Calendar Class

It is a predefined class in java.util package.it is used to get date and time along with other internal time and date properties of Calendar.
The main difference between date and Calendar class is date always represents current system date and time. Where as Calendar class can be used to get the date ,time and other properties in a complete Calendar year(from january to december).
Syntax:
Calendar c=Calendar.getInstance();
In the above syntax getInstance() is a predefined method of a Calendar class.Which returns Calendar class object.

Key Points

What is Calendar Class

import java.util.*;
public class Main {
public static void main(String[] args) {
Calendar c1=Calendar.getInstance();
System.out.println("Current date");
int dd=c1.get(Calendar.DATE);
int mm=c1.get(Calendar.MONTH);
mm++;
int yy=c1.get(Calendar.YEAR);
System.out.println(dd+"-"+mm+"-"+yy);
System.out.println("Current Time");
int h=c1.get(Calendar.HOUR);
int m=c1.get(Calendar.MINUTE);
int s=c1.get(Calendar.SECOND);
System.out.println(h+":"+m+":"+s);
int x=c1.get(Calendar.AM_PM);
if(x==0)
{
System.out.println("AM");
System.out.println("Good Morning");
}
else
{
System.out.println("PM");
System.out.println("Good Evening");
}
int dw=c1.get(Calendar.DAY_OF_YEAR);
System.out.println(dw);
}
}

Output:

Current date
26-5-2022
Current Time
8:40:50
PM
Good Evening
269

Addition Program:Please execute a program in a particular time and date

Program
Online Compiler

import java.util.*;
public class Main {
public static void main(String[] args) {
Calendar c1=Calendar.getInstance();
System.out.println("Current date");
int dd=c1.get(Calendar.DATE);
int mm=c1.get(Calendar.MONTH);
mm++;
int yy=c1.get(Calendar.YEAR);
System.out.println(dd+"-"+mm+"-"+yy);
System.out.println("Current Time");
int h=c1.get(Calendar.HOUR);
int m=c1.get(Calendar.MINUTE);
int s=c1.get(Calendar.SECOND);
System.out.println(h+":"+m+":"+s);
int x=c1.get(Calendar.AM_PM);
int p,q,r;
Scanner ss=new Scanner(System.in);
if(dd==28 && mm==9 && yy==2022 && h>12 && m>10 && s>0)
{
System.out.println("Enter p,q values");
p=ss.nextInt();
q=ss.nextInt();
r=p+q;
}
else
{
System.out.println("Please execute some other time");
}
}
}

Output:

Current date
27-9-2022
Current Time
11:6:21
Please execute some other time