Java 正则表达式 (?i) 与 Pattern.CASE_INSENSITIVE
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Java regex (?i) vs Pattern.CASE_INSENSITIVE
提问by Paddy
I'm using "\\b(\\w+)(\\W+\\1\\b)+"along with input = input.replaceAll(regex, "$1");to find duplicate words in a string and remove the duplicates. For example the string input = "for for for" would become "for".
我正在使用"\\b(\\w+)(\\W+\\1\\b)+"withinput = input.replaceAll(regex, "$1");在字符串中查找重复的单词并删除重复项。例如，字符串 input = "for for for" 将变为 "for"。
However it is failing to turn "Hello hello" into "Hello" even though I have used Pattern p = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
然而，即使我使用过它也无法将“Hello hello”变成“Hello” Pattern p = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
I can correct it by using "(?i)\\b(\\w+)(\\W+\\1\\b)+"but I want to know why this is necessary? Why do I have to use the (?i) flag when I have already specified Pattern.CASE_INSENSITIVE?
我可以通过使用来纠正它，"(?i)\\b(\\w+)(\\W+\\1\\b)+"但我想知道为什么这是必要的？当我已经指定了 Pattern.CASE_INSENSITIVE 时，为什么我必须使用 (?i) 标志？
Heres the full code for clarity:
为了清楚起见，这里是完整的代码：
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class DuplicateWords {
public static void main(String[] args) {
String regex = "\b(\w+)(\W+\1\b)+";
Pattern p = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
Scanner in = new Scanner(System.in);
int numSentences = Integer.parseInt(in.nextLine());
while (numSentences-- > 0) {
String input = in.nextLine();
Matcher m = p.matcher(input);
// Check for subsequences of input that match the compiled pattern
while (m.find()) {
input = input.replaceAll(regex, "");
}
// Prints the modified sentence.
System.out.println(input);
}
in.close();
}
}
采纳答案by anubhava
Your problem is that you're defining a regex with CASE_SENSITIVEflag but not using it correctly in replaceAllmethod.
您的问题是您正在定义带有CASE_SENSITIVE标志的正则表达式，但没有在replaceAll方法中正确使用它。
You can also use (?i)in the middle of the regex for ignore case match of back-reference \1like this:
您还可以(?i)在正则表达式的中间使用忽略反向引用的大小写匹配，\1如下所示：
String repl = "Hello hello".replaceAll("\b(\w+)(\W+(?i:\1)\b)+", "");
//=> Hello
And then use Matcher.replaceAlllater.
然后Matcher.replaceAll稍后使用。
Working Code:
工作代码：
public class DuplicateWords {
public static void main(String[] args) {
String regex = "\b(\w+)(\W+(?i:\1)\b)+";
Pattern p = Pattern.compile(regex);
// OR this one also works
// String regex = "\b(\w+)(\W+\1\b)+";
// Pattern p = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
Scanner in = new Scanner(System.in);
int numSentences = Integer.parseInt(in.nextLine());
while (numSentences-- > 0) {
String input = in.nextLine();
Matcher m = p.matcher(input);
// Check for subsequences of input that match the compiled pattern
if (m.find()) {
input = m.replaceAll("");
}
// Prints the modified sentence.
System.out.println(input);
}
in.close();
}
}
