Java String Methods Quiz

Chapter 14: Strings, Characters, and Regular Expressions

• This chapter discusses strings, StringBuilder, and Character classes from the java.lang package
• These classes provide the foundation for string and character manipulation in Java
• The chapter also covers regular expressions to validate input data for applications

14.1 Introduction

• This chapter discusses String, StringBuilder, and Character classes from the java.lang package
• These classes form the basis for string and character manipulation in Java
• Regular expressions are also covered, enabling input validation

14.2 Fundamentals of Characters and Strings

• Programs use character literals (represented in single quotes)
• The value of a character literal corresponds to its Unicode integer value
• String literals are sequences of characters enclosed in double quotes and are stored in memory as String objects

14.3 Class String

• String represents strings in Java
• Subsequent sections detail String class capabilities

14.3.1 String Constructors

• A no-argument constructor creates an empty string with length 0
• A constructor taking a String object copies the argument
• A constructor taking a char array creates a String from the array's characters
• A constructor taking a char array and two integers creates a String from a specified portion of the array

14.3.2 String Methods length, charAt, and getChars

• The length method returns the number of characters in a string
• The charAt method returns the character at a specific index
• The getChars method copies characters from a String into a char array

14.3.3 Comparing Strings

• Strings are compared using the numeric codes of their constituent characters
• Methods equals, equalsIgnoreCase, compareTo, regionMatches, and the == operator are used to compare String objects

14.3.4 Locating Characters and Substrings in Strings

• Methods indexOf and lastIndexOf locate characters or substrings within a string
• These methods enable searching for specific characters or substrings.
• Versions exist to search starting at a specific index or allowing case-insensitive comparisons.

14.3.5 Extracting Substrings from Strings

• Strings offer substring methods to copy portions into new String objects
• One integer argument for substring specifies the starting index
• Two integer arguments indicate the start and end indices (exclusive) to extract from the original string

14.3.6 Concatenating Strings

• The concat method concatenates two String objects, returning a new String object composed of characters from both
• The original strings remain unchanged

14.3.7 Miscellaneous String Methods

• The replace method returns a new string with characters replaced accordingly. There are overloads to replace substrings
• The toUpperCase method converts a string to uppercase
• The toLowerCase method converts a string to lowercase
• The trim method removes leading/trailing whitespace characters
• The toCharArray method returns a character array containing a copy of the string's characters

14.3.8 String Method valueof

• Static valueOf methods convert various data types (including primitives and objects) to String objects

14.4 Class StringBuilder

• StringBuilder creates and manipulates modifiable strings
• StringBuilders have capacities that expand as needed to store characters exceeding the initial capacity

14.4.1 StringBuilder Constructors

• A no-argument constructor creates an empty StringBuilder with an initial capacity of 16.
• A constructor with an integer argument creates an empty StringBuilder with the specified capacity.
• A constructor with a String argument creates a StringBuilder containing the String's characters and a capacity of that plus 16.
• The toString() method returns the StringBuilder’s content as a String.

14.4.2 StringBuilder Methods length, capacity, setLength, and ensureCapacity

• The length method returns the current number of characters in the StringBuilder
• The capacity method returns the maximum number of characters the StringBuilder can store without reallocating memory.
• The ensureCapacity method guarantees that the StringBuilder has at least the specified capacity.
• The setLength method increases or decreases the StringBuilder's length.

14.4.3 StringBuilder Methods charAt, setCharAt, getChars, and reverse

• The charAt method returns the character at a given index
• The setCharAt method sets a character at a given index
• The getChars method copies the characters into another char array, taking the start and end indices plus the destination char array and offset as input
• The reverse() method reverses the order of characters in the StringBuilder

14.4.4 StringBuilder append Methods

• Overloaded append methods add various data types to the end of the StringBuilder
• These methods include versions for primitives, char arrays, Strings, and objects

14.4.5 StringBuilder Insertion and Deletion Methods

• Overloaded insert methods insert values at any position
• Methods delete and deleteCharAt remove characters from specific or sequential positions

14.5 Class Character

• The Character class provides static methods for convenience in operations with individual characters
• Methods like isDefined, isDigit, isLetter, etc., determine character properties based on the Unicode character set

14.6 Tokenizing Strings

• String tokenization divides strings into smaller units called tokens.
• Methods like split break a String into tokens, returning an array of String-based tokens.
• Space, tab, newline and carriage return characters commonly separate tokens

14.7 Regular Expressions, Class Pattern, and Class Matcher

• Regular expressions define patterns for matching characters in larger Strings.
• Useful for input validation and compiler construction
• Methods matches, replaceAll, and replaceFirst are part of the regular expression support

14.7 (cont.) Character Classes

• Character classes define sets of characters for matching.
• Predefined classes like \d, \w, and \s represent digits, word characters, and whitespace, respectively, in regular expressions

14.7 (cont.) Character Ranges

• Character ranges can be used with regular expression character classes to represent groups of characters based on their Unicode values

14.7 (cont.) Quantifiers

• Quantifiers like *, +, ?, {} in regular expressions control the number of occurrences to match
• These match zero or more (*), one or more (+), zero or one (?), or a specific number ({}) of instances

14.7 (cont.) Regular Expressions and Methods

• Classes Pattern and Matcher are used for more complex regular expression operations
• Methods matches, replace, and split in the String class and Matcher class use regular expressions to modify or analyze strings