Case-insensitive replaceAll in Java

September 10, 2009Tagged: javaregex

The replaceAll function in the java.lang.String class replaces each substring found in that matches the regular expression to replace.

String sentence = "The sly brown fox jumped over the lazy fox.";
String result = sentence.replaceAll("fox", "doggie");
System.out.println("Input: " + sentence);
System.out.println("Output: " + result);

Would output:

Input: The sly brown fox jumped over the lazy fox. Output: The sly brown doggie jumped over the lazy doggie.

However there are cases where we want to replaceall substrings and ignore the case, or make it case insensitive.

String sentence = "The sly brown Fox jumped over the lazy foX.";
String result = sentence.replaceAll("fox", "dog");
System.out.println("Input: " + sentence);
System.out.println("Output: " + result);

Input: The sly brown Fox jumped over the lazy foX. Output: The sly brown Fox jumped over the lazy foX.

To create the case sensitive version of replaceAll we do not need to create a new wrapper function or create a utility class somewhere. All we need to do is prepend the Case-insensitve pattern modifier (?i) before our regex to indicate that we don’t care about the case sensitivity of the regex.

String sentence = "The sly brown Fox jumped over the lazy foX.";
String result = sentence.replaceAll("(?i)fox", "dog");
System.out.println("Input: " + sentence);
System.out.println("Output: " + result);

Input: The sly brown Fox jumped over the lazy foX. Output: The sly brown dog jumped over the lazy dog.


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Written by Jelani Harris who lives and works in Wisconsin building useful things. You should follow them on Twitter