Calendar.Month 给出错误的输出

Question

I have been using java.util for all date and calendar representations. But I am facing a strange problem here. Calendar.MONTH , Calendar.DAY_OF_MONTH , etc all give wrong outputs. But when I use Calendar.getTime() , I get the right output. What might be the problem?

public class TestClass {

    public static void main(String[] args) {
        Calendar rightNow = Calendar.getInstance();
        System.out.println(rightNow.MONTH);
        System.out.println(rightNow.DAY_OF_MONTH);
        System.out.println(rightNow.YEAR);
        System.out.println(rightNow.getTime());
    }
}

And the output for the same is:

2
5
1
Tue Jan 22 10:31:44 GMT+05:30 2013

Answer 1

    System.out.println(rightNow.MONTH);
    System.out.println(rightNow.DAY_OF_MONTH);
    System.out.println(rightNow.YEAR);
    System.out.println(rightNow.getTime());

You are printing Calendar constant values.

If you want values, you need to do get....

Example:

    System.out.println(rightNow.get(Calendar.MONTH));

Read Calendar javadoc for more information.

Answer 2

Calendar.MONTH doesn't return the current month. It is a constant whose value is 2.

From the source:

public final static int MONTH = 2;

It is for use as a parameter in Calendar's get method

public int get(int field) {...}

The design of Calendar is from the early days of Java, when many of today's conventions were different, non-existant, or developing. Oracle (and earlier, Sun), would never let an API like the java.util.Calendar API become part of the standard API today.

And, for completeness, use Joda Time instead of Java's Date and Calendar API's.

Answer 3

java.time

    ZonedDateTime rightNow = ZonedDateTime.now(ZoneId.of("Africa/Cairo"));
    System.out.println(rightNow.getMonth());
    System.out.println(rightNow.getMonthValue());
    System.out.println(rightNow.getDayOfMonth());
    System.out.println(rightNow.getYear());
    System.out.println(rightNow);

Output when running just now was:

 FEBRUARY 2 15 2019 2019-02-15T21:15:06.313809+02:00[Africa/Cairo]

Don't use Calendar

The Calendar class is confusing and suffers from poor design, so no wonder that you're wondering. Fortunately it was replaced the year after you asked this quesion by ZonedDateTime and other classes in java.time, the modern Java date and time API. So never use Calendar again now.

The Calendar class was trying to be very general, so instead of a getMonth method, etc., it had the notion of fields that could be read and set. Since it was designed long before Java had enum s, each field had a number and a named constant for that number. So YEAR (of era) was 1, MONTH was 2, etc. To get the value of the field of a Calendar object you were supposed to call the get method passing the appropriate named constant, for example rightNow.get(Calendar.MONTH) . Using just rightNow.MONTH is a regularly repeated mistake. It just gives you the value of the constant, 2.

Link

Oracle tutorial: Date Time explaining how to use java.time.

Answer 4

    Calendar now = Calendar.getInstance();
    out.println("month now= " + (now.get(Calendar.MONTH)+1));

OR with GregorianCalender:

    GregorianCalendar nu  = new GregorianCalendar();
    int day = nu.get(Calendar.DAY_OF_MONTH);
    int month = (nu.get(Calendar.MONTH)+1);  //month +1 because january`==0
    int year= nu.get(Calendar.YEAR);
    int hour= nu.get(Calendar.HOUR_OF_DAY);
    int minutes= nu.get(Calendar.MINUTE);

here