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Questions and Answers
Which of the following statements best describes a wrapper class?
Which of the following statements best describes a wrapper class?
Which package are all wrapper classes found in, in Java?
Which package are all wrapper classes found in, in Java?
Which of the following is NOT a valid primitive datatype and wrapper class pair?
Which of the following is NOT a valid primitive datatype and wrapper class pair?
What is a primary use of wrapper classes?
What is a primary use of wrapper classes?
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Which of the given functions can be used to determine if a given character is an uppercase letter?
Which of the given functions can be used to determine if a given character is an uppercase letter?
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If Character.isLowerCase('A') is executed, what would be the return value?
If Character.isLowerCase('A') is executed, what would be the return value?
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What does the method Character.toUpperCase() do?
What does the method Character.toUpperCase() do?
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What is the return type of method Character.isDigit()?
What is the return type of method Character.isDigit()?
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What does the Character.isLetterOrDigit() method return if the character is a space?
What does the Character.isLetterOrDigit() method return if the character is a space?
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Which Character method would you use to determine if a given character is a numerical digit?
Which Character method would you use to determine if a given character is a numerical digit?
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If a character variable c holds the value '7', what will Character.isLetter(c) return?
If a character variable c holds the value '7', what will Character.isLetter(c) return?
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What is the result of calling Character.toUpperCase(c) if character c is already an uppercase letter?
What is the result of calling Character.toUpperCase(c) if character c is already an uppercase letter?
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Which of the following condition will return true for a lowercase letter c?
Which of the following condition will return true for a lowercase letter c?
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What does Character.isWhitespace() return for the character '\t'?
What does Character.isWhitespace() return for the character '\t'?
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If c is the character 'b', what will Character.toUpperCase(c) return?
If c is the character 'b', what will Character.toUpperCase(c) return?
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What will Character.toLowerCase() return if c is the character '5'?
What will Character.toLowerCase() return if c is the character '5'?
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Study Notes
Wrapper Classes in Java
- Wrapper classes act as containers for primitive data types, allowing them to be treated as objects.
- Each primitive type (e.g., int, char, float) has a corresponding wrapper class (e.g., Integer, Character, Float).
- Wrapper classes are located in the
java.langpackage. - Wrapper classes provide methods for converting between primitive types and object types.
- They allow for operations that are not available with primitive types. This includes string conversions to numbers or vice versa. They can also determine the nature of data.
Primitive and Wrapper Classes and their Conversions
- Primitive types are basic data types like
int,boolean,float, held directly in memory. - Wrapper classes are object types, encapsulating primitive values.
- Conversion between primitive types and their wrapper classes can occur through autoboxing (primitive to object) and unboxing (object to primitive).
Character Wrapper Class Functions
- Character class methods are static, allowing access using
Character.methodName(). - They all accept a single character (
char) parameter. - Many Character class methods return a boolean; this indicates if a condition is true or false based on the specific character input.
- Other Character class methods return a character (
char).
String to Number Conversion
-
Integer.parseInt(String): converts a string representing an integer to its integer value. -
Double.parseDouble(String): converts a string representing a double to its double value. -
Float.parseFloat(String): converts a string representing a float to its float value. -
Long.parseLong(String): converts a string representing a long to its long value.
Converting Numbers to Strings
-
String.valueOf(int)converts integers to strings. -
String.valueOfcan also convert any number type to its string equivalent.
Autoboxing and Unboxing
- Autoboxing: Automatically converting a primitive data type to its corresponding
Wrapperclass equivalent (e.g., int to Integer). - Unboxing: Automatically converting a
Wrapperclass object to its primitive data type equivalent (e.g., Integer to int).
Example Function Usage
-
Character.isUpperCase(char c): Checks if the input character is an uppercase letter, returningtrueorfalse. -
Character.isLowerCase(char c): Checks if the input character is a lowercase letter, returningtrueorfalse. -
Character.isDigit(char c): Checks if the input character is a digit, returningtrueorfalse. -
Character.isLetter(char c): Checks if the input character is a letter, returningtrueorfalse. -
Character.isLetterOrDigit(char c): Checks if the input character is a letter or a digit, returningtrueorfalse. -
Character.toUpperCase(char c): Returns the uppercase of the input character. -
Character.toLowerCase(char c): Returns the lowercase of the input character.
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Description
This quiz covers the fundamentals of wrapper classes in Java, exploring their role in object-oriented programming as containers for primitive data types. It delves into the concept of autoboxing and unboxing, along with specific functions related to character wrapper classes. Test your knowledge on the conversions and functionality of these essential classes.
