Reading From File Question??

[kraigballa]

My code is below (it works)...however, I am wondering how to put this in a try/catch? For instance, if the file cannot be found, or problems with reading data throw exception. Also I'm kind of new to Java and I can't figure out how to ask the user for the filename and then use Scanner to read from that file...

public class ProcessScores {
	
	public static void main (String args[]) throws FileNotFoundException	{
		Scanner inFile = new Scanner(new FileReader ("scores.txt"));
        int counter = 0; // Keep track of how many integers are in the file
        double sum = 0; 
        
        while(inFile.hasNextInt())	{
            counter++;
            inFile.nextInt();
        }
        Scanner inFile2 = new Scanner(new FileReader ("scores.txt"));
        int scoresArray[] = new int[counter];
        for(int i=0;i<counter;i++)	{
            scoresArray[i]=inFile2.nextInt(); //fill the array with the integers
            sum += scoresArray[i];
        }
        
        Arrays.sort(scoresArray);
        
        letterGrades(scoresArray, counter);
        average(sum, counter);

	}
	
	public static void average (double sum, int counter)	{
		DecimalFormat format = new DecimalFormat();
        format.setMaximumFractionDigits(2);
        System.out.println("\nThe average test score is: " + format.format(sum/counter));
	}
	
	public static void letterGrades(int[] scores, int counter){
		System.out.println("Score\tLetter Grade");
		System.out.println("------------------------------");
		
		for(int i=0;i<counter;i++)	{
			if (scores[i] <= 100 && scores[i] > 89)
				System.out.println(scores[i] +"\t\tA");
			else if (scores[i] <= 89 && scores[i] > 79)
			System.out.println(scores[i] +"\t\tB");
			else if (scores[i] <= 79 && scores[i] > 69)
				System.out.println(scores[i] +"\t\tC");
			else if (scores[i] <= 69 && scores[i] > 59)
				System.out.println(scores[i] +"\t\tD");
			else if (scores[i] <= 59 && scores[i] >= 0)
				System.out.println(scores[i] +"\t\tF");
		}
		System.out.println("------------------------------");
	}
}

Here's sample file:

79  86  97  82  90  89
68 72 87 78 
95 
99

Also how would I go about it if the file didn't have just ints? Like...

79  86  97  82  Bob 90  89
68 72 87 78 ffff 95 
99 dodo

[Norm]

how to put this in a try/catch?

A try{}catch is sort of like an if else with the code inside of the try{} being the condition for the if.
If there are no exceptions thrown the catch block is not executed. If there is an exception it is thrown:
if(this code executes with no exception) {
// continue below
}else { // if there is an exception
// do the code in the catch block here
}
The two paths through the above if statement will both continue here

You put the try{} around the code that can have an exception.

What do you want the code to do when there is an exception? Skip the number or exit the program or ???

[kraigballa]

I would want it to skip and go on to the next. Also how would it go if I were going to ask the user what the name of the file is? I would want to make sure they enter in a filename that is available??

[Norm]

make sure they enter in a filename that is available?

See the File class. It can test if a file exists.

[kraigballa]

Do you know of a good example somewhere that shows how to grab the input from the user in order to read that file??

[Norm]

You could use the Scanner class to get input from a user. There are lots of code examples on this forum.

[kraigballa]

What do you want the code to do when there is an exception? Skip the number or exit the program or ???

Let's say the user input a correct file...the file has letters in it, but I only want the numbers. How do I continue to scan the file even after string/char is found? For instance...

79  86  97  82  90  89
68 72 87 78 95 99 
100 10 ff
12 13

[Norm]

How do I continue to scan the file even after string/char is found?

It depends on what class and methods you are using to read the file.
If you read an invalid token/word from the file, ignore it and go back and read the next token/word.
pseudo code:
begin loop
read token
if token is invalid continue back to the top of the loop to read the next token
process the token
end of loop

[kraigballa]

I am using

  Scanner inFile2 = new Scanner(new FileReader (fName));
	        int scoresArray[] = new int[counter];
	        for(int i=0;i<counter;i++)	{
	            scoresArray[i]=inFile2.nextInt(); // Fill the array with the integers
	            sum += scoresArray[i];
	        }

How would you loop to read the next token without adding it to the array? Right now if the file has anything other than an int it completely stops reading the file and exits displaying what it did read..up until the invalid token.

