Arrays and Strings - Beginning Java 2 SDK - page 141

Checking the Start and End of a String
It can be useful to be able to check just part of a string. You can test whether a string starts with a
particular character sequence by using the method startsWith() . If string1 has been defined as
" Too many cooks ", the expression string1.startsWith("Too") will have the value true . So
would the expression string1.startsWith("Too man") . The comparison is case sensitive so the
expression string1.startsWith("tOO") will be false .
A complementary method endsWith() checks for what appears at the end of a string, so the expression
string1.endsWith("cooks") will have the value true . The test is case sensitive here, too.
Sequencing Strings
You will often need to place strings in order, for example, when you have a collection of names. Testing
for equality doesn't help - what you need is the method compareTo() in the class String . This
method compares the String object from which it is called with the argument passed to it, and returns
an integer which is negative if the String object is less than the argument passed, zero if the S tring
object is equal to the argument, and positive if the String object is greater than the argument. It is not
that obvious what the terms 'less than', 'equal to', and 'greater than' mean when applied to strings, so
let's define that a bit more precisely.
Two strings are compared in the compareTo() method by comparing successive corresponding
characters, starting with the first character in each string. The process continues until a pair of
corresponding characters are found to be different, or the last character in the shortest string is reached.
Individual characters are compared by comparing their Unicode representations - so two characters are
equal if the numeric values of their Unicode representations are equal. One character is greater than
another if the numerical value of its Unicode representation is greater than that of the other.
One string is greater than another if it has a character greater than the corresponding character in the
other string, and all the previous characters were equal. So if string1 has the value " mad dog ", and
string2 has the value " mad cat ", then the expression:
string1.compareTo(string2)
will return a positive value as a result of comparing the fifth characters in the strings: the ' d ' in string1
with the ' c ' in string2 .
What if the corresponding characters in both strings are equal up to the end of the shorter string, but the
other string has more characters? In this case the longer string is greater than the shorter string, so
" catamaran " is greater than " cat ".
One string is less than another string if it has a character less than the corresponding character in the other
string, and all the preceding characters are equal. Thus the following expression will return a negative value:
string2.compareTo(string1)
Two strings are equal if they contain the same number of characters and corresponding characters are
identical. In this case the compareTo() method returns 0.
We can exercise the compareTo() method in a simple example.