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Exception Handling

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shaynicb25 shaynicb25 is offline

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Exception Handling

Aug 10th, 2008

I have to create a program that reads the text, outputs the text as is and prints the number of lines and the number of times each letter appears in the text. I have to include an exception, so that if the array index goes out of bounds when the program accesses the array letterCount, it throws and handles the ArrayIndexOutOfBoundsException. I have the program completed and working , but I'm having trouble adding the exception to the program. Here is my code:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
import java.io.*;
 
public class CharacterCount
{
    public static void main(String[] args)
                   throws FileNotFoundException, IOException
   {
          int lineCount = 0;
			 try
			 {
          int[] letterCount = new int[26];
			 }
			 catch (ArrayIndexOutOfBoundsException e)
			 {
			 System.err.println("Caught ArrayIndexOutOfBoundsException: "+ e.getMessage());
			 e.printStackTrace();
			 }
 
          IntClass next = new IntClass();
 
          FileReader inputStream = new FileReader("text.txt");
          PrintWriter outfile =
                  new PrintWriter(new FileWriter("textCh.out"));
 
          next.setNum(inputStream.read());
 
          while (next.getNum() != -1)
          {
              copyText(inputStream, outfile, next, letterCount);
              lineCount++;
              next.setNum(inputStream.read());
          }  //end while loop
 
          writeTotal(outfile, lineCount, letterCount);
 
          outfile.close();
    }
 
    static void copyText(FileReader infile, PrintWriter outfile,
                         IntClass next, int[] letterC) throws IOException
    {
          while (next.getNum() != (int)'\n')
          {
              outfile.print((char)(next.getNum()));
              chCount((char)(next.getNum()), letterC);
              next.setNum(infile.read());
          }
          outfile.println();
    }
 
    static void chCount(char ch, int[] letterC)
    {
          int index;
          int i;
 
          ch = Character.toUpperCase(ch);   //Step a
          index = (int) ch - 65;            //Step b
          if (index >= 0 && index < 26)      //Step c
            letterC[index]++;
    }
 
    static void writeTotal(PrintWriter outfile, int lines,
                           int[] letters)
    {
          int i;
 
          outfile.println();
          outfile.println("The number of lines = " + lines);
 
          for (i = 0; i < 26; i++)
              outfile.println((char)(i + 65) + " count = "
                             + letters[i]);
    }
}
import java.io.*;

public class CharacterCount
{
    public static void main(String[] args)
                   throws FileNotFoundException, IOException
   {
          int lineCount = 0;
			 try
			 {
          int[] letterCount = new int[26];
			 }
			 catch (ArrayIndexOutOfBoundsException e)
			 {
			 System.err.println("Caught ArrayIndexOutOfBoundsException: "+ e.getMessage());
			 e.printStackTrace();
			 }

          IntClass next = new IntClass();

          FileReader inputStream = new FileReader("text.txt");
          PrintWriter outfile =
                  new PrintWriter(new FileWriter("textCh.out"));

          next.setNum(inputStream.read());

          while (next.getNum() != -1)
          {
              copyText(inputStream, outfile, next, letterCount);
              lineCount++;
              next.setNum(inputStream.read());
          }  //end while loop

          writeTotal(outfile, lineCount, letterCount);

          outfile.close();
    }
	 	 
    static void copyText(FileReader infile, PrintWriter outfile,
                         IntClass next, int[] letterC) throws IOException
    {
          while (next.getNum() != (int)'\n')
          {
              outfile.print((char)(next.getNum()));
              chCount((char)(next.getNum()), letterC);
              next.setNum(infile.read());
          }
          outfile.println();
    }

    static void chCount(char ch, int[] letterC)
    {
          int index;
          int i;

          ch = Character.toUpperCase(ch);   //Step a
          index = (int) ch - 65;            //Step b
          if (index >= 0 && index < 26)      //Step c
            letterC[index]++;
    }

    static void writeTotal(PrintWriter outfile, int lines,
                           int[] letters)
    {
          int i;

          outfile.println();
          outfile.println("The number of lines = " + lines);

          for (i = 0; i < 26; i++)
              outfile.println((char)(i + 65) + " count = "
                             + letters[i]);
    }
}

