Java 8 Novelties

(This is a pretty good walk-through of Java 8 lamba stuff so you can see what it's doing: http://java.dzone.com/articles/java-8-will-revolutionize, but that's not the topic here yet.)

This was the extent of an interface previous to Java 8.

OldTimeClient.java:

package com.etretatlogiciels.defaultmethods;

import java.time.LocalDateTime;

public interface OldTimeClient
{
    void setTime( int hour, int minute, int second );
    void setDate( int day, int month, int year );
    void setDateAndTime( int day, int month, int year, int hour, int minute, int second );
    LocalDateTime getLocalDateTime();
}

OldTimeClient.java:

package com.etretatlogiciels.defaultmethods;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;

public class OldSimpleTimeClient implements OldTimeClient
{
    private LocalDateTime dateAndTime;

    public OldSimpleTimeClient()
    {
        dateAndTime = LocalDateTime.now();
    }

    public void setTime( int hour, int minute, int second )
    {
        LocalDate currentDate = LocalDate.from( dateAndTime );
        LocalTime timeToSet = LocalTime.of( hour, minute, second );
        dateAndTime = LocalDateTime.of( currentDate, timeToSet );
    }

    public void setDate( int day, int month, int year )
    {
        LocalDate dateToSet = LocalDate.of( day, month, year );
        LocalTime currentTime = LocalTime.from( dateAndTime );
        dateAndTime = LocalDateTime.of( dateToSet, currentTime );
    }

    public void setDateAndTime( int day, int month, int year, int hour, int minute, int second )
    {
        LocalDate dateToSet = LocalDate.of( day, month, year );
        LocalTime timeToSet = LocalTime.of( hour, minute, second );
        dateAndTime = LocalDateTime.of( dateToSet, timeToSet );
    }

    public LocalDateTime getLocalDateTime()
    {
        return dateAndTime;
    }

    public String toString()
    {
        return dateAndTime.toString();
    }

    public static void main( String... args )
    {
        TimeClient myTimeClient = new SimpleTimeClient();
        System.out.println( "Testing how this code had to work prior to Java 8...");
        System.out.println( "Current time: " + myTimeClient.toString() );
        System.out.println( "Time in California: " + myTimeClient.getZonedDateTime( "Blah blah" ).toString() );
    }
}

Output:

Testing how this code had to work prior to Java 8...
Current time: 2014-04-03T08:22:53.277
Invalid time zone: Blah blah; using default time zone instead.
Time in California: 2014-04-03T08:22:53.277-06:00[America/Denver]

With Java 8, it's possible to add default and static methods to fall back on. This example demonstrates those in Java 8 and is mostly from http://docs.oracle.com/javase/tutorial/java/IandI/defaultmethods.html.

This URL continues on to demonstrate effects of extending an interface containing a default method...

public interface AnotherTimeClient extends TimeClient
{
    ...
}

...by:

• not mentioning the default method letting caller just use it.
• redefining the method which is tantamount to making it abstract.
• redefining the default method which simply overrides it.

TimeClient.java:

package com.etretatlogiciels.defaultmethods;

import java.time.DateTimeException;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;

public interface TimeClient
{
    void setTime( int hour, int minute, int second );
    void setDate( int day, int month, int year );
    void setDateAndTime( int day, int month, int year, int hour, int minute, int second );
    LocalDateTime getLocalDateTime();

    static ZoneId getZoneId( String zoneString )
    {
        try
        {
            return ZoneId.of( zoneString );
        }
        catch( DateTimeException e )
        {
            System.err.println( "Invalid time zone: " + zoneString + "; using default time zone instead." );
            return ZoneId.systemDefault();
        }
    }

    default ZonedDateTime getZonedDateTime( String zoneString )
    {
        return ZonedDateTime.of( getLocalDateTime(), getZoneId( zoneString ) );
    }
}

SimpleTimeClient.java:

package com.etretatlogiciels.defaultmethods;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;

public class SimpleTimeClient implements TimeClient
{
    private LocalDateTime dateAndTime;

    public SimpleTimeClient()
    {
        dateAndTime = LocalDateTime.now();
    }

    public void setTime( int hour, int minute, int second )
    {
        LocalDate currentDate = LocalDate.from( dateAndTime );
        LocalTime timeToSet = LocalTime.of( hour, minute, second );
        dateAndTime = LocalDateTime.of( currentDate, timeToSet );
    }

    public void setDate( int day, int month, int year )
    {
        LocalDate dateToSet = LocalDate.of( day, month, year );
        LocalTime currentTime = LocalTime.from( dateAndTime );
        dateAndTime = LocalDateTime.of( dateToSet, currentTime );
    }

    public void setDateAndTime( int day, int month, int year, int hour, int minute, int second )
    {
        LocalDate dateToSet = LocalDate.of( day, month, year );
        LocalTime timeToSet = LocalTime.of( hour, minute, second );
        dateAndTime = LocalDateTime.of( dateToSet, timeToSet );
    }

    public LocalDateTime getLocalDateTime()
    {
        return dateAndTime;
    }

    public String toString()
    {
        return dateAndTime.toString();
    }

    public static void main( String... args )
    {
        TimeClient myTimeClient = new SimpleTimeClient();
        System.out.println( "Testing use of static and default methods in Java 8...");
        System.out.println( "Current time: " + myTimeClient.toString() );
        System.out.println( "Time in California: " + myTimeClient.getZonedDateTime( "Blah blah" ).toString() );
    }
}

Output:

Invalid time zone: Blah blah; using default time zone instead.
Testing use of static and default methods in Java 8...
Current time: 2014-04-03T08:21:56.550
Time in California: 2014-04-03T08:21:56.550-06:00[America/Denver]