1. Advanced String handling
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()

2. Pattern matching
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

3. Manipulationg Strings
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();

4. Splitting tokens Extracting information from a string
Output
January pm
Splitting tokens
Extracting information from a string
Example: String date = "January 23, :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
Definition: A token is a group of characters treated as a unit

5. Another way to split tokens
Output
( ( ) / *
Another way to split tokens
String Tokenizer class
String expression
= "(( )/ * ";
// The next line removes white space
expression = expression.replaceAll("\\s+","");
StringTokenizer tokenizer
= new StringTokenizer(expression, "()+-/*", true);
while (tokenizer.hasMoreTokens()) { System.out.println(tokenizer.nextToken()); }
Definition: white space includes space, tab, new line characters