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lich

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Re: Exception Handling

Aug 11th, 2008

try
{
<you code here>
}

catch (ArrayIndexOutOfBounds evt)
{
System.out.println(" Ur Message");
}

catch(NumberFormatException evt2)
{

System.out.println("Ur Message");
}

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Re: Exception Handling

Aug 11th, 2008

First of all, this:
int[] letterCount = new int[26] ;
does not throw an exception.
Second: Let me guess your program does not compile. This is why:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
try
			 {
          int[] letterCount = new int[26];
			 }
			 catch (ArrayIndexOutOfBoundsException e)
			 {
			 System.err.println("Caught ArrayIndexOutOfBoundsException: "+ e.getMessage());
			 e.printStackTrace();
			 }
try
			 {
          int[] letterCount = new int[26];
			 }
			 catch (ArrayIndexOutOfBoundsException e)
			 {
			 System.err.println("Caught ArrayIndexOutOfBoundsException: "+ e.getMessage());
			 e.printStackTrace();
			 }

You declare letterCount inside the try { ... }. Meaning that outside try{...} no one can "see" it. So when you try to use it at the while loop you will get an error. If you have to give value to a variable inside the try{...} but you will have to use it outside as well then:

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int[] letterCount = null;
try
			 {
          letterCount = new int[26];
			 }
			 catch (ArrayIndexOutOfBoundsException e)
			 {
			 System.err.println("Caught ArrayIndexOutOfBoundsException: "+ e.getMessage());
			 e.printStackTrace();
			 }
int[] letterCount = null;
try
			 {
          letterCount = new int[26];
			 }
			 catch (ArrayIndexOutOfBoundsException e)
			 {
			 System.err.println("Caught ArrayIndexOutOfBoundsException: "+ e.getMessage());
			 e.printStackTrace();
			 }

You declare letterCount outside try{} so anyone can see it.
By the way the above is not necessary, since the declaration does not throw an ArrayIndexOutOfBoundsException, unless you use negative value. And it is not very correct to catch such exceptions. It is up to the programmer to check in the code and make sure that you will never try to access an element of an array with an index greater than the length.

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
//try {
          int[] letterCount = new int[26];
/*
			 } catch (ArrayIndexOutOfBoundsException e) {
			 System.err.println("Caught ArrayIndexOutOfBoundsException: "+ e.getMessage());
			 e.printStackTrace();
			 }
*/
//try {
          int[] letterCount = new int[26];
/*
			 } catch (ArrayIndexOutOfBoundsException e) {
			 System.err.println("Caught ArrayIndexOutOfBoundsException: "+ e.getMessage());
			 e.printStackTrace();
			 }
*/

Try it without the try-catch.

As for you question, remove the throws Exception, from the main. You use these at method declarations in order to be caught by the method that calls the first method. No one calls main. Example:

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 Java Syntax (Toggle Plain Text) 
void A() throws Exception {
}
 
void B() {
  try {
    A();
  } catch (Exception e) {
  }
}
void A() throws Exception {
}

void B() {
  try {
    A();
  } catch (Exception e) {
  }
}

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Join Date: Jun 2008

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Re: Exception Handling

Aug 11th, 2008

Yes, including a throws on the end of main is considered bad programming practice since nothing can really catch an error generated from main and handle it afterward.

Only use throws on the end of main to save time when practicing something particular without bloating the code in try-catch blocks.

Use File I/O or Networking extensively for an example.

Last edited by Alex Edwards; Aug 11th, 2008 at 4:20 am.

