18 Questions
What do regular expressions represent?
A character or a sequence of characters
Which package in Java provides classes for working with regular expressions?
java.util.regex
What is the purpose of using regular expressions in form validation?
To check for correct email format
What is the difference between the matches() method and the equals() method in Java?
The matches() method allows for variability, while the equals() method compares a single string
What is the purpose of the | symbol in the regular expression 'cat|dog'?
To allow for multiple values to be matched
What is the name of the method in the String class that uses regular expressions to check if a string matches a given pattern?
matches()
What is the purpose of the compile method in the Pattern class?
To initialize a pattern of characters as defined by a regular expression
What is the function of the matches() method in the Matcher class?
To check if the regular expression given in the Pattern declaration matches a given string
What is the purpose of the find() method in the Matcher class?
To scan the input sequence looking for the next subsequence that matches the pattern
What is the function of the split() method in the Matcher class?
To split the string around matches of the given regular expression
What is the purpose of combining symbols in regular expressions?
To create a more flexible and powerful pattern
What is the purpose of the Matcher class in the java.util.regex package?
To store a possible match between a pattern and a string
What does the dot (.) represent in regular expressions?
Any single character
What does the statement return str.matches("A*"); do?
Returns true if str consists of zero or more A's
What is the purpose of regular expressions in string validation?
To allow for very powerful validation of strings without having to write much code
What does the matches(".*") method do?
Returns true if the string contains any characters
What is the purpose of the {x,y} syntax in regular expressions?
To specify a range of occurrences
What does the matches("[0-9].") statement do?
Returns true if the string consists of a number followed by any single character
Study Notes
Regular Expressions Fundamentals
- A regular expression (or regex) is a character or a sequence of characters that represent a string or multiple strings.
- Regular expressions are part of the java.util.regex package, which has classes to help form and use regular expressions.
- They allow for quicker, easier searching, parsing, and replacing of characters in a string.
- They are used to ensure that strings contain specific contents and are often used to check correct email format (@ sign is included) on form validation.
Methods and Classes
- The String class contains a method named matches(String regex) that returns true if a string matches the given regular expression.
- The Pattern class stores the format of a regular expression.
- The Matcher class stores a possible match between a pattern and a string.
- The compile method compiles the given regular expression into a pattern.
Pattern and Matcher
- A compiled regex pattern can speed up your program when the pattern is used frequently.
- The matcher method returns a Matcher object.
- The matches() method checks if the regular expression given in the Pattern declaration matches a given string.
RegEx Operations
- The find() method scans the input sequence looking for the next subsequence that matches the pattern.
- The split() method splits the string around matches of the given regular expression.
- The dot (.) is the wildcard operator that represents any single character in regular expressions.
Repetition Operators
-
- represents 0 or more occurrences.
- ? represents 0 or 1 occurrence.
-
- represents 1 or more occurrences.
- {x} represents x occurrences.
- {x,y} represents between x and y occurrences.
- {x,} represents x or more occurrences.
Examples
- return animal.matches("cat|dog"); checks if the string "animal" is "cat" or "dog".
- return str.matches(".?[0-5]{10}"); checks if the string "str" matches the specified pattern.
- return str.matches("A*"); returns true if str consists of zero or more A's but no other letter.
- return str.matches(".*"); returns true if str is a sequence of any number of any characters.
Learn about combining regular expression symbols, the Pattern class, and the Matcher class in Java. Understand how to compile regex patterns and their uses.
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