When we have a situation where strings contain multiple pieces of information (for example, when reading in data from a file on a line-by-line basis), then we will need to parse (i.e., divide up) the string to extract the individual pieces.
Issues to consider when parsing a string:
We want to divide up a phrase into words where spaces are used to separate words. For example
the music made it hard to concentrate
String phrase = "the music made it hard to concentrate"; String delims = "[ ]+"; String tokens = phrase.split(delims);
for (int i = 0; i < tokens.length; i++) System.out.println(tokens[i]);
Suppose each string contains an employee's last name, first name, employee ID#, and the number of hours worked for each day of the week, separated by commas. So
String employee = "Smith,Katie,3014,,8.25,6.5,,,10.75,8.5"; String delims = "[,]"; String tokens = employee.split(delims);
After this code executes, the tokens array will contain ten strings (note the empty strings): "Smith", "Katie", "3014", "", "8.25", "6.5", "", "", "10.75", "8.5"
There is one small wrinkle to be aware of (regardless of how consecutive delimiters are handled): if the string starts with one (or more) delimiters, then the first token will be the empty string ("").
Suppose we have a string containing several English sentences that uses only commas, periods, question marks, and exclamation points as punctuation. We wish to extract the individual words in the string (excluding the punctuation). In this situation we have several delimiters (the punctuation marks as well as spaces) and we want to treat consecutive delimiters as one
String str = "This is a sentence. This is a question, right? Yes! It is."; String delims = "[ .,?!]+"; String tokens = str.split(delims);
All we had to do was list all the delimiter characters inside the square brackets ( [ ] ).
Suppose we are representing arithmetic expressions using strings and wish to parse out the operands (that is, use the arithmetic operators as delimiters). The arithmetic operators that we will allow are addition (+), subtraction (-), multiplication (*), division (/), and exponentiation (^) and we will not allow parentheses (to make it a little simpler). This situation is not as straight-forward as it might seem. There are several characters that have a special meaning when they appear inside [ ]. The characters are ^ - [ and two &s in a row(&&). In order to use one of these characters, we need to put \\ in front of the character:
String expr = "2*x^3 - 4/5*y + z^2"; String delims = "[+\\-*/\\^ ]+"; // so the delimiters are: + - * / ^ space String tokens = expr.split(delims);
String s = string_to_parse; String delims = "[delimiters]+"; // use + to treat consecutive delims as one; // omit to treat consecutive delims separately String tokens = s.split(delims);