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Re: Exception Handling

Aug 11th, 2008

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
IntClass next = new IntClass();
 
          FileReader inputStream = new FileReader("text.txt");
          PrintWriter outfile =
                  new PrintWriter(new FileWriter("textCh.out"));
 
          next.setNum(inputStream.read());
 
          while (next.getNum() != -1)
          {
              copyText(inputStream, outfile, next, letterCount);
              lineCount++;
              next.setNum(inputStream.read());
          }  //end while loop
 
          writeTotal(outfile, lineCount, letterCount);
 
          outfile.close();
IntClass next = new IntClass();

          FileReader inputStream = new FileReader("text.txt");
          PrintWriter outfile =
                  new PrintWriter(new FileWriter("textCh.out"));

          next.setNum(inputStream.read());

          while (next.getNum() != -1)
          {
              copyText(inputStream, outfile, next, letterCount);
              lineCount++;
              next.setNum(inputStream.read());
          }  //end while loop

          writeTotal(outfile, lineCount, letterCount);

          outfile.close();

The above code needs to be altered like this:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
IntClass next = new IntClass();
FileReader inputStream = null;
PrintWriter outfile = null;
 
try {
           inputStream = new FileReader("text.txt");
           outfile = new PrintWriter(new FileWriter("textCh.out"));
 
          next.setNum(inputStream.read());
 
          while (next.getNum() != -1)
          {
              copyText(inputStream, outfile, next, letterCount);
              lineCount++;
              next.setNum(inputStream.read());
          }  //end while loop
 
          writeTotal(outfile, lineCount, letterCount);
 
          outfile.close();
} catch (Exception e) {
System.out.println(e.getMessage());
}
IntClass next = new IntClass();
FileReader inputStream = null;
PrintWriter outfile = null;

try {
           inputStream = new FileReader("text.txt");
           outfile = new PrintWriter(new FileWriter("textCh.out"));

          next.setNum(inputStream.read());

          while (next.getNum() != -1)
          {
              copyText(inputStream, outfile, next, letterCount);
              lineCount++;
              next.setNum(inputStream.read());
          }  //end while loop

          writeTotal(outfile, lineCount, letterCount);

          outfile.close();
} catch (Exception e) {
System.out.println(e.getMessage());
}

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Re: Exception Handling

Aug 11th, 2008

And something that I forgot:
NEVER, NEVER "hard code" the length of an array when you access it :

This:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 for (i = 0; i < 26; i++)
              outfile.println((char)(i + 65) + " count = "
                             + letters[i]);
 for (i = 0; i < 26; i++)
              outfile.println((char)(i + 65) + " count = "
                             + letters[i]);

Should become this:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 for (i = 0; i < letters.length ; i++)
              outfile.println((char)(i + 65) + " count = "
                             + letters[i]);
 for (i = 0; i < letters.length ; i++)
              outfile.println((char)(i + 65) + " count = "
                             + letters[i]);

And this:

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 Java Syntax (Toggle Plain Text) 
if (index >= 0 && index < 26)      //Step c
            letterC[index]++;
if (index >= 0 && index < 26)      //Step c
            letterC[index]++;

To this:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
if (index >= 0 && index < letters.length)      //Step c
            letterC[index]++;
if (index >= 0 && index < letters.length)      //Step c
            letterC[index]++;

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Re: Exception Handling

Aug 11th, 2008

•

Originally Posted by shaynicb25

I have to create a program that reads the text, outputs the text as is and prints the number of lines and the number of times each letter appears in the text. I have to include an exception, so that if the array index goes out of bounds when the program accesses the array letterCount, it throws and handles the ArrayIndexOutOfBoundsException. I have the program completed and working , but I'm having trouble adding the exception to the program. Here is my code:

