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Thread: Little String Problem

  1. #1
    Member tyeeeee1's Avatar
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    Default Little String Problem

    Hey, I've just started messing around with reading from text documents and I've done fairly well in my experiments so-far; I just ran into a small problem with the one part of the code that I was sure would work. When running the program everything runs perfectly except for my if statements. Every single character, which is either a 1 or a 0, is always printing ""+charText+" is null." when I run the program. I haven't done much with strings/char variables before so I'm probably making some simple mistake, if anyone can enlighten me please do so.

    MapReaderTest.java
    import java.io.*;
     
    class MapReaderTest
    {
    	public static void main (String args[]) throws IOException
    	{
    		String lineText;
    		char charText;
    		int lineCounter =0;
    		int characterCounter = 0;
     
    		BufferedReader inputStream = new BufferedReader(new FileReader("Map.txt"));
     
    		while( (lineText = inputStream.readLine()) != null) //While the current line doesn't have nothingon it then keep looping
    		{
    			lineCounter++;
    			System.out.println(""+lineText+" is the current line.");
     
    			for(int i = 0; i < lineText.length(); i++) //Loops through each character in the string until the string ends.
    			{
    				charText = lineText.charAt(i);
     
    				if(charText == 0)
    				{
    					System.out.println(""+charText+" is a zero.");
    				}
    				else if(charText == 1)
    				{
    					System.out.println(""+charText+" is a one.");
    				}
    				else
    				{
    					System.out.println(""+charText+" is null.");
    				}
    			}
    		}
    		inputStream.close();
    	}
    }

    Map.txt
    0110101101
    1001010010
    0001110001
    1110001100


  2. #2
    Super Moderator pbrockway2's Avatar
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    Default Re: Little String Problem

    charText is a variable of type char, so it won't ever be null - rather it should have some numeric value.

    The output from
    System.out.println(""+charText+" is null.");

    should have told you what that value is for the two characters. If the char values of the zero and one characters are not clear to you from the program's output, post that output.

    The two char values you test for (0 an 1) are very likely not the values associated with the zero an one characters. Rather than try and commit to memory all the values we use character literal notation:

    if(charText == '0') // '0' is a character literal
    {
        // this code will be executed when charText is the zero character.
    }

  3. The Following User Says Thank You to pbrockway2 For This Useful Post:

    tyeeeee1 (January 9th, 2013)

  4. #3
    Super Moderator Norm's Avatar
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    Default Re: Little String Problem

    To see the difference between: 0 and '0' use a cast on the char value when you print it:
     System.out.println("'0'="+(int)'0');
    Also look at a table of ASCII character values.

    As pbrockway2 said, you should always code char literals: '0' vs their int value: 48
    If you don't understand my answer, don't ignore it, ask a question.

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