How can I fix this code? I don't understand the error messages.

[Charles Ellis]

Hello,
I have a Leap year assignment that requires that I implement a public class Date and a class named DateJDialog.java.Here is what I wrote:

public class Date
{
	private int day;
	private int month;
	private int year;
	public boolean isLeapYear;
	
	public Date(int d, int m, int y)
	{
		day = d;
		month = m;
		year = y;
	}

	public int daysIs()
	{
		return day;
	}

	public int monthIs()
	{
		return month;
	}

	public int yearIs()
	{
		return year;
	}

	public boolean isLeapYear(int year)
	{
		if (( year % 4 ==0) && year % 100 != 0)
		{
			isLeapYear = true;
		}
		else if ((year % 4 == 0 ) && (year % 100 == 0) && (year % 400 == 0))
		{
			isLeapYear = true;
		}
		else
		{
			isLeapYear = false;
		}
		
		return isLeapYear;
	}
		
}

import javax.swing.JOptionPane;

public class DateJDialog
{
	public static void main(String[] args)
		{	
			String inputString;
			int d;
			int m;
			int y;

			inputString = JOptionPane.showInputDialog("Enter a day as an integer, e.g. 1-31: "); 
			d = Integer.parseInt(inputString);

			inputString = JOptionPane.showInputDialog("Enter a month as an integer, e.g. 1-12: ");
			m = Integer.parseInt(inputString);

			inputString = JOptionPane.showInputDialog("Enter a year ");
			y = Integer.parseInt(inputString);

			Date d = new Date(m,d,y);
			{
				boolean b = d.isLeapYear(y);
			}
			JOptionPane.showMessageDialog(null," If someone said the date " + m + "/" + d + "/" + y + "is a leap year , that statement would be " + b + ".");
			
			System.exit(0);
		}	
}

Date.java compiles correctly. DateJDialog.java gives me the following compliation errors:

DateJDialog.java:21: error: variable d is already defined in method main(String[])
Date d = new Date(m,d,y);
^
DateJDialog.java:23: error: int cannot be dereferenced
boolean b = d.isLeapYear(y);
^
DateJDialog.java:25: error: cannot find symbol
JOptionPane.showMessageDialog(null," If someone said the date " + m + "/" + d + "/" + y + "is a leap year , that statement would be " + b + ".");
^
symbol: variable b
location: class DateJDialog
3 errors

Can anyone help me? I hope I've obeyed the forum rules.

Thanks,
captgbv

[Liutauras Vilda]

Basically it says, that variable "d" is already defined somewhere in your code and you're trying to do so again.
Check carefully your code again. For example (code not intended to do nothing, just an example):

int n = 4;
String s = "four";
String s1 = "four";

if (s.equals(s1)) {
    Integer n = 4; // not allowed, since you have variable "n" initialised on line 1
    n = 4 + 4; // allowed, because you're assigning to a different value
}

[Liutauras Vilda]

Also, when you define variable:

for (int i = 0; i < A.length; i++) {
    // body of your for loop
}
int i = 0;

Variable "i" is initialised within "for" loop on line 1, as well as on line 4. Is this code correct? Why?

What would be if you would try:

for (int i = 0; i < A.length; i++) {
    // body;
}
System.out.println(i);

What would be the output?

I'm referring all code above to your code lines 22, 23, 24, 25 of your DateJdialog class.

And welcome to JavaRanch

[Charles Ellis]

THank you for the quick response. So, how do I fix it? Do I rename the boolean variable?

[Liutauras Vilda]

Charles Ellis wrote:THank you for the quick response. So, how do I fix it? Do I rename the boolean variable?

Always start by fixing 1st error compiler gives you. How to fix, you should try to figure out yourself first. I think I gave you quite accurate examples, so you should be able to work out.
Write down your thoughts, where do you think your problems are? Why do you think these are problems? How would you fix them? And why do you think it should work?

P.S. guesses are not correct way to solve problems.

[Carey Brown]

Charles Ellis wrote:THank you for the quick response. So, how do I fix it? Do I rename the boolean variable?

The problem with your boolean is not the name but that you've declared the variable inside a block ({}) and it goes out of scope (disappears) when you reach the end of the block.
As a general comment I would suggest more descriptive variable names.

[Charles Ellis]

Thank you for your help. I finally see how to fix it. I renamed d to d1 and it fixed it. In the future I will use more descriptive variable names. Thanks again for your help.

[Guillermo Ishi]

Liutauras Vilda wrote:

int n = 4;
String s = "four";
String s1 = "four";

if (s.equals(s1)) {
    Integer n = 4; // not allowed, since you have variable "n" initialised on line 1
    n = 4 + 4; // allowed, because you're assigning to a different value
}

Careful, this is true only if the first n is local (not instance). Also instead of initialized you probably mean instantiated? It doesn't have to be initialized to cause the problem.

[Liutauras Vilda]

Guillermo Ishi wrote:Careful, this is true only if the first n is local (not instance). Also instead of initialized you probably mean instantiated?

1. If "n" were an instance variable, "if" statement couldn't be outside the method.
2. I didn't mean instantiated. I meant what I wrote. But in order to get an error, would be enough to declare without initialisation. But I was right based on my given example.