Hi it's me again. Sorry for not checking what you wrote, I was only looking at the code you gave. It seems that I suggested not to use ArrayIndexOutOfBoundsException even though that is what you wanted.
Who told you to use this exception handling? Because what I suggested was generally correct: you don't want to catch such exception, but instead make sure it doesn't happen by checking the length of the array.
Anyway if you want ArrayIndexOutOfBoundsException here it is.:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
static void chCount(char ch, int[] letterC) throws ArrayIndexOutOfBoundsException {
          int index;
          int i;
 
          ch = Character.toUpperCase(ch);   //Step a
          index = (int) ch - 65;            //Step b
          if (index >= 0 && index < 26)      //Step c
            letterC[index]++;
    }
 
    static void writeTotal(PrintWriter outfile, int lines,
                           int[] letters)
    throws ArrayIndexOutOfBoundsException  {
          int i;
 
          outfile.println();
          outfile.println("The number of lines = " + lines);
 
          for (i = 0; i < 26; i++)
              outfile.println((char)(i + 65) + " count = "
                             + letters[i]);
    }
 
static void copyText(FileReader infile, PrintWriter outfile,
                         IntClass next, int[] letterC) throws IOException, ArrayIndexOutOfBoundsException 
    {
          while (next.getNum() != (int)'\n')
          {
              outfile.print((char)(next.getNum()));
              chCount((char)(next.getNum()), letterC);
              next.setNum(infile.read());
          }
          outfile.println();
    }
static void chCount(char ch, int[] letterC) throws ArrayIndexOutOfBoundsException {
          int index;
          int i;

          ch = Character.toUpperCase(ch);   //Step a
          index = (int) ch - 65;            //Step b
          if (index >= 0 && index < 26)      //Step c
            letterC[index]++;
    }

    static void writeTotal(PrintWriter outfile, int lines,
                           int[] letters)
    throws ArrayIndexOutOfBoundsException  {
          int i;

          outfile.println();
          outfile.println("The number of lines = " + lines);

          for (i = 0; i < 26; i++)
              outfile.println((char)(i + 65) + " count = "
                             + letters[i]);
    }

static void copyText(FileReader infile, PrintWriter outfile,
                         IntClass next, int[] letterC) throws IOException, ArrayIndexOutOfBoundsException 
    {
          while (next.getNum() != (int)'\n')
          {
              outfile.print((char)(next.getNum()));
              chCount((char)(next.getNum()), letterC);
              next.setNum(infile.read());
          }
          outfile.println();
    }

When you add throws to a method (methodA) declaration, if an exception of that kind occurs in the method then it will not give you trouble inside the method. You will not have to put try-catch inside the method. But instead you throw it to the method that called methodA.
The above method copyText has a throws because it calls chCount which throws an ArrayIndexOutOfBoundsException .

It depends where you want to handle it:

1st version:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
void A(String s) {
try {
  int i = Integer.parseInt(s);
  // do other stuff
  // perhaps return something if the method was not void
} catch(NumberFormatException nfe) {
  //handle it here
 //print a message
}
}
 
void B() {
  A("3");
  A("a");
}
void A(String s) {
try {
  int i = Integer.parseInt(s);
  // do other stuff
  // perhaps return something if the method was not void
} catch(NumberFormatException nfe) {
  //handle it here
 //print a message
}
}

void B() {
  A("3");
  A("a");
}

Or Version 2:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
void A(String s) throws NumberFormatException {
  int i = Integer.parseInt(s);
}
 
void B() {
try {
 A("3");
} catch (NumberFormatException nfe) {
  //handle it here
}
try {
 A("a");
} catch (NumberFormatException nfe) {
  //handle it here
}
 
 
}
void A(String s) throws NumberFormatException {
  int i = Integer.parseInt(s);
}

void B() {
try {
 A("3");
} catch (NumberFormatException nfe) {
  //handle it here
}
try {
 A("a");
} catch (NumberFormatException nfe) {
  //handle it here
}
  
  
}

So now that you have added the throws ArrayIndexOutOfBoundsException, go to where you call the methods and put them in a try-catch. Since in my suggestions I have already put your code in try-catch, simply add one more catch() { }

And please tell me who told you to use ArrayIndexOutOfBoundsException? And sorry for confusing you and for my many posts

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Re: Exception Handling

Aug 11th, 2008

This assignment was given to me by my professor. I have tried implementing the changes you wrote about but now I have 35 errors

