如何替换仅出现一次的子字符串，而连续两次或多次排除子字符串呢？

Question

Is there any way that I can do the following in java ?

String s = "acdaaefacaa";
String b = s.replaceLikeMethod("a", "");

and b becomes "cdaaefcaa". Basically replace any occurrence of the first string "a" with the other one "" unless "a" appears two or more times in a row.

Answer 1

You can use regex to achieve this. The features you want are

1. Negative LookBehind (?<!foo) Match pattern unless foo occurs right before.
2. Negative LookAhead. (?!foo) Match pattern unless foo occurs right afterwards

You basically need to use both at the same time with the same string as the string to match and pattern. Eg

String pattern = "(?<!foo)foo(?!foo)";

Or to easily replace with a string known at runtime like "a"

String pattern = "(?<!foo)foo(?!foo)".replace("foo", "a");

Finally, to replace just do :

String b = s.replaceAll(pattern, "");

Answer 2

Use this regex: ((?<!a)a(?!a)) . It uses negative lookahead and lookbehind. It matches every a that is not preceded and followed by another a .

Test:

String input = "acdaaefacaa";
String output = input.replaceAll("((?<!a)a(?!a))", "");
System.out.println(output);

Outputs:

cdaaefcaa