How to declare program as public class?

[Winston Luo]

I'm taking an online intro to Java course through my local community college. This is a very beginning Java class, where we turn in assignments through our book publisher's website. The website has its own compiler and for some reason I am getting this error on every project this semester and I can't figure this out.

Here are examples with the compiler error bolded:

[b]FeetToMeters.java:4: error: class feetToMeters is coderanch, should be declared in a file named feetToMeters.java
public class feetToMeters {[/b]
       ^
1 error
1 package ex2_3;
2 
3 import java.util.Scanner;
4 public class feetToMeters {
5 
6 public static void main(String[] args) {
7 Scanner input = new Scanner (System.in); 
8         System.out.println("Enter a value in feet : ");
9         double feet = input.nextDouble();
10         
11         double meter = feet *0.305 ; 
12                System.out.println(feet+ " Feet  is " + meter + "  meter.");
13         
14     }
15 }

[b]
CharCounter.java:3: error: class ProgrammingExercise6_23 is coderanch, should be declared in a file named ProgrammingExercise6_23.java
public class ProgrammingExercise6_23 {[/b]
       ^
1 error
1 import java.util.Scanner;
2  
3 public class ProgrammingExercise6_23 {
4  
5  public static void main(String[] args) {
6   Scanner input = new Scanner(System.in);
7  
8   System.out.print("Enter a string:");
9   String s1 = input.nextLine();
10   System.out.print("Enter a charecter:");
11   char ch = input.nextLine().charAt(0);
12  
13   System.out.println("the number of " + ch + " in the string is "
14     + count(s1, ch));
15  
16  }
17  
18  public static int count(String str, char a) {
19   int count = 0;
20  
21   for (int i = 0; i < str.length(); i++) {
22  
23    if (str.charAt(i) == a)
24     count++;
25  
26   }
27  
28   return count;
29  
30  }
31  
32 }

[b]
SumMajorDiagonal.java:3: error: class ProgramingEx8_2 is coderanch, should be declared in a file named ProgramingEx8_2.java
public class ProgramingEx8_2 {[/b]
       ^
1 error
1 import java.util.Scanner;
2  
3 public class ProgramingEx8_2 {
4  
5  public static void main(String[] args) {
6  
7   double[][] matrix = new double[4][4];
8  
9   java.util.Scanner input = new Scanner(System.in);
10   System.out.println("Enter a 4-by-4 matrix row by row: ");
11   for (int row = 0; row < matrix.length; row++) {
12    for (int column = 0; column < matrix[row].length; column++) {
13     matrix[row][column] = input.nextDouble();
14    }
15   }
16  
17   System.out.println("Sum of the elements in the major diagonal is "
18     + sumMajorDiagonal(matrix));
19  
20  }
21  
22  public static double sumMajorDiagonal(double[][] m) {
23  
24   double sum = 0;
25   for (int row = 0; row < m.length; row++) {
26    sum += m[row][row];
27   }
28   return sum;
29  }
30  
31 }

It seems like I've gotten the rest of the code correctly, but what simple thing am I missing when I "should declare file names for a public class"? If i can fix this, all of my projects for the course will be correct. Please help!

[Ron McLeod]

The messages report that there is a mis-match between the source file name and the public class name

File is named FeetToMeters.java, class is named feetToMeters

File is named CharCounter.java, class is named ProgrammingExercise6_23

File is named SumMajorDiagonal.java, class is named ProgramingEx8_2

[Winston Luo]

So how would I write the code/what modifications would I make so I don't get this message/error?

[Ron McLeod]

Make the name of the file and the public class the same.

For example, change the name of the class in the FeetToMeters.java file to FeetToMeters rather than feetToMeters.

[Liutauras Vilda]

Winston Luo wrote:So how would I write the code/what modifications would I make so I don't get this message/error?

There are some rules you need to remember regarding this.

1. Within one source file there cannot be more than one public class. There can be more classes, but at most one can be coderanch, that means other classes need to be non coderanch.
2. If a class is coderanch, it needs to match its file name in which it is defined.
3. If a class isn't coderanch, name of the file and of the class doesn't need to match.

I may forgot some rules, but these should help you avoid some of the errors.

[Winston Luo]

I still don't understand what I'm doing wrong. Can anyone please just correct the original code I posted in this thread? It's literally just an error with one line...

PLEASE HELP! I'm getting desperate bc the semester is over in a week and this public class error thing for the name of the project code is only thing holding me back from getting it 100 percent correct.

I appreciate the feedback so far but will someone actually run my code through their compiler or just tell me what to fix!?

Again these are the errors that I am getting from the textbook publisher's website for three projects:

1.  (Process a string ) Write a program  that prompts the user to enter a string  and displays its length and its first character .

"StringLength.java:3: error: class ProgrammingEx4_20 is coderanch, should be declared in a file named ProgrammingEx4_20.java
public class ProgrammingEx4_20 {"

for

1 import java.util.Scanner;
2  
3 public class ProgrammingEx4_20 {
4  
5  public static void main(String[] args) {
6   Scanner input = new Scanner(System.in);
7  
8   System.out.print("Enter some string:");
9   String s = input.nextLine();
10   System.out.println("The string length is " + s.length());
11   System.out.println("The first character is " + s.charAt(0));
12  
13  }
14  
15 }

2. Count positive and negative numbers and compute the average of numbers) Write a program  that reads an unspecified number of integers , determines how many positive and negative values  have been read, and computes the total and average of the input values  (not counting zeros). Your program  ends with the input 0. Display the average as a floating-point number.


