JavaTimeDemo.java

Download JavaTimeDemo.java

  1: // A sampling of the Java 8 Date and Time APIs.  This program demos various
  2: //  tasks one might do using the new APIs.
  3: // Written 11/2014
  4: 
  5: import java.util.Scanner;
  6: import java.time.*;
  7: import java.time.format.*;
  8: import java.time.zone.*;
  9: import static java.time.temporal.TemporalAdjusters.*;
 10: 
 11: /** @author Wayne Pollock
 12:  */
 13: 
 14: public class JavaTimeDemo {
 15: 
 16:    public static void main ( String[] args ) {
 17:       // How to time something:
 18:       System.out.println( "\nStarting timer...." );
 19:       Instant start = Instant.now();
 20:       Scanner in = new Scanner( System.in );
 21:       System.out.print( "\tWhat is \"2 + 3\"? " );
 22:       String answer = in.nextLine();
 23:       Instant end = Instant.now();
 24:       System.out.println("Starting Instant: " + start
 25:          + " (in ISO-8601 format)" );
 26:       long duration = Duration.between(start, end).getSeconds();
 27:       System.out.println( "You took " + duration
 28:          + " seconds to work that out!\n" );
 29: 
 30:       // How to format a LocalDate as a human-readable string:
 31:       DateTimeFormatter myFormat =
 32:          DateTimeFormatter.ofPattern( "MMM d yyyy  hh:mm a" );
 33:       DateTimeFormatter dateOnly =
 34:          DateTimeFormatter.ofLocalizedDate( FormatStyle.FULL );
 35:       LocalDateTime now = LocalDateTime.now();
 36:       System.out.println( "Default format of LocalDateTime: " + now );
 37:       System.out.println( "Date-only part (as FULL): "
 38:          + dateOnly.format(now) );
 39:       System.out.println( "Custom Format: " + myFormat.format(now) );
 40:       System.out.printf( "Using printf: %tD%n", now );
 41: 
 42:       // Parse a String to a LocalDateTime:
 43:       DateTimeFormatter inputFormat =
 44:          DateTimeFormatter.ofPattern( "M/d/yy h:m a" );
 45:       String someDate = "7/9/14 3:40 PM";
 46:       System.out.print( "\nEnter a date and time (e.g., \""
 47:          + someDate + "\"): " );
 48:       LocalDateTime dateTime;
 49:       for ( ; ; ) {
 50:          try {
 51:             someDate = in.nextLine();
 52:             dateTime = LocalDateTime.parse( someDate, inputFormat );
 53:             break;
 54:          }
 55:          catch ( DateTimeParseException pe )
 56:          { System.out.print( "Invalid date and time format, "
 57:              + "please try again: " );
 58:          }
 59:       }
 60:       System.out.println( "You entered: " + dateTime );
 61: 
 62:       // Extract parts of a LocalDateTime (two ways):
 63:       DayOfWeek day = dateTime.getDayOfWeek();
 64:       System.out.printf( "That is a %tA, or %s%n", dateTime, day );
 65: 
 66:       Period period =
 67:          Period.between(dateTime.toLocalDate(), now.toLocalDate() );
 68:       // Convert Period representation into English:
 69:       String pStr = period.toString().replaceFirst( "P-?", "" );
 70:       pStr = pStr.replaceAll("Y-?", " years, " );
 71:       pStr = pStr.replaceAll("M-?", " months, " );
 72:       pStr = pStr.replaceAll("D", " days " );
 73:       System.out.print( "That is " + pStr );
 74:       if ( dateTime.isAfter(now) )
 75:          System.out.println( "from now.\n" );
 76:       else
 77:          System.out.println( "ago.\n" );
 78: 
 79:       // Performing date arithmetic:
 80:       LocalDate ldom = now.with( lastDayOfMonth() ).toLocalDate();
 81:       System.out.println( "Last day of this month: " + ldom );
 82:       System.out.println( "90 days from today: " + now.plusDays(90) );
 83: 
 84:       // Using ZonedDateTime:
 85:       System.out.println( "\nThe default Time zone on this computer is: "
 86:          + ZoneId.systemDefault() );
 87:       ZonedDateTime myTime = ZonedDateTime.of( now,  ZoneId.systemDefault());
 88: 
 89:       System.out.println( "Some available time zones:" );
 90:       int count = 0;
 91:       for ( String tz : ZoneId.getAvailableZoneIds() ) {
 92:          System.out.println( tz );
 93:          ++count;
 94:          if ( count > 15 )
 95:             break;  // No need to show more zones than that.
 96:       }
 97:       System.out.print( "Pick a time zone: " );
 98:       String zoneName = in.nextLine();
 99:       ZoneId selectedZone = null;
100:       try {
101:          selectedZone = ZoneId.of( zoneName );
102:       } catch ( DateTimeException tde ) {
103:          System.err.println( "Invalid time zone entered; using UTC.");
104:          selectedZone = ZoneOffset.UTC;
105:       }
106: 
107:       ZonedDateTime selectedDateTime = ZonedDateTime.of( now, selectedZone );
108:       System.out.println( "In that time zone, it is currently: "
109:          + selectedDateTime.format( DateTimeFormatter.RFC_1123_DATE_TIME ) );
110:       System.out.println( "Or, in other words: " + selectedDateTime.format(
111:             DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL) ) );
112:    }
113: }