Things we might want to do Finding patterns using regular expressions Manipulating Strings Splitting Processing Tokens

Basic methods to review Substring(), charAt(), indexOf(),

toLowerCase(), startsWith(), endsWith(), firstIndexOf(), lastIndexOf(), trim(), length()

Regular expressions is a syntax for pattern matching used by many programming languages

Examples of regular expression syntax: [aceF] matches any of the letters enclosed in [ ] * matches zero or more occurrences of a pattern + matches one or more occurrences of a pattern \s matches whitespace

String methods that use regular expressions include matches(), split(), replaceAll()

More concrete examples are on the following slides

Note: This page is a brief overview; regular expression syntax has much more in it

Problem: A String is an immutable object Bad solution (1453 milliseconds on my computer):

Repeatedly create a new string from an old one String str; for (int i=0; i<10000; i++) str += “abcdef”;

Better solution (0 milliseconds on my computer): Use StringBuilder, a mutable string class

StringBuilder build = new StringBuilder(10000);For (int i=0; i<10000; i++) { build.append(“abcdef”); }String str = build.toString();

Extracting information from a string Example:

String date = "January 23, 1923 10:32:15 pm"; String[] data = date.split("[, :]+"); for (int i=0; i<data.length; i++) System.out.println(data[i]);

The argument to split: determines how the date is converted to an array Characters enclosed between [ and ] are delimiters

Space, comma and colon Split when one or more (+) delimiters are found in

a row

OutputJanuary231923103215pm

Definition: A token is a group of characters treated as a unit

String Tokenizer classString expression = "((3.5 + 52)/234 + 75.2*83.9 - 9.0";// The next line removes white spaceexpression = expression.replaceAll("\\s+",""); StringTokenizer tokenizer = new StringTokenizer(expression, "()+-/*", true);

while (tokenizer.hasMoreTokens()){ System.out.println(tokenizer.nextToken()); }

Output((3.5 +52)/234 +75.2*83.9 -9.0

Definition: white space includes space, tab, new line characters