Questions and Answers
What is a wrapper class?
Wrapper classes in Java are mutable.
False
What are primitive data types?
Data types that are not created from classes and do not have attributes or methods.
What does the character class do?
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The method boolean isDigit(char ch) returns true for characters other than digits.
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What does the method boolean isLetter(char ch) check?
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What does the method boolean isSpaceChar(char ch) tell us?
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What is the purpose of the method char toLowerCase(char ch)?
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What does the valueOf method do?
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The StringBuilder class allows its objects to be modified.
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What does the method trim() do?
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When tokenizing a string, it is unnecessary to trim it beforehand.
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What is autoboxing?
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What is unboxing?
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What is a delimiter?
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What is the file extension used for a comma-separated value file?
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Study Notes
Wrapper Classes
- Wrapper classes are classes that encapsulate primitive data types, allowing the creation of objects instead of just variables.
- They provide methods to perform operations related to the encapsulated primitive type and are immutable.
- Java defines wrapper classes for each primitive data type, including Byte, Double, Float, Integer, Long, and Short.
Primitive Data Types
- Primitive data types are basic data types that are not objects and do not possess attributes or methods.
- These types include byte, double, float, int, long, and short.
Character Class
- The Character Class serves as a wrapper for the char data type and offers methods for character testing and conversion.
Character Testing Methods
-
isDigit(char ch)
: Checks if the character is a digit (0-9). -
isLetter(char ch)
: Verifies if the character is an alphabetic letter. -
isLetterOrDigit(char ch)
: Returns true for characters that are either digits or letters. -
isLowerCase(char ch)
: Checks if the character is a lowercase letter. -
isUpperCase(char ch)
: Checks if the character is an uppercase letter. -
isSpaceChar(char ch)
: Identifies if the character is a space character. -
isWhiteSpace(char ch)
: Identifies if the character is any whitespace character (space, tab, newline).
String Manipulation Methods
-
substring(int start)
: Extracts a substring from a specified starting index to the end of the string. -
substring(int start, int end)
: Returns a substring from start to end (end is exclusive). -
concat(String str)
: Combines the contents of the calling string with another string. -
trim()
: Eliminates leading and trailing whitespace characters.
String Search Methods
-
indexOf(char ch)
: Locates the first occurrence of a character within the string, returning its index or -1 if not found. -
lastIndexOf(char ch)
: Finds the last occurrence of a character, searching from the end of the string.
String Comparison Methods
-
startsWith(String str)
: Verifies if the string begins with the specified prefix. -
endsWith(String str)
: Confirms if the string ends with the specified suffix. -
regionMatches(...)
: Compares specific regions of two strings for equality.
StringBuilder and StringBuffer
- The StringBuilder class allows modification of string contents and provides additional methods compared to String.
- StringBuffer methods are synchronized for thread safety, while StringBuilder methods are not.
Tokenization
- Tokenizing is the act of breaking a string into components called tokens, often using the String class's
split
method. - The delimiter is a character that separates tokens.
Regular Expressions
- Regular expressions specify patterns of characters and can be used to search for those patterns within strings and other text collections.
Autoboxing and Unboxing
- Autoboxing is the automatic conversion of primitive values into their corresponding wrapper objects.
- Unboxing is the reverse process, converting wrapper objects back into their primitive types.
Static Members and Constants
-
MIN_VALUE
andMAX_VALUE
are static final variables representing the minimum and maximum values for respective data types.
CSV File Format
- Comma Separated Value (CSV) format is used when exporting data from Excel, where rows correspond to lines and cell values are delineated by commas.
- Files saved in this format use the .csv extension.
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Description
Test your knowledge on Wrapper Classes as discussed in Chapter 9 of 'Text Processing and More about Wrapper Classes'. This quiz dives into the definitions, uses, and characteristics of wrapper classes in Java. Perfect for reinforcing your understanding of these essential programming concepts.