String Methods

The String class provides methods that use regular expressions.

matches(regex) returns true if the string matches the pattern.

The pattern must match the entire string, not just part of it.

"Hello, World".matches("\\w+");       // false
"Hello, World".matches("\\w*, \\w+"); // true

split(regex) returns a String array containing substrings from the original that were separated by text matching the regex.

The matched delimiter text is discarded.

String data = "One potato,two potahto,  three potayto, four";
String[] fields = data.split(",\\s*");
for (String field : fields) {
  System.out.println("Field: " + field);
}

replaceFirst(regex, replacement) returns a string with the first match of the regex replaced by the replacement string.

The original string remains unchanged (a String is immutable after all).

String data = "One potato,two potahto,  three potayto, four";
System.out.println(data.replaceFirst("po\\w+to", "giraffe"));
// One giraffe,two potahto,  three potayto, four
System.out.println(data);
// One potato,two potahto,  three potayto, four

replaceAll() replaces all matches with the replacement.

String data = "One potato,two potahto,  three potayto, four";
System.out.println(data.replaceAll("po\\w+to", "giraffe"));
// One giraffe,two giraffe,  three giraffe, four

Drill¶

RegularExpressionsJava/src/com.example.java2.drills.Splitter * The file pets.txt has records whose fields are separated by a tab that's optionally preceded by a comma. * Add code to the loop to use a regex with split to split each line and use the fields to construct a Pet object and add it to the list.

Practice Exercise¶

These methods do not take parameters for setting regex options like CASE_INSENSITIVE and MULTILINE. However, you can use embedded flags in your regex string itself:
String regex = "(?i)(?m)^error"; // set CASE_INSENSITIVE and MULTILINE

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