format(ZonedDateTime zonedDateTime) {
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final DateTimeFormatter format = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSSSSSZ");
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return format.format(zonedDateTime);
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}
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}

‎source/java/interview/src/main/java/cn/delei/java/feature/OptionalDemo.java‎

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package cn.delei.java.feature;
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import cn.delei.pojo.Person;
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import cn.delei.util.PrintUtil;
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import java.util.Optional;
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/**
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* Optional类 使用
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*
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* @author deleiguo
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*/
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public class OptionalDemo {
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public static void main(String[] args) {
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String parameter = "deleiguo";
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String nullObj = null;
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String nullStr = "";
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// ==> of
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PrintUtil.printDivider("of");
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Optional<String> parameterOptional = Optional.of(parameter);
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Optional<String> nullObjOptional = Optional.of(nullStr);
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// Optional<String> nullStrOptional = Optional.of(nullObj); // throw NPE
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// ==> ofNullable
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PrintUtil.printDivider("ofNullable");
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parameterOptional = Optional.ofNullable(parameter);
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nullObjOptional = Optional.ofNullable(null);
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Optional<String> nullStrOptional = Optional.ofNullable(nullObj);
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// ==> isPresent
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PrintUtil.printDivider("isPresent");
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if (parameterOptional.isPresent()) {
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//在Optional实例内调用get()返回已存在的值
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System.out.println(parameterOptional.get());
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}
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// ==> orElse
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PrintUtil.printDivider("orElse");
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System.out.println(parameterOptional.orElse("There is nobody"));
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System.out.println(nullStrOptional.orElse("There is nobody"));
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System.out.println(nullStrOptional.orElseGet(() -> "default person"));
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// ==> map
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PrintUtil.printDivider("map");
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Optional<String> optional = Optional.ofNullable(parameter).map(s -> s.toUpperCase());
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System.out.println(optional.orElse("No value found"));
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// ==> 高频使用方法
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Person delei = new Person("deleiguo", 28, "12345678");
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Person nullPerson = null;
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Optional.ofNullable(delei).map(Person::getName);
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}
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}

‎source/java/interview/src/main/java/cn/delei/java/feature/StreamDemo.java‎

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package cn.delei.java.feature;
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import cn.delei.util.PrintUtil;
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import java.util.Arrays;
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import java.util.List;
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import java.util.function.Supplier;
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import java.util.stream.Stream;
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/**
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* Stream API Demo
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*
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* @author deleiguo
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* @since 1.8
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*/
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public class StreamDemo {
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public static void main(String[] args) {
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List<String> strList = Arrays.asList("delei", "guo", "Java", "PHP", "Go", "JavaScript", "", "", "Java",
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"deleiguo", "Go", "PHP");
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/*
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* 无法重用此 Stream 对象
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* java.lang.IllegalStateException: stream has already been operated upon or closed
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*
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* 运行如下代码会报上述错误
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* <code>
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* streamSupplier.get().forEach(System.out::println);
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* streamSupplier.get().forEach(System.out::println);
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* </code>
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*/
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Stream<String> strStream = strList.stream();
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// 重用 Stream，使用 get 方法每次获取一个新的 stream
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Supplier<Stream<String>> streamSupplier = () -> strList.stream();
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// ==> forEach
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PrintUtil.printDivider("forEach");
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streamSupplier.get().forEach(s -> {
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System.out.print(s + " ");
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});
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System.out.println();
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streamSupplier.get().forEach(System.out::print);
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System.out.println();
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// ==> filter
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PrintUtil.printDivider("filter");
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long count = streamSupplier.get().filter(s -> "deleiguo".equals(s)).count();
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System.out.println("filter count:" + count);
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streamSupplier.get().filter(s -> s.startsWith("Java")).forEach(s -> {
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System.out.print(s + " ");
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});
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System.out.println();
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// ==> limit
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PrintUtil.printDivider("limit");
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streamSupplier.get().limit(3).forEach(s -> {
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System.out.print(s + " ");
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});
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System.out.println();
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// ==> map
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PrintUtil.printDivider("map");
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streamSupplier.get().map(s -> s + "-after").forEach(s -> {
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System.out.print(s + " ");
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});
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System.out.println();
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// ==> match
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PrintUtil.printDivider("match");
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System.out.println(streamSupplier.get().anyMatch(s -> s.startsWith("Java")));
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System.out.println(streamSupplier.get().allMatch(s -> s.startsWith("Java")));
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// ==> skip
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PrintUtil.printDivider("skip");
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streamSupplier.get().skip(2).forEach(s -> {
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System.out.print(s + " ");
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});
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System.out.println();
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}
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}

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