orry kaplan

Henry Wong wrote:What version of Java are you using?

Build id: 20100617-1415

public static boolean LeapYear() { System.out.println("LEAP YEAR - Enter the year: "); while (!input.hasNextInt()) { System.out.println("Invalid input. Please enter a year: ");        input.next();    } int Year = input.nextInt(); while (Year < 1582) { System.out.println("Invalid input. Please enter a year: "); while (!input.hasNextInt()) { System.out.println("Invalid input. Please enter the year: ");        input.next();    } Year = input.nextInt();    }        if ((Year % 4 == 0) && Year % 100 != 0)        {         return (true);        }        else if ((Year % 4 == 0) && (Year % 100 == 0) && (Year % 400 == 0))        {         return (true);        }        else        {         return (false);        } } public static int DaysMonth() { System.out.println("DAYS IN A MONTH - Enter the Month: "); String Month = input.next(); System.out.println("DAYS IN A MONTH - Enter the Year: "); while (!input.hasNextInt()) { System.out.println("Invalid input. Please enter the year: ");        input.next();    } int Year = input.nextInt(); while (Year < 1582) { System.out.println("Invalid input. Please enter a year: "); Year = input.nextInt();    } int Days = 0; boolean LeapYear;        if ((Year % 4 == 0) && Year % 100 != 0)        {         LeapYear = true;        }        else if ((Year % 4 == 0) && (Year % 100 == 0) && (Year % 400 == 0))        {         LeapYear = true;        }        else        {         LeapYear = false;        }        switch (Month)        {        case "January":         Days = 31;         break;        case "February":         if(LeapYear == true)         Days = 29;         else         Days = 28;         break;        case "March":         Days = 31;         break;        case "April":         Days = 30;         break;        case "May":         Days = 31;         break;        case "June":         Days = 30;         break;        case "July":         Days = 31;         break;        case "August":         Days = 31;         break;        case "September":         Days = 30;         break;        case "October":         Days = 31;         break;        case "November":         Days = 30;         break;        case "December":         Days = 31;         break;        case "Default":         Days = 0;         break;        }                System.out.println("The number of days on " + Month + " " + Year + " is: ");        return Days; }

I have Month; written in the switch statement above but i'm getting a error saying "Cannot switch on a value of type String. Only convertible int values or enum constants are permitted".
what does this mean? can anyone help?

Henry Wong wrote:
When you try to print any object, that is not a string, the println() method will call the toString() method of the object, in order to get the string representation, so that it can print it.

Since your Data class, did not implement the toString() method, it will inherit it from its super class. And with the Object class, the toString() method returns the name of the class along with the Identity hash for the instance.

Henry

Would this be more appropriate?

for(int i = 0; i < list.size(); ++i) { System.out.println(list.get(i).GetName()+", "+list.get(i).GetAge()); } System.out.println(Arrays.toString(list));     System.out.println("");

i have my code here but whenever i print, a part of the print is showing up in an unreadable format. any help as to what i need to do?

import java.util.ArrayList; import java.util.Arrays; public class Lab { public static void main(String args[]) { Data x = new Data("Fred",21); Data p = new Data("Jo",43); Data r = new Data("Harry",78); Data o = new Data("Zoe",37); ArrayList<Data> list = new ArrayList<Data>(); list.add(x);        list.add(p);        list.add(r); list.add(o); for(int i = 0; i < list.size(); ++i) { System.out.println(list.get(i).GetName()+" "+list.get(i).GetAge()); } System.out.println(list.toString());        System.out.println("");

prints:

Fred 21
Jo 43
Harry 78
Zoe 37
[Data@1540e19d, Data@677327b6, Data@14ae5a5, Data@7f31245a]

Dave Tolls wrote:

orry kaplan wrote:[
This is all of the code i have.

How can this be all the code?
There isn't even a class definition.

import java.util.Arrays; public class Lab { public static void main(String args[]) { Data x = new Data("Fred",21); x.Print(); Data p = new Data("Jo",43); p.Print(); Data o = new Data("Zoe",37); o.Print(); System.out.println(""); ArrayList<Data> list = new ArrayList<Data>(); list.add(x);        list.add(p); list.add(o); for(int i = 0; i < list.size(); i++) { System.out.println(list.get(i).GetName()+" "+list.get(i).GetAge()); System.out.println(""); //Part 2 public void method(String[] PrintDataArray) { System.out.println(Arrays.toString((PrintDataArray)));   } ArrayList ArrayA = new ArrayList(); ArrayA.method(new String[]{}); ArrayList<Data> ArrayA = new ArrayList<Data>(); list.add(x);    list.add(p); list.add(o); ArrayList<Data> ArrayB = new ArrayList<>(); PrintDataArray(ArrayA); System.out.println(); ArrayB = ArrayA; PrintDataArray(ArrayB); System.out.println(); ArrayA.remove(1); PrintDataArray(ArrayB); }  } }

Carey Brown wrote:

orry kaplan wrote:This is all of the code i have. And my error message i got is, " The method PrintDataArray(ArrayList<Data>) is undefined for the type PJ1"

What is PJ1 ?

