The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
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java.util.regex
package? Describe the purpose of each.
Answer:
Pattern
instances are compiled representations of regular expressions.Matcher
instances are engines that interpret patterns and perform match operations against input strings.PatternSyntaxException
defines an unchecked exception indicating a syntax error in a regular expression."foo"
. What is the start index? What is the end index? Explain what these numbers mean.
Answer: Each character in the string resides in its own cell. Index positions point between cells. The string "foo"
starts at index 0 and ends at index 3, even though the characters only occupy cells 0, 1, and 2.
Answer: An ordinary character in a regular expression matches itself. A metacharacter is a special character that affects the way a pattern is matched. The letter A
is an ordinary character. The punctuation mark .
is a metacharacter that matches any single character.
Answer: There are two ways:
\
);\Q
(at the beginning) and \E
(at the end).Answer: This is a character class. It matches any single character that is in the class of characters specified by the expression between the brackets.
\d
, \s
, and \w
. Describe each one, and rewrite it using square brackets.
Answer:
\d |
Matches any digit. | [0-9] |
\s |
Matches any white space character. | [ \t\n-x0B\f\r] |
\w |
Matches any word character. | [a-zA-Z_0-9] |
\d
, \s
, and \w
, write two simple expressions that match the opposite set of characters.
Answer:
\d |
\D |
[^\d] |
\s |
\S |
[^\s] |
\w |
\W |
[^\w] |
(dog){3}
. Identify the two subexpressions. What string does the expression match?
Answer: The expression consists of a capturing group, (dog)
, followed by a greedy quantifier {3}
. It matches the string "dogdogdog".
Solution: ([A-Z][a-zA-Z]*)\s\1