How to convert date to string and to date again?
LocalDate.now().toString()
2017-01-23
…and…
LocalDate.parse( "2017-01-23" )
The Question uses troublesome old date-time classes bundled with the earliest versions of Java. Those classes are now legacy, supplanted by the java.time classes built into Java 8, Java 9, and later.
Determining today’s date requires a time zone. For any given moment the date varies around the globe by zone.
If not supplied by you, your JVM’s current default time zone is applied. That default can change at any moment during runtime, and so is unreliable. I suggest you always specify your desired/expected time zone.
ZoneId z = ZoneId.of( "America/Montreal" ) ;
LocalDate ld = LocalDate.now( z ) ;
Your desired format of YYYY-MM-DD happens to comply with the ISO 8601 standard.
That standard happens to be used by default by the java.time classes when parsing/generating strings. So you can simply call LocalDate::parse and LocalDate::toString without specifying a formatting pattern.
String s = ld.toString() ;
To parse:
LocalDate ld = LocalDate.parse( s ) ;
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
Where to obtain the java.time classes?
The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.