This Java tip illustrates an example of Quintessential Regular Expression search and replace program. This program finds all matches to a regular expression pattern and replaces them with another string.

 import java.util.regex.*;

public class BasicReplace {
    public static void main(String[] args) {
        CharSequence inputStr = "p q r p q r ";
        String patternStr = "q";
        String replacementStr = "s";
        // Compile regular expression
        Pattern pattern = Pattern.compile(patternStr);
        // Replace all occurrences of pattern in input
        Matcher matcher = pattern.matcher(inputStr);
        String output = matcher.replaceAll(replacementStr);
        // p s r p s r