Problem with CHAR

Hello, all!

Working on a program to take a string, iterate through each character on at a time, modify those characters by an offset value to change them into new characters, and spit out the result. Having an odd issue trying to assign a character from a StringBuffer to a char.

Code:

---

for (int i = 0; i <= text.length(); i--)
                {
                        // Pull one character from string
                        char tempChar = text.charAt(i);
                        // Get the value of the character
                        value = Character.getNumericValue(tempChar);
                        if (negative = true)
                                // Adjust the value of the character by the offset
                                value = value - offset;
                        else
                                // Adjust the value of the character by the offset
                                value = value + offset;
                        // Convert value back into a character
                        tempChar = (char) value;
                        // Append to result string
                        result.append(Character.toString(tempChar));
                }

---

Line 4 of that bit is where I'm getting an index out of range: -1 exception. text is a StringBuffer.

Any ideas? Clearly I've done something wrong.

Thanks in advance!

Why are you looping down: i-- and not up i++? Am I missing something?

No. You're not. But apparently I am. That's what I was missing.

I was originally counting down. Epic fail!

Thanks so much. :P

You're welcome!

"i <= text.length()"

If you are indexing you may not go up to equal the length because you start with element zero -> you will be out of range probably here too.

Whenever you use a for loop to iterate through any array, the normal convention is to start with

Code:

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i=0

---

and you always test for

Code:

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i<array.length

---

. You won't see most java programmers testing for

Code:

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i<=array.length-1

---

So the conventional for loop will look like this and ensure you don't generate an ArrayIndexOutOfBoundsException.

Code:

---

int[]  ints = {1,3,5,7,9,11};
int[]  newints = new int[ints.length];  // Have to initialize the new array.  Make it the same size as the source for my copy

for (int i=0; i<ints.length; i++)  {  // Arrays such as this use ".length" for their size. 
                                      // Other things will have .length() or .size() methods.
        newints[i] = ints[i];
}

---

Right. I understand how a for statement iterates through something. Or at least I think I do... Yet I'm getting a StringIndexOutofBounds Exception equal to the length of the string I'm trying to process. Not sure why, exactly. I'm using a StringBuffer, but the .length() method should still function the same.

Code:

---

        public String encrypt(int offset)
        {
                int value;
               
                // Iterate from = to the length of the string
                for (int i = 0; i <= text.length(); i++)
                {
                        // Pull one character from string
                        char tempChar = text.charAt(i);
                        // Get the value of the character
                        value = Character.getNumericValue(tempChar);
                        if (negative = true)
                                // Adjust the value of the character by the offset
                                value = value - offset;
                        else
                                // Adjust the value of the character by the offset
                                value = value + offset;
                        // Convert value back into a character
                        tempChar = (char) value;
                        // Append to result string
                        result.append(Character.toString(tempChar));
                }
               
                return text.toString();
        }

---

Any ideas?

Your problem is in your for statement's comparator. All arrays, including strings, in Java have zero origin. That means you go from i=0 to i<thing.length(). Not i<=thing.length(). Your out of bounds exception is due to this.

Ahh. That makes perfect sense. Brilliant.

Thanks!

Aaaaand, unfortunately now I have another problem. The loop iterates correctly, but returns blank characters. Perhaps char int values don't work the way I think they do?

I'd thought that, for example, the unicode value of 'A' would return 65. Adjusting this by 3 would then return 'D'. But clearly that isn't the case.

Perhaps someone could explain? :]

Generally, that cast of the int as char should be fine. But I do see a problem here on this if statement from your earlier post:

Code:

---

if (negative = true)

---

Did you really intend to assign the value of true to the variable negative? Or were you testing if the value of negative had been set to true?

I was testing if the value of negative had been set to true, but I simplified it to just test the condition that negative represents. Here's the updated version.

Code:

---

        public StringBuffer encrypt(int offset)
        {
                int value;
               
               
               
                // Iterate from = to the length of the string
                for (int i = 0; i < text.length(); i++)
                {
                        // Pull one character from string
                        char tempChar = text.charAt(i);
                        // Get the value of the character
                        value = Character.getNumericValue(tempChar);
                        if (offset < 0)
                                // Adjust the value of the character by the offset
                                value = value - offset;
                        else
                                // Adjust the value of the character by the offset
                                value = value + offset;
                        // Convert value back into a character
                        tempChar = (char) value;
                        // Append to result string
                        result.append((tempChar));
                }
               
                return result;
        }

---

I don't think you are doing what you really want to then. If the offset is negative, what happens when you subtract it from a value. Two negatives make a..... ;-)

You do not need to check the offset at all. It's an offset, I would simply add it and be done. If it's negative, you're adding a negative (i.e. subtracting the absolute value). If it's positive you're adding it. Done.

Quote:

---

Originally Posted by jlczuk

I don't think you are doing what you really want to then. If the offset is negative, what happens when you subtract it from a value. Two negatives make a..... ;-)

You do not need to check the offset at all. It's an offset, I would simply add it and be done. If it's negative, you're adding a negative (i.e. subtracting the absolute value). If it's positive you're adding it. Done.

---

Yeah, I realized the math on that was bad after I posted it. But that's not the main problem. The problem is that when a take a char and create a new char using the int value of the original char modified by an offset number or some sort I get nothing but blank space. Even with bad math, I would still get some sort of char.

Thanks for catching that though. :]

Ok, I see the real problem now. What is the string you are constructing and what is the one you are returning?

Sorry for spamming my posts, I'm getting tired and trying to do too much too quickly.

One other thing I noticed. I don't see where either the result or text variables are being initialized prior to entering that method. Generally speaking, it isn't a good idea to modify instance variables from inside a method like that as a side-effect. If that is the method's clear intention, that is fine. But the method is returning a string, that happens to be an instance variable (which is a bit redundant) and also updating the result instance variable.

I think that result should be local to that method. If you want to set an instance variable to what that method returns, that's fine.

Uh. I'm assigning user input to a stringbuffer called text, iterating each character in that stringbuffer through my for loop to alter the characters, and appending them to an empty results stringbuffer that is outputted to the display. The return string is always the result of the original "text" string being run through that loop.

Can you please post a fresh copy of the code? I'm having trouble finding the right one to look at.

Yeah, the use of class variables is intended there. In case I'd like to re-use either the original string or the modified result later.

Code:

---

public StringBuffer encrypt(int offset)
        {
                int value;
                System.out.println(text);
               
               
                // Iterate from = to the length of the string
                for (int i = 0; i < text.length(); i++)
                {
                        // Pull one character from string
                        char tempChar = text.charAt(i);
                        // Get the value of the character
                        value = Character.getNumericValue(tempChar);
                        if (offset < 0)
                                // Adjust the value of the character by the offset
                                value -= Math.abs(offset);
                        else
                                // Adjust the value of the character by the offset
                                value += offset;
                        // Convert value back into a character
                        tempChar = (char) value;
                        // Append to result string
                        result.append((tempChar));
                }
               
                return result;
        }

---

And those variables are declared as

Code:

---

        private StringBuffer text = new StringBuffer("");
        private StringBuffer result = new StringBuffer("");

---