util.date class methods in Java with Examples

Following are some important date class methods :

1. .toString() : java.util.Date.tostring() method is a java.util.Date class method.It displays the Current date and time.
   Here Date object is converted to a string and represented as:

    day mon dd hh:mm:ss zz yyyy 

   day : day of the week
   mon : month
   dd : day of the month
   hh : hour
   mm : minute
   ss : second
   zz : time zone
   yyyy : year upto 4 decimal places

   Syntax:
   public String toString()
   Return:
   a string representation of the given date.
   

2. .setTime() : java.util.Date.setTime() method is a java.util.Date class method. Sets this Date object to represent a point in time that is time milliseconds after January 1, 1970 00:00:00 GMT.

   Syntax:
   public void setTime(long time)
   Parameters:
   time : the number of milliseconds.
   

3. .hashCode() : java.util.Date.hashCode() method is a java.util.Date class method. Returns a hash code value for the Date object. The result is exclusive OR of the two halves of the primitive long value returned by the getTime() method.

   Syntax:
   public int hashCode()
   Return:
   a hash code value for the Date object.
   

   Java Code to illustrate the use of .toString(), setTime(), hashCode() methods.

   // Java Program explaining util.date class methods//
   // use of .toString(), setTime(), hashCode() methods
   import java.util.*;  // class having access to Date class methods
   
   public class NewClass
   {
       public static void main(String[] args)
       {
           Date mydate = new Date();
   
           // Displaying the current date and time
           System.out.println("System date : "+ mydate.toString() );
   
           // Is used to set time by milliseconds. Adds 15680
           // milliseconds to January 1, 1970 to get new time.
           mydate.setTime(15680);
   
           System.out.println("Time after setting:  " + mydate.toString());
   
           int d = mydate.hashCode();
           System.out.println("Amount (in ms) by which time" +
                              " is shifted :  " + d);
       }
   }

   Output of Java code:

   System date : Tue Nov 01 02:37:18 IST 2016
   Time after setting:  Thu Jan 01 05:30:15 IST 1970
   Amount (in milliseconds)  by which time is shifted :  15680
   

4. .after() : java.util.Date.after() method tests if current date is after the given date.

   Syntax:
   public boolean after(Date d)
   Parameters:
   d : date
   Return:
   true if and only if the instant represented by this Date object is strictly later
   than the instant represented by 'when'; else false
   Exception:
   NullPointerException - if Date object is null.
   

5. .clone() : java.util.Date.clone() method returns the duplicate of passed Date object.

   Syntax:
   public Object clone()
   Return:
   a clone of this instance.
   

6. .before() : java.util.Date.after() method tests if current date is before the given date.

   Syntax:
   public boolean before(Date d)
   Parameters:
   d : date
   Return:
   true if and only if the instant represented by this Date object is strictly earlier
   than the instant represented by 'when'; else false
   Exception:
   NullPointerException - if when is null.
   

Java Code to illustrate the use of after(), clone(), before() methods.

// JAVA program explaining Date class methods
// after(), clone(), before()
import java.util.Date;
public class NewClass
{
    public static void main(String[] args)
    {
        // create 2 dates
        Date date1 = new Date(2016, 11, 18);
        Date date2 = new Date(1997, 10, 27);

        // Use of after() to check date2 is after date1
        boolean a = date2.after(date1);
        System.out.println("Is date2 is after date1 : " + a);

        // Use of after() to check date2 is after date1
        a = date1.after(date2);
        System.out.println("Is date1 is after date2 : " + a);
        System.out.println("");

        // Use of clone() method
        Object date3 = date1.clone();
        System.out.println("Cloned date3 :" + date3.toString());
        System.out.println("");

        // Use of before() to check date2 is after date1
        boolean b = date2.before(date1);
        System.out.println("Is date2 is before date1 : " + a);
    }
}

Output :

Is date2 is after date1 : false
Is date1 is after date2 : true

Cloned date3 :Mon Dec 18 00:00:00 IST 3916

Is date2 is before date1 : true

7. .compareTo() : java.util.Date.compareTo() method compares two dates and results in -1, 0 or 1 based on the comparison.

   Syntax:
   public int compareTo(Date argDate)
   Parameters:
   argDate : another date to compare with
   Result:
   0  : if the argumented date = given date.
   -1 : if the argumented date > given date.
   1  : if the argumented date < given date.
   

8. .equals() : java.util.Date.equals() method checks whether two dates are equal or not based on their millisecond difference.

   Syntax:
   public boolean equals(Object argDate)
   Parameters:
   argDate : another date to compare with
   Result:
   true if both the date are equal; else false.
   

9. .getTime() : java.util.Date.getTime() method results in count of milliseconds of the argumented date, referencing January 1, 1970, 00:00:00 GMT.

   Syntax:
   public long getTime()
   Result:
   milliseconds of the argumented date, referencing January 1, 1970, 00:00:00 GMT.
   

Java Code to illustrate the use of compareTo(), getTime(), equals() methods.

// Java program explaining Date class methods
// compareTo(), getTime(), equals()
import java.util.*;
public class NewClass
{
    public static void main(String[] args)
    {
        Date d1 = new Date(97, 10, 27);
        Date d2 = new Date(97, 6, 12);

        // Use of compareto() method
        int comparison = d1.compareTo(d2);    // d1 > d2
        int comparison2 = d2.compareTo(d1);   // d2 > d1
        int comparison3 = d1.compareTo(d1);   // d1 = d1

        System.out.println("d1 > d2 : " + comparison);
        System.out.println("d1 < d2 : " + comparison2);
        System.out.println("d1 = d1 : " + comparison3);
        System.out.println("");

        // Use of equal() method
        boolean r1 = d1.equals(d2);
        System.out.println("Result of equal() r1 : " + r1);

        boolean r2 = d1.equals(d1);
        System.out.println("Result of equal() r2 : " + r2);
        System.out.println("");


        // Use of getTime() method
        long count1 = d1.getTime();
        long count2 = d1.getTime();
        System.out.println("Milliseconds of d1 : " + count1);
        System.out.println("Milliseconds of d2 : " + count2);
    }
}

Output :

d1 > d2 : 1
d1 < d2 : -1
d1 = d1 : 0

Result of equal() r1 : false
Result of equal() r2 : true

Milliseconds of d1 : 880569000000
Milliseconds of d2 : 880569000000

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