Comparing \ in java

MRMadhav · 02-25-2006, 01:09 AM

Hi,
I have a function that compares the characters in a string 1 by 1. The problem is that I don't know how to compare the switch character "\". I tried using char but that also failed! Anyone knows how to do that?

paulsm4 · 02-25-2006, 01:21 AM

It's probably unwise to write your own character-by-character "strcmp()" in Java - my guess is that you'll probably be much better off using the built-in ".equals()" method, or ".equalsIgnoreCase()".

I'm not sure what you mean by "'\' switch character". If you mean "escape sequence" (as in "\n"), then it means exactly the same in Java as in C/C++ (except that it's a 16-bit Unicode character, e.g. '0x000a', instead of an 8-bit '0x0a'). If you mean "path separator", you can use the Java "File.separator" to determine if your platform uses a DOS "\" or a Linux "/".

MRMadhav · 02-25-2006, 02:31 AM

No what i mean that for eg in a JTextField the user types "12\4" instead of "12/4"
now I want to compare the string inputed 1 by 1 and replace any "\" by "/".
That is only an eg. the real thing is even more complex! My problem is that when you put "\" in java it takes \ as a switch character and the next character which is " is not taken as the closure of the string. thus I get Unclosed string literal error!

Flesym · 02-25-2006, 04:48 AM

Simply use "\\"

spooon · 02-25-2006, 04:49 AM

This doesn't make any sense. What you are talking about is escape sequences in string literals in the Java language. This is purely something that relates to how you write the source code, and has nothing to do with how the program actually works.

MRMadhav · 02-25-2006, 07:01 AM

Firstly you cannot compare 1 "\" with "\\" as this generates an error!!!
Then to answer to spooon my question is about how to write the source code itself as the behavior of the application is under control as long as the source code is correct!

jlliagre · 02-25-2006, 07:18 AM

Quote:

Originally Posted by MRMadhav

Firstly you cannot compare 1 "\" with "\\" as this generates an error!!!

You cannot write "\", it is a syntax error.

Quote:

Then to answer to spooon my question is about how to write the source code itself as the behavior of the application is under control as long as the source code is correct!

You have been answered to use "\\" to represent a string composed of the single backslash character.

MRMadhav · 02-25-2006, 07:40 AM

Code:

import java.io.*;

public class Test
{
	public static void main(String args[])
	{
		BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
		String text="";
		try{text = bf.readLine();}catch(IOException ex){System.out.println(ex);}
		boolean foundbackslash =false;
		for(int i=0;i<text.length();i++)
		{
			if(text.substring(i,i+1).matches("\\"))
			{
				foundbackslash=true;
			}
		}
		System.out.println(foundbackslash);
	}
}

when i use this i get this error:

Quote:

Exception in thread "main" java.util.regex.PatternSyntaxException: Unexpected internal error near index 1
\
^
at java.util.regex.Pattern.error(Pattern.java:1528)
at java.util.regex.Pattern.compile(Pattern.java:1286)
at java.util.regex.Pattern.<init>(Pattern.java:1035)
at java.util.regex.Pattern.compile(Pattern.java:779)
at java.util.regex.Pattern.matches(Pattern.java:865)
at java.lang.String.matches(String.java:1597)
at Test.main(Test.java:13)

Flesym · 02-25-2006, 10:56 AM

The method "matches" does not compare two Strings:
http://java.sun.com/j2se/1.5.0/docs/...a.lang.String)
But the method "equals" does, so:

Code:

if(text.substring(i, i+1).equals("\\")){
...
}

or even better:

Code:

if(text.charAt(i) == '\\'){
...
}

xhi · 02-25-2006, 09:51 PM

as has been said.. \ is not a character.. it is an escape.. so you have to escape the escape to test it.. so \\ in code is \ in plaintext..

\\ is \
\ does not exist..

clear as mud now im sure..

MRMadhav · 02-27-2006, 03:22 AM

Hey thanks for your anwers! So stupid of me not thinking about the equals method!
I tried it today and it works perfectly!! Thanks a lot guys!