Thats just the name of the project. Do you know what the problem is and how i can possibly fix it?

Carey Brown wrote:2 things would help us help you: 1) show all of your code, 2) copy-n-paste error message(s) into your post.

PrintDataArray(ArrayA);

Do you have such a method? What argument is the method expecting?

This is all of the code i have. And my error message i got is, " The method PrintDataArray(ArrayList<Data>) is undefined for the type PJ1"

Ole Sandum wrote:Not using the wrapper classes, no. But it is possible the paper used the primitive types long and float (lowercase l and f), which can be converted between eachother. Are you sure you quoted the paper directly without changing the case of those letters?

100% quoted correctly, however it does say what happenes when F and L are removed however that should still present an invalid answer?

hi, i am trying to print these arrays however it is coming up with an error on one part (listed below)

Data x = new Data("Fred",21); x.Print(); Data p = new Data("Jo",43); p.Print(); Data o = new Data("Zoe",37); o.Print(); for(int i = 0; i < list.size(); i++) { System.out.println(list.get(i).GetName()+" "+list.get(i).GetAge()); ArrayList<Data> ArrayA = new ArrayList<Data>(); list.add(x);    list.add(p); list.add(o); ArrayList<Data> ArrayB = new ArrayList<>(); PrintDataArray(ArrayA);   (ERROR ON PrintDataArray) for all 3 rows System.out.println(); ArrayB = ArrayA; PrintDataArray(ArrayB); System.out.println(); ArrayA.remove(1); PrintDataArray(ArrayB);


I am sooo confused as to why this is showing, any help?

Ole Sandum wrote:Here you are trying to cast a reference of type Long to Float.

Note that to be able to successfully cast a reference to a type T, the object referred to by said variable must be of a subtype of T (or of T itself). The compiler is clever enough to see that this will never be the case for Float and Long, and does not allow the code to compile.

So basically it cannot be done?

Ole Sandum wrote:Hi, orry.

Primitives cannot be cast the same way reference variables can. Maybe you are talking about primitive type conversion? Or maybe you are trying to cast between the wrapper types Float and Long?

If you are trying to do the latter, that is impossible because none of those two classes inherits from the other.

Maybe it would help if you showed us some code showcasing the problem?

Well im working on some past papers and this question came up:

Long v1 = 10L;
Float v2 = 10.3F;

Observe what happens when you remove the L and F. Rewrite these lines using casting.


so so far i put this but no luck due to it saying they cannot be casted:

Long v1 = 10L; Float v2 = (Float)v1;

I am trying to cast a float to a long or a long to a float but every time java says i cannot cast them either way i try. Can they be casted?

Carey Brown wrote:Yep. That should work.

Do you need to print age as well?

Yeah I do but I wasn't sure how to add it in too, unless I duplicate the print line with GetName and change the second one to GetAge?

Carey Brown wrote:

Carey Brown wrote:You could have been extremely verbose like this:
for( Data data : arr ) {        System.out.print(("("+data.GetName()));        System.out.print(",");        System.out.print(data.GetAge());        System.out.println(") "); }

In your case, because you have a print() method, you could have done this:
for( Data data : arr )    data.print();
However, you COULD NOT have done this without a toString():
System.println( arr );

import java.util.ArrayList; import java.util.Arrays; public class CS1702_Lab5 { public static void main(String args[]) { Data x = new Data("Fred",21); x.Print(); Data p = new Data("Jo",43); p.Print(); Data o = new Data("Zoe",37); o.Print(); System.out.println(""); ArrayList<Data> list = new ArrayList<Data>(); list.add(x);    list.add(p); list.add(o); for(int i = 0; i < list.size(); i++) {        System.out.println(list.get(i).GetName()); } } }

i have finalised this thinking i have finished the problem. do you think this seems correct?

Carey Brown wrote:

orry kaplan wrote:That code snip you put above, is that the solution to this? because even though i get that it cannot be printed unless it is toString, is there a way to print this list in a readable format without it as it seems a little confusing to use all the time.

Using toString() is considered the proper way to do it. You could have been extremely verbose like this:
for( Data data : arr ) {        System.out.print(("("+data.GetName()));        System.out.print(",");        System.out.print(data.GetAge());        System.out.println(") "); }
This is not the path usually chosen because of the risks of errors being introduced during maintenance and modification. Also, toString() is quite often used during the debugging stage of development.

Note that inserting parenthesis, commas, field names (e.g. "Name:") into the String are all up to the designer. Whatever you need for meaningful output.

/
So can the toString be used on this program effectively