[Norm]

How would you loop to read the next token without adding it to the array?

By doing it in several steps:
read the next token into a temp variable
validate it
add it to array

To keep control of the file input method calls, you need to put them in a try{}catch block.

[kraigballa]

What else would I need to do for lines 13-16??

try	{
			Scanner inFile = new Scanner(new FileReader (fName));
	        
	        while(inFile.hasNextInt())	{
	            counter++;
	            inFile.nextInt();
	        }
	        
	        Scanner inFile2 = new Scanner(new FileReader (fName));
	        int scoresArray[] = new int[counter];
	        for(int i=0;i<counter;i++)	{
	        	
	        	if(inFile2.next() != int){ // What do I need to put for int??
	        		Exception problem = new Exception("Value is not an int");
	        		throw problem;
	        		... // How do you make it continue through the file after exception?
	        	}
	            scoresArray[i]=inFile2.nextInt(); // Fill the array with the integers
	            sum += scoresArray[i];
	        }
        
	        Arrays.sort(scoresArray);
	        letterGrades(scoresArray, counter);
	        average(sum, counter);
		}
		catch (FileNotFoundException e)	{
			System.out.println(fName + ": could not be found.");
		}

[Norm]

What else would I need to do for lines 13-16??

What are you trying to do on those lines?
If you want to test if a String is a valid integer, use the Integer parse int method. It will throw an exception if the String does not contain a valid number.

[kraigballa]

Ok I did the following...and when it gets to anything not an int it stops. However, I want it to skip that token and continue to the next.

 Scanner inFile2 = new Scanner(new FileReader (fName));
	        int scoresArray[] = new int[counter];
	        String tempArray[] = new String[counter];
	        for(int i=0;i<counter;i++)	{
	        	
	            tempArray[i]=inFile2.next(); // Fill the array
	            scoresArray[i] = Integer.parseInt(tempArray[i]);
	            sum += scoresArray[i];
	        }

[Norm]

Back in post #10 I suggested the steps to take.
1) read the token into a temp variable not an array.

You need to put the parseInt call inside of a try{} catch block. If the number is invalid, parseInt throws an exception.

[kraigballa]

Ok this is what I did... temp is a string now

try	{
			Scanner inFile = new Scanner(new FileReader (fName));
	        
	        while(inFile.hasNext())	{
	            counter++;
	            inFile.next();
	        }
	        
	        Scanner inFile2 = new Scanner(new FileReader (fName));
	        int scoresArray[] = new int[counter];
	        for(int i=0;i<counter;i++)	{
	        	
	            temp=inFile2.next(); // Fill the array with the integers

	            scoresArray[i] = Integer.parseInt(temp);
	            sum += scoresArray[i];
	            //System.out.println(temp);
	        }
        
	        Arrays.sort(scoresArray);
	        letterGrades(scoresArray, counter);
	        average(sum, counter);
		}
		catch (FileNotFoundException e)	{
			System.out.println(fName + ": could not be found.");
		}
		catch(NumberFormatException e) {
		    System.out.println("Not an Integer");
		}

Now when the file has letters I get the Exception "Not an Integer". If the files has anything that is not an integer I just want to skip it and move on until the end of the file. I'm not sure how to validate that??

[Norm]

I get the Exception

Yes that is what you expect when nextInt reads bad data. You need to put the call to parseInt() inside of a try catch block.
Use the continue statement to go back to the next() call
See post#2 again.

how to validate that??

The thrown exception says the value read was invalid.

[diamonddragon]

What are you trying to do on those lines?
If you want to test if a String is a valid integer, use the Integer parse int method. It will throw an exception if the String does not contain a valid number.

Or maybe something like this:

String temp = input.next();
if (temp.matches("[\\d]*"))
   (something with temp)

[kraigballa]

What does the temp.matches("[\\d]*") do??

[diamonddragon]

What does the temp.matches("[\\d]*") do??

Validate if temp(next complete token) is only od digits.

[kraigballa]

I tried that and now I get

  if(temp.matches("[\\d]*")){
	            	scoresArray[i] = Integer.parseInt(temp);
	            }else{
	            	temp = inFile2.next();
	            }

Exception in thread "main" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Scanner.java:838)
at java.util.Scanner.next(Scanner.java:1347)
at ProcessScores.main(ProcessScores.java:35)