JDK9的新特性之String压缩和字符编码的实现方法

public final class String
 implements java.io.Serializable, Comparable<String>, CharSequence {
 
 //The value is used for character storage.
 private final char value[];
}

public final class String
 implements java.io.Serializable, Comparable<String>, CharSequence {
 
 /** The value is used for character storage. */
 @Stable
 private final byte[] value;

 private final byte coder;

 @Native static final byte LATIN1 = 0;
 @Native static final byte UTF16 = 1;

 static final boolean COMPACT_STRINGS;

 static {
  COMPACT_STRINGS = true;
 }

package time;
import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;
import java.util.Calendar;
import java.util.Date;
/***
 * 总结: java.util.Date和 SimpleDateFormat 都是非线程安全的
 * 1. LocalDate
 * 2. LocalTime
 * 3. LocalDateTime
 * 4. DateTimeFormatter
 * 5. ChronoUnit
 */
public class Java8Date {
  public static void main(String[] args) {
    /** #0. Calendar
     * 区别于calendar的month: canlendar中:[]
     * 1. LocalDate的年月日直接是日期中的值;
     * 2. date.getMonthValue() 和 c.get(Calendar.MONTH) 有区别: c:0表示1月
     */
    Calendar c = Calendar.getInstance(); // 测试日期:2019-04-02
    System.out.println(c.get(Calendar.YEAR)); // 2019
    System.out.println(c.get(Calendar.MONTH)); // 3(0=1月)
    System.out.println(c.get(Calendar.DAY_OF_MONTH)); //2
    // #1. LocalDate 2019-04-02 : 今日日期: LocalDate.now()
    System.out.println("=-==-==-==-==-==-==-==-==-==-==");
    LocalDate date = LocalDate.now();
    System.out.println(date); // 2019-04-02
    // #2. year month day: 年月日获取
    System.out.println("=-==-==-==-==-==-==-==-==-==-==");
    int year = date.getYear(); // 2019
    int month = date.getMonthValue();// 4
    int day = date.getDayOfMonth(); // 2
    System.out.println(year + "-" + month + "-" + day); // 2019-4-2
    // #3. 构造日期: 给定年月日
    System.out.println("=-==-==-==-==-==-==-==-==-==-==");
    LocalDate dt1 = LocalDate.of(2019, 3, 8);
    LocalDate dt2 = LocalDate.of(2019, 3, 8);
    // #4. 日期比较: equals
    // true: 内部是比较的 year-year month-month day-day
    System.out.println(dt2.equals(dt1)); 
    // #5. 周期性日期, 比如: 判断用户的生日
    System.out.println("=-==-==-==-==-==-==-==-==-==-==");
    // 生日:0308
    MonthDay uBirth = MonthDay.of(3, 8);
    MonthDay dtMD = MonthDay.from(dt1);
    // dt1 是不是 用户u的生日:true
    System.out.println("dt1==用户u的生日:" + dtMD.equals(uBirth));
    // #6. 获取当前时间 [HH:mm:ss.SSS]
    System.out.println("=-==-==-==-==-==-==-==-==-==-==");
    LocalTime time = LocalTime.now();
    System.out.println(time);
    // #7. 增减时间 plus/minus
    System.out.println("=-==-==-==-==-==-==-==-==-==-==");
    // dt1=2019-03-08
    LocalDate dt1Plus2d = dt1.plusDays(2); 
    LocalDate dt1Plus2y = dt1.plusYears(2); 
    LocalDate dt1Plus2m = dt1.plusMonths(2);
    System.out.println(dt1Plus2d); // 2019-03-10
    System.out.println(dt1Plus2y); // 2021-03-08
    System.out.println(dt1Plus2m); // 2019-05-08
    // dt1=2019-03-08
    LocalDate plus1w = dt1.plus(1, ChronoUnit.WEEKS);
    LocalDate plus1d = dt1.plus(1, ChronoUnit.DAYS);
    LocalDate plus18y = dt1.plus(18, ChronoUnit.YEARS);
    LocalDate minus1y = dt1.minus(1, ChronoUnit.YEARS);
    System.out.println(plus1w); // 2019-03-15
    System.out.println(plus1d); // 2019-03-09
    System.out.println(plus18y); // 2037-03-08
    System.out.println(minus1y); // 2018-03-08
    // #8. 日期dt1 早于/晚于 minus1y
    System.out.println("=-==-==-==-==-==-==-==-==-==-==");
    // dt1=2019-03-08 minus1y=2018-03-08
    System.out.println(dt1.isAfter(minus1y)); // true
    System.out.println(dt1.isBefore(minus1y)); // false
    // #9. 计算日期差
    System.out.println("=-==-==-==-==-==-==-==-==-==-==");
    // dt1=2019-03-08 dt20190402
    LocalDate dt20190402 = LocalDate.of(2019, 4, 2);
    Period btPeriod = Period.between(dt1, dt20190402);
    Period btPeriod2 = Period.between(dt1, dt20190402);
    System.out.println(btPeriod); // P25D
    System.out.println(btPeriod.getMonths()); // 0
    System.out.println(btPeriod.getDays()); // 25
    // 25 可见是标量, 不是矢量, 只计算差数
    System.out.println(btPeriod2.getDays()); 
    // #10. 时间戳Instant->java.util.Date[getTime()==toEpochMilli()]
    System.out.println("=-==-==-==-==-==-==-==-==-==-==");
    Instant now = Instant.now(); // 2019-04-02T08:48:46.755Z
    Date dtNow = Date.from(now); // Tue Apr 02 16:48:46 CST 2019
    long millisInstant = now.toEpochMilli();
    long millisDate = dtNow.getTime();
    System.out.println(millisInstant); // 1554195038598
    System.out.println(millisDate); // 1554195038598
    // #11# ** 日期格式化
    System.out.println("=-==-==-==-==-==-==-==-==-==-==");
    DateTimeFormatter pattern1 = DateTimeFormatter.ofPattern("yyyyMMdd-HH:mm:ss,SSS");
    DateTimeFormatter pattern2 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    /**
     * 命题:--> 将 "20190215-22:10:30,333" 日期
     * 格式化为 "yyyyMMdd-HH mm:ss.SSS" 字符串
     * @.1. 字符串转对象LocalDateTime
     * @.2. LocalDateTime对象转字符串
     */
    String strDt = "20190215-22:10:30,333"; // @.1.
    LocalDateTime dateTime = LocalDateTime.parse(strDt, pattern1); 
    String fmtDtString = dateTime.format(pattern2); // @.2.
    System.out.println(dateTime); // 2019-02-15T22:10:30.333
    System.out.println(fmtDtString); // 2019-02-15 22:10:30
    System.out.println("=-==-==-==-==-==-==-==-==-==-==");
  }
}