"AvgWithLoop.java:3: error: class ProgrammingEx5_1 is coderanch, should be declared in a file named ProgrammingEx5_1.java
public class ProgrammingEx5_1 {"

for

1 import java.util.Scanner;
2  
3 public class ProgrammingEx5_1 {
4  
5  public static void main(String[] args) {
6   Scanner input = new Scanner(System.in);
7   System.out.print("Enter an integer, the input ends if it is 0:");
8   int n, countNeg = 0, countPos = 0;
9   float sum = 0;
10  
11   while ((n = input.nextInt()) != 0) {
12    sum = sum + n;
13  
14    if (n > 0) {
15     countPos++;
16    } else if (n < 0) {
17     countNeg++;
18    }
19  
20   }
21  
22   if (countPos + countNeg == 0) {
23    System.out.println("No numbers are entered except 0");
24    System.exit(0);
25   }
26  
27   System.out.println("The number of positives is " + countPos);
28   System.out.println("The number of negatives is " + countNeg);
29   System.out.println("The total is " + sum);
30   System.out.println("The average is " + (sum / (countPos + countNeg)));
31  
32  }
33  
34 }

3. (Occurrences of a specified character ) Write a method  that finds the number of occurrences of a specified character  in a string  using the following header:
public static  int  count(String  str, char  a). Add a main method  to the class  that tests the method  by prompting for a string  and a character , invoking the method  and printing the returned count.

"CharCounter.java:3: error: class ProgrammingExercise6_23 is coderanch, should be declared in a file named ProgrammingExercise6_23.java
public class ProgrammingExercise6_23 {"

for

 import java.util.Scanner;
2  
3 public class ProgrammingExercise6_23 {
4  
5  public static void main(String[] args) {
6   Scanner input = new Scanner(System.in);
7  
8   System.out.print("Enter a string:");
9   String s1 = input.nextLine();
10   System.out.print("Enter a charecter:");
11   char ch = input.nextLine().charAt(0);
12  
13   System.out.println("the number of " + ch + " in the string is "
14     + count(s1, ch));
15  
16  }
17  
18  public static int count(String str, char a) {
19   int count = 0;
20  
21   for (int i = 0; i < str.length(); i++) {
22  
23    if (str.charAt(i) == a)
24     count++;
25  
26   }
27  
28   return count;
29  
30  }
31  
32 }

PLEASE HELP!

[Ron McLeod]

The code seems fine - the problem is that name of the file: StringLength.java does not match the name of the public class: ProgrammingEx4_20.  Have you tried changing either the name of the file or the name of the public class so that they are the same?

I compiled and ran for first project (naming the source file to ProgrammingEx4_20.java) and it ran fine:
    Enter some string:I can't seem to ping the other network
    The string length is 38
    The first character is I

As you mentioned, your compiler is web-based, and without have access to that system it's difficult to provide much more help.

Winston Luo wrote:This is a very beginning Java class, where we turn in assignments through our book publisher's website. The website has its own compiler and for some reason I am getting this error on every project this semester and I can't figure this out.

[Winston Luo]

Thanks for the reponse...could you possibly copy n paste the changes youve made of the code that ran fine? Which lines should i change?

I can't traditionally save the code with a file name because the web based publisher's homework check website just has a box to write code in, submit, and then runs it through their own compiler and verifies whether the code was writtem correctly.

I know I'm asking for a lot but could you directly copy n paste the changes you made in my original code to the forum so I can use that as a model for 8 other projects that all have this 1 stupid error...

[Ron McLeod]

I didn't make any changes to your code - I ran it as-is.  Maybe try renaming your class to match file name mentioned in the error message - from ProgrammingEx4_20 to StringLength

StringLength.java:3: error: class ProgrammingEx4_20 is coderanch, should be declared in a file named ProgrammingEx4_20.java public class ProgrammingEx4_20 {

I'm not sure how I can help you more.  The problem is specific to the system being used to upload and compile the code.  I suggest you contact the school/publisher/website-owner to get support.

I can offer this as an example of what another on-line compiler looks like, and how it needs to be configured/used to compile and run the code for your first project - maybe it will help you understand what you need to do with the system you are trying to use:

[Junilu Lacar]

The rule for Java is that if you have a file named MyClass.java, the only public class that you can declare in it is MyClass, like so:

// MyClass.java

// only one top-level public class allowed in this file and its name must match the source file name
public class MyClass {
   ...
}

The error message you're getting suggests that this is what is happening:

// StringLength.java

// You broke the rule: your public class name DOES NOT match the source file name.
public class ProgrammingEx4_20 {
    ...
}

The error message is technically correct but it's a little misleading as far as telling you exactly what you need to do. However, given these examples, you should be able to figure it out now.

[Jesper de Jong]

Winston Luo wrote:I can't traditionally save the code with a file name because the web based publisher's homework check website just has a box to write code in, submit, and then runs it through their own compiler and verifies whether the code was writtem correctly.

Then you need to rename your class, so that it conforms to what the website expects.

For example, if the website uses the filename CharCounter.java then you should name your class CharCounter, and not ProgrammingExercise6_23.