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Re: Exception Handling

Aug 11th, 2008

post you final code

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Re: Exception Handling

#10

Aug 11th, 2008

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
import java.io.*;
 
public class CharacterCount
{
    public static void main(String[] args)
                   throws FileNotFoundException, IOException
   {
          int lineCount = 0;
          int[] letterCount = new int[26];
 
          IntClass next = new IntClass();
			 FileReader inputStream = null;
			 PrintWriter outfile = null;
 
			 try
			 {
 
          FileReader inputStream = new FileReader("text.txt");
          PrintWriter outfile =
                  new PrintWriter(new FileWriter("textCh.out"));
 
          next.setNum(inputStream.read());
 
          while (next.getNum() != -1)
          {
              copyText(inputStream, outfile, next, letterCount);
              lineCount++;
              next.setNum(inputStream.read());
          }  //end while loop
 
          writeTotal(outfile, lineCount, letterCount);
 
          outfile.close();
    }
	 catch (Exception e)
	 {
	 System.out.println(e.getMessage());
	 }
 
 
    static void copyText(FileReader infile, PrintWriter outfile,
                         IntClass next, int[] letterC) throws IOException, ArrayIndexOutOfBoundsException
    {
          while (next.getNum() != (int)'\n')
          {
              outfile.print((char)(next.getNum()));
              chCount((char)(next.getNum()), letterC);
              next.setNum(infile.read());
          }
          outfile.println();
    }
 
    static void chCount(char ch, int[] letterC)throws ArrayIndexOutOfBoundsException
 
    {
          int index;
          int i;
 
          ch = Character.toUpperCase(ch);   //Step a
          index = (int) ch - 65;            //Step b
          if (index >= 0 && index < 26)      //Step c
            letterC[index]++;
    }
 
    static void writeTotal(PrintWriter outfile, int lines,
                           int[] letters) throws ArrayIndexOutOfBoundsException
    {
          int i;
 
          outfile.println();
          outfile.println("The number of lines = " + lines);
 
          for (i = 0; i < 26; i++)
              outfile.println((char)(i + 65) + " count = "
                             + letters[i]);
    }
}
import java.io.*;

public class CharacterCount
{
    public static void main(String[] args)
                   throws FileNotFoundException, IOException
   {
          int lineCount = 0;
          int[] letterCount = new int[26];

          IntClass next = new IntClass();
			 FileReader inputStream = null;
			 PrintWriter outfile = null;
			 
			 try
			 {
			 
          FileReader inputStream = new FileReader("text.txt");
          PrintWriter outfile =
                  new PrintWriter(new FileWriter("textCh.out"));

          next.setNum(inputStream.read());

          while (next.getNum() != -1)
          {
              copyText(inputStream, outfile, next, letterCount);
              lineCount++;
              next.setNum(inputStream.read());
          }  //end while loop

          writeTotal(outfile, lineCount, letterCount);

          outfile.close();
    }
	 catch (Exception e)
	 {
	 System.out.println(e.getMessage());
	 }


    static void copyText(FileReader infile, PrintWriter outfile,
                         IntClass next, int[] letterC) throws IOException, ArrayIndexOutOfBoundsException
    {
          while (next.getNum() != (int)'\n')
          {
              outfile.print((char)(next.getNum()));
              chCount((char)(next.getNum()), letterC);
              next.setNum(infile.read());
          }
          outfile.println();
    }

    static void chCount(char ch, int[] letterC)throws ArrayIndexOutOfBoundsException
	 
    {
          int index;
          int i;

          ch = Character.toUpperCase(ch);   //Step a
          index = (int) ch - 65;            //Step b
          if (index >= 0 && index < 26)      //Step c
            letterC[index]++;
    }

    static void writeTotal(PrintWriter outfile, int lines,
                           int[] letters) throws ArrayIndexOutOfBoundsException
    {
          int i;

          outfile.println();
          outfile.println("The number of lines = " + lines);

          for (i = 0; i < 26; i++)
              outfile.println((char)(i + 65) + " count = "
                             + letters[i]);
    }
}