java regex replace pattern code example

Example 1: java string regexp replace

String input = "abcd";
Pattern p = Pattern.compile("regexp");
String output = p.matcher(input).replaceAll("replacement");

Example 2: replace regex group() java

Pattern p = Pattern.compile("(\\d)(.*)(\\d)");
String input = "6 example input 4";
Matcher m = p.matcher(input);
if (m.find()) {
    // replace first number with "number" and second number with the first
    String output = m.replaceFirst("number $3$1");  // number 46
}