Date class in Java

The Date class of java. util package implements Serializable, Cloneable, and Comparable interface. It provides constructors and methods to deal with date and time with java. Date(): Creates date object representing the current java date and time.

Parameter	Explanation
No parameter	Creates a new Date object using the allocation time (to the nearest millisecond)
long date	Creates a new Date object with the time set to the number of milliseconds since “the epoch” (January 1, 1970, 00:00:00 GMT)

Convert java.util.Date to java.sql.Date

“java.util.Date” to “java.sql.Date” conversion is usually necessary when a Date object needs to be written in a database.

java.sql.Date is a wrapper around millisecond value and is used by JDBC to identify an SQL DATE type

In the below example, we use the java.util.Date() constructor, that creates a Date object and initializes it to represent time to the nearest millisecond. This data is used in the convert(java.util.Date utilDate) method to return a java.sql.Date object

Example

public class UtilToSqlConversion {
    public static void main(String args[])
    {
        java.util.Date utilDate = new java.util.Date();
        System.out.println("java.util.Date is : " + utilDate);
        java.sql.Date sqlDate = convert(utilDate);
        System.out.println("java.sql.Date is : " + sqlDate);
        DateFormat df = new SimpleDateFormat("dd/MM/YYYY - hh:mm:ss");
       System.out.println("dateFormated date is : " + df.format(utilDate));
   }
   private static java.sql.Date convert(java.util.Date uDate) {
      java.sql.Date sDate = new java.sql.Date(uDate.getTime());
return sDate;
   }
}

Output

java.util.Date is : Fri Jul 22 14:40:35 IST 2016
java.sql.Date is : 2016-07-22
dateFormated date is : 22/07/2016 - 02:40:35

java.util.Date has both date and time information, whereas java.sql.Date only has date information

A basic date output

Using the following code with the format string yyyy/MM/dd hh:mm.ss, we will receive the following output

2016/04/19 11:45.36

// define the format to use
String formatString = "yyyy/MM/dd hh:mm.ss";

// get a current date object
Date date = Calendar.getInstance().getTime();

// create the formatter
SimpleDateFormat simpleDateFormat = new SimpleDateFormat(formatString);

// format the date
String formattedDate = simpleDateFormat.format(date);

// print it
System.out.println(formattedDate);

// single-line version of all above code
System.out.println(new SimpleDateFormat("yyyy/MM/dd
hh:mm.ss").format(Calendar.getInstance().getTime()));

Java 8 LocalDate and LocalDateTime objects

Date and LocalDate objects can not be compared exactly to each other because a Date object represents both a particular day and date, while a LocalDate object does not contain information about time or time zone. Yet switching between the two can be helpful if you only think about the actual date information and not the time information.

Creates a LocalDate

// Create a default date
LocalDate lDate = LocalDate.now();

// Creates a date from values
lDate = LocalDate.of(2017, 12, 15);

// create a date from string
lDate = LocalDate.parse("2017-12-15");

// creates a date from zone
LocalDate.now(ZoneId.systemDefault());

Creates a LocalDateTime

// Create a default date time
LocalDateTime lDateTime = LocalDateTime.now();

// Creates a date time from values
lDateTime = LocalDateTime.of(2017, 12, 15, 11, 30);

// create a date time from string
lDateTime = LocalDateTime.parse("2017-12-05T11:30:30");

// create a date time from zone
LocalDateTime.now(ZoneId.systemDefault());

LocalDate to Date and vice-versa

Date date = Date.from(Instant.now());
ZoneId defaultZoneId = ZoneId.systemDefault();

// Date to LocalDate
LocalDate localDate = date.toInstant().atZone(defaultZoneId).toLocalDate();

// LocalDate to Date
Date.from(localDate.atStartOfDay(defaultZoneId).toInstant());

LocalDateTime to Date and vice-versa

Date date = Date.from(Instant.now());
ZoneId defaultZoneId = ZoneId.systemDefault();
// Date to LocalDateTime
LocalDateTime localDateTime = date.toInstant().atZone(defaultZoneId).toLocalDateTime();

// LocalDateTime to Date
Date out = Date.from(localDateTime.atZone(defaultZoneId).toInstant());