如何删除字符串中$之后的空格？

Question

I have an input with a space between the $ and the value, and I'd like to remove the space. This code:

System.out.println("This costs $ 5 even.".replaceAll("\\$ ", "$"));

should print out:

This costs $5 even.

but it throws an exception:

Illegal group reference: group index is missing
java.lang.IllegalArgumentException
    at java.util.regex.Matcher.appendReplacement(Matcher.java:819)
    at java.util.regex.Matcher.replaceAll(Matcher.java:955)
    at java.lang.String.replaceAll(String.java:2223)
    at DollarTest.test(DollarTest.java:18)

What am I missing?

Answer 1

只需使用replace() ：

System.out.println("This costs $ 5 even.".replace("$ ", "$"));

Answer 2

The problem is that in a regex replacement string, the $ is special. It is supposed to be used to refer to a capturing group of the regex itself.

You need to escape it:

.replaceAll("\\$ ", "\\$")

But as @pp_ mentions , you are better off using a plain .replace() here.

Answer 3

Another alternative - group the $ and the value, around the space, then concat them in the replacement.

String s = "This costs $ 5 even. That costs $ 6 even. This is a $ sign.";
System.out.println(s.replaceAll("(\\$)\\s(\\d+)", "$1$2"));

Output

This costs $5 even. That costs $6 even. This is a $ sign.

It also points out a flaw in the other answers

String s = "This costs $ 5 even. That costs $ 6 even. This is a $ sign.";
System.out.println(s.replaceAll("\\$ ", "\\$"));

Outputs "$sign" .

This costs $5 even. That costs $6 even. This is a $sign.

Answer 4

I'd suggest you to use following regex to remove any number of spaces between $ and next number.

try {
    String data = "This costs $          7 even";
    String resultString = data.replaceAll("(?is)(?<=\\$)\\s*(?=\\d+)", "");
    System.out.println(resultString);

} catch (PatternSyntaxException ex) {

}

Input:

This costs $ 5 even
This costs $6 even
This costs $          7 even
This costs $          77 even
This costs $          7.2 even
This costs $          0.21 even
It's cost is between $   5.2 and $   8.3
You don't have to pay top $ for this.

Output:

This costs $5 even
This costs $6 even
This costs $7 even
This costs $77 even
This costs $7.2 even
This costs $0.21 even
It's cost is between $5.2 and $8.3
You don't have to pay top $ for this.