How to replace a special character with single slash
java
Solution
On escape sequences
A declaration like:
String s = "\\";
defines a string containing a single backslash. That is, `s.length() == 1`.
This is because `\` is a Java escape character for `String` and `char` literals. Here are some other examples:
- `"\n"` is a `String` of length 1 containing the newline character
- `"\t"` is a `String` of length 1 containing the tab character
- `"\""` is a `String` of length 1 containing the double quote character
- `"\/"` contains an invalid escape sequence, and therefore is not a valid `String` literal
- it causes compilation error
Naturally you can combine escape sequences with normal unescaped characters in a `String` literal:
System.out.println("\"Hey\\\nHow\tare you?");
The above prints (tab spacing may vary):
"Hey\
How are you?
References
- JLS 3.10.6 Escape Sequences for Character and String Literals
See also
- Is the char literal `'\"'` the same as `'"'` ?(backslash-doublequote vs only-doublequote)
Back to the problem
Your problem definition is very vague, but the following snippet works as it should:
System.out.println("How are you? Really??? Awesome!".replace("?", "\\?"));
The above snippet replaces `?` with `\?`, and thus prints:
How are you\? Really\?\?\? Awesome!
If instead you want to replace a `char` with another `char`, then there's also an overload for that:
System.out.println("How are you? Really??? Awesome!".replace('?', '\\'));
The above snippet replaces `?` with `\`, and thus prints:
How are you\ Really\\\ Awesome!
`String` API links
- `replace(CharSequence target, CharSequence replacement)`
- Replaces each substring of this string that matches the literal `target` sequence with the specified literal `replacement` sequence.
- `replace(char oldChar, char newChar)`
- Returns a new string resulting from replacing all occurrences of `oldChar` in this string with `newChar`.
On how regex complicates things
If you're using `replaceAll` or any other regex-based methods, then things becomes somewhat more complicated. It can be greatly simplified if you understand some basic rules.
- Regex patterns in Java is given as `String` values
- Metacharacters (such as `?` and `.`) have special meanings, and may need to be escaped by preceding with a backslash to be matched literally
- The backslash is also a special character in replacement `String` values
The above factors can lead to the need for numerous backslashes in patterns and replacement strings in a Java source code.
It doesn't look like you need regex for this problem, but here's a simple example to show what it can do:
System.out.println(
"Who you gonna call? GHOSTBUSTERS!!!"
.replaceAll("[?!]+", "<$0>")
);
The above prints:
Who you gonna call<?> GHOSTBUSTERS<!!!>
The pattern `[?!]+` matches one-or-more (`+`) of any characters in the character class `[...]` definition (which contains a `?` and `!` in this case). The replacement string `<$0>` essentially puts the entire match `$0` within angled brackets.
Related questions
- Having trouble with Splitting text. - discusses common mistakes like `split(".")` and `split("|")`
Regular expressions references
- regular-expressions.info
- Character class and Repetition with Star and Plus
- `java.util.regex.Pattern` and `Matcher`
Problem
I have a question about strings in Java. Let's say, I have a string like so: ``` String str = "The . startup trace ?state is info?"; ``` As the string contains the special character like `"?"` I need the string to be replaced with `"\?"` as per my requirement. How do I replace special characters with `"\"`? I tried the following way. ``` str.replace("?","\?"); ``` But it gives a compilation error. Then I tried the following: ``` str.replace("?","\\?"); ``` When I do this it replaces the special characters with `"\\"`. But when I print the string, it prints with single slash. I thought it is taking single slash only but when I debugged I found that the variable is taking `"\\"`. Can anyone suggest how to replace the special characters with single slash (`"\"`)?