Why am I getting a StringIndexOutOfBoundsException when I try to replace `\\` with `\`?

Question

I have to replace \\ with \ in Java. The code I am using is

System.out.println( (MyConstants.LOCATION_PATH + File.separator + myObject.getStLocation() ).replaceAll("\\\\", "\\") );

But I don't know why it is throwing StringIndexOutOfBoundsException.

It says String index out of range: 1

What could be the reason? I guess it is because the first argument replaceAll accepts a pattern. What could be the possible solution?

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Stacktrace

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 1
    at java.lang.String.charAt(String.java:558)
    at java.util.regex.Matcher.appendReplacement(Matcher.java:696)
    at java.util.regex.Matcher.replaceAll(Matcher.java:806)
    at java.lang.String.replaceAll(String.java:2000)

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Answer Found

asalamon74 posted the code I required, but I don't know why he deleted it. In any case here it is.

There is a bug already filed in Java's bug database. (Thanks for this reference, asalamon.)

yourString.replaceAll("\\\\", "\\\\");

Amazingly, both search and replace string are the same :) but still it does what I require.

Answer 1

Use String.replace instead of replaceAll to avoid it using a regex:

String original = MyConstants.LOCATION_PATH + File.seperator 
    + myObject.getStLocation();
System.out.println(original.replace("\\\\", "\\"));

Personally I wouldn't do it this way though - I'd create MyConstants.LOCATION_PATH_FILE as a File and then you could write:

File location = new File(MyConstants.LOCATION_PATH_FILE,
                         myObject.getStLocation());

which will do the right thing automatically.

Answer 2

Well, i tried

    String test = "just a \\ test with some \\\\ and others \\\\ or \\ so";
    String result = test.replaceAll("\\\\", "\\\\");
    System.out.println(test);
    System.out.println(result);
    System.out.println(test.equals(result));

and got, as expected

just a \ test with some \\ and others \\ or \ so
just a \ test with some \\ and others \\ or \ so
true

What you really need is

string.replaceAll("\\\\\\\\", "\\\\");

to get

just a \ test with some \\ and others \\ or \ so
just a \ test with some \ and others \ or \ so
false

You want to find: \\  (2 slashes)
which needs to be escaped in the regex: \\\\ (4 slashes)
and escaped in Java: "\\\\\\\\" (8 slashes)
same for the replacement...

Answer 3

For the regex, if you want to change \ to \\, you should do this:

if (str.indexOf('\\') > -1)
    str = str.replaceAll("\\\\", "\\\\\\\\");
str = "\"" + str + "\"";

Where \\\\ means \ and \\\\\\\\ means \\.

Answer 4

File.seperator is already escaped as is any string object so you are escaping them twice.

You only need to escape values that you are entering as a string literal.

Answer 5

The best way is :

str.replace(**'**\\**'**, **'**/**'**); //with char method not String

Answer 6

Try this

cadena.replaceAll("\\\\","\\\\\\\\")