How to do leap year in java

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(Date Class) Create a class called Date that includes three instance variables—a month (type int), a day (type int), and a year (type int), the initial value of the date is 1/1/1970. Provide a set and a get method for each instance variable. Validate the year to be between 1-3000, validate
the month and the day, and Provide a method displayDate that displays the month, day and year separated by forward slashes (/). Write a test app named DateTest that demonstrates class Date’s capabilities. Write a testing class. Also find the leap year whether there are 28 or 29 days in a month using switch case.

What I have tried:

Java

public class Date {
	int month=1;
	int day=1;
	int year=1970;
	
	void setMonth(int m) {
		if (m>=1 && m<=12)
			month=m;
	}
	
	void setDay(int d) {
			switch(month) {
			case 1: case 3: case 5: case 7: case 8: case 10: case 12:
				if (d<=31) {
					day=d;
					break;
				}
				
			case 4: case 6: case 9: case 11:
				if (d<=30) {
					day=d;
					break;
				}
				//System.out.println();//sysout
				

//This part isn't working which is the leap year part. When I try putting 29 //in February of a leap year such as 2002 it shows 29/2/2002 which is wrong //as there is only 28 days in February of 2002.

			case 2:
				if ((year%400==0) || ((year % 4 ==0) && (year %100!=0)) &&  day<=29){
					day=d;
					break; 
				}
				
				else{
					if (day<=28) {
						day=d;
						break; 
					}
				}
					
			}
	}
		

	
	void setYear(int y) {
		if (y>=1 && y<=3000)
			year=y;
	}
	
	int getMonth() {
		return month;
	}
	
	int getDay() {
		return day;
	}
	
	int getYear() {
		return year;
	}
	
	void DisplayDate() {
		System.out.print(getDay()+"/"+getMonth()+"/"+getYear());
	}
}

Posted 18-Sep-22 21:04pm

Cloverr

Updated 19-Sep-22 21:35pm

Patrice T

v5

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CPallini 19-Sep-22 3:10am

And what is the problem with your code (other than you only check for day > 1 on leap february, and this check is also wrong) ?

Cloverr 20-Sep-22 3:02am

the leap year part, if and else isn't working

Richard MacCutchan 19-Sep-22 4:34am

You do not take any action in your setters if the values are out of range. You should either display a message or throw an exception.

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OriginalGriff · Answer 1 · 2022-09-18T21:13:00

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

Java

int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

CPallini · Answer 2 · 2022-09-19T21:35:00

Quote:
the leap year part, if and else isn't working

Nope, the leap year test is correct.

However you should take care to re-check the date every time a setter is called. For instance, if you set the day 29 when the year is 2000 and the month is 2, it is fine. Yet, if you later change the year (say to 2017) the you have to check again all the variables, since 29 Feb 2017 is not allowed.

How to do leap year in java

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