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Date class is a part of the Utility package and an object of Date class represents the current date and time.






Constructors of Date class




Constructor	Description
Date()	This constructor creates a Date object with represents the current date and time.
Date(long milliseconds)	This constructor creates a Date object with represents the milliseconds passed since January 1,1970.








Methods of Date class




Methods	Description
boolean before(Date date)	This method returns true if the invoked Date object represents a date before than the specified date.
boolean after(Date date)	This method returns true if the invoked Date object represents a date after than the specified date.
int compareTo(Date date)	Returns a zero if the invoking Date object represents the same date as date. Returns a positive value if invoking Date object represents a date later than the date. Returns a negative value if invoking Date object represents a date earlier than the date
boolean equals(Object date)	This method returns true the invoked Date object represents the same date as date.
long getTime()	This method returns number of milliseconds passed since January 1,1970.
void setTime(long milliseconds)	This method sets the invoked Date object's date as per milliseconds passed to this method.
String toString()	This method converts the Date object to String value.








A simple example of Date class.




//program when scanner class reads through the keyboard.

import java.util.*;

class A
{
public static void main(String... ar)
{
Date d1 = new Date();
System.out.println(d1);

Date d2 = new Date(1000000000l);
System.out.println(d2);
}
}





Output




Mon Jul 24 17:01:12 IST 2017
Mon Jan 12 19:16:40 IST 1970





Program Analysis


In the preceding code, we have created two objects of Date class each using a different constructor -:
• The first object of Date class is constructed using a constructor that doesn't accept any argument. This date object represents the current date and time.
• The second object of Date class is constructed using a different constructor that takes milliseconds passed since January 1, 1970 to construct the Date object.





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Checking if a date is later or before than a particular date.




import java.util.*;

class A
{
public static void main(String... ar)
{
Date d1 = new Date();
System.out.println("Date 1 : "+ d1);

Date d2 = new Date(1000000000l);
System.out.println("Date 2 : "+ d2);


System.out.println("Is Date 1 before Date 2? : " + d1.before(d2));
System.out.println("Is Date 1 after Date 2? : " + d1.after(d2));
}
}





Output -




Date 1 : Mon Jul 24 17:20:01 IST 2017
Date 2 : Mon Jan 12 19:16:40 IST 1970
Is Date 1 before Date 2? : false
Is Date 1 after Date 2? : true





Program Analysis


In the last code, we have constructed two Date objects and we are checking if an invoking date object is represents a Date before or after the Date object passed at an argument to after(Date date) and before(Date date) methods. Note :Methods after(Date date) and before(Date date) returns a boolean value.






Another way to compare the two dates using compareTo() method.


In the next code we are going to compare the two days represented by two Date objects using compareTo() method.



import java.util.*;

class A
{
public static void main(String... ar)
{
Date d1 = new Date();
System.out.println("Date1 : "+ d1);

Date d2 = new Date(1000000000l);
System.out.println("Date2 : "+ d2);


Date d3 = new Date(1000000000l);
System.out.println("Date3 : "+ d3);

System.out.println("Comparing Date1 with Date2 : "+ d1.compareTo(d2));
System.out.println("Comparing Date2 with Date1 : "+ d2.compareTo(d1));
System.out.println("Comparing Date2 with Date3 : "+ d2.compareTo(d3));
}
}





Output -




Date1 : Mon Jul 24 17:21:40 IST 2017
Date2 : Mon Jan 12 19:16:40 IST 1970
Date3 : Mon Jan 12 19:16:40 IST 1970
Comparing Date1 with Date2 : 1
Comparing Date2 with Date1 : -1
Comparing Date2 with Date3 : 0





Program Analysis


We have compared Date objects with each other using compareTo() method -
• Firstly, Date1 is compared with Date2, as the date represented by Date1 object is later than the date represented by Date2 object, hence 1 is returned.
• Secondly, Date2 is compared with Date1, as the date represented by Date2 object is earlier than the date represented by Date2 object, hence -1 is returned.
• Finally, Date2 is compared with Date3, as the date represented by Date2 object is equal to the date represented by Date3 object, hence 0 is returned.







Getting and setting(modifying) the date.

//Getting and Setting(modifying) the date

import java.util.*;

class A
{
public static void main(String... ar)
{
Date d1 = new Date();
System.out.println("Date1 : "+ d1);

Date d2 = new Date(1000000000l);
System.out.println("Date2 : "+ d2);


Date d3 = new Date(1000000000l);
System.out.println("Date3 : "+ d3);


System.out.println("Converting Date1 to Number of milliseconds since January 1, 1970 : " + d1.getTime());
System.out.println("Converting Date2 to Number of milliseconds since January 1, 1970 : " + d2.getTime());
System.out.println("Converting Date3 to Number of milliseconds since January 1, 1970 : " + d3.getTime());

d1.setTime(9999999999l);
d2.setTime(5000000000l);
d3.setTime(2222222222l);

System.out.println("Modified Date1 : "+ d1);
System.out.println("Modified Date2 : "+ d2);
System.out.println("Modified Date3 : "+ d3);
}
}

Output -

Date1 : Mon Jul 24 17:23:10 IST 2017
Date2 : Mon Jan 12 19:16:40 IST 1970
Date3 : Mon Jan 12 19:16:40 IST 1970
Converting Date1 to Number of milliseconds since January 1, 1970 : 1500897190947
Converting Date2 to Number of milliseconds since January 1, 1970 : 1000000000
Converting Date3 to Number of milliseconds since January 1, 1970 : 1000000000
Modified Date1 : Sun Apr 26 23:16:39 IST 1970
Modified Date2 : Sat Feb 28 02:23:20 IST 1970
Modified Date3 : Mon Jan 26 22:47:02 IST 1970

Program Analysis

• At first we have created three date objects
• Secondly, we have extracted a date out of each Date object using getTime() method.
• Finally, we have modified the date contained in the Date object using setTime() method by passing it a new date in the form of milliseconds passed since January 1, 1970 using setTime() method.

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