What this deck covers
This deck focuses on Wrapper Classes, giving you a quick way to review the definitions, rules, and examples that matter most for AP Computer Science a.
AP Computer Science a Flashcards: Wrapper Classes
Study Wrapper Classes in AP Computer Science a with focused flashcards that help you recognize the idea, recall the key rule, and apply it in practice-style prompts.
AP Computer Science a
Wrapper Classes
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QUESTION
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What is the wrapper class for the primitive type boolean?
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ANSWER
Boolean. Direct correspondence between boolean primitive and Boolean wrapper.
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All flashcards
Flashcard 1: What is the wrapper class for the primitive type boolean?
Answer: Boolean. Direct correspondence between boolean primitive and Boolean wrapper.
Flashcard 2: Identify unboxing in: int num = new Integer(10);
Answer: Integer object is unboxed to int. Wrapper object is automatically unwrapped to primitive type.
Flashcard 3: Identify the wrapper class for the primitive type float.
Answer: Float. Direct correspondence between float primitive and Float wrapper.
Flashcard 4: What is the result of Character.toUpperCase('a')?
Answer: 'A'. Converts lowercase 'a' to uppercase 'A'.
Flashcard 5: What is the result of Integer.compare(4, 5)?
Answer: -1. Returns negative since 4 is less than 5.
Flashcard 6: How do you get the int value from a String '123'?
Answer: Integer.parseInt("123"). Parses string to extract integer value.
Flashcard 7: How do you convert an Integer object to int?
Answer: IntegerObject.intValue(). Returns primitive int value from wrapper object.
Flashcard 8: Convert double 3.14 to its wrapper class object.
Answer: Double.valueOf(3.14). Uses valueOf() to create wrapper object from primitive.
Flashcard 9: Which method converts a Double object to double?
Answer: DoubleObject.doubleValue(). Returns primitive double value from wrapper object.
Flashcard 10: How do you convert Integer to String?
Answer: Integer.toString(). Converts Integer wrapper object to string representation.
Flashcard 11: What is the purpose of a wrapper class in Java?
Answer: To provide object equivalents for primitive data types. Allows primitives to be used in collections and as objects.
Flashcard 12: Identify autoboxing in: List list = new ArrayList<>(); list.add(5);
Answer: int 5 is autoboxed to Integer. Primitive int is automatically wrapped to fit Integer collection.
Flashcard 13: Identify unboxing in: int num = new Integer(10);
Answer: Integer object is unboxed to int. Wrapper object is automatically unwrapped to primitive type.
Flashcard 14: What does Long.parseLong("123456789") return?
Answer: 123456789L. Parses string to extract long value.
Flashcard 15: Which wrapper class corresponds to the primitive type char?
Answer: Character. Direct correspondence between char primitive and Character wrapper.
Flashcard 16: What is the result of Character.toUpperCase('a')?
Answer: 'A'. Converts lowercase 'a' to uppercase 'A'.
Flashcard 17: How do you convert an Integer object to int?
Answer: IntegerObject.intValue(). Returns primitive int value from wrapper object.
Flashcard 18: How do you get the int value from a String '123'?
Answer: Integer.parseInt("123"). Parses string to extract integer value.
Flashcard 19: How do you convert Boolean object to String?
Answer: BooleanObject.toString(). Converts Boolean object to its string representation.
Flashcard 20: Which method converts a String 'true' to a boolean?
Answer: Boolean.parseBoolean("true"). Parses string to extract boolean value.
Flashcard 21: Which wrapper class represents the primitive type int?
Answer: Integer. Direct correspondence between int primitive and Integer wrapper.
Flashcard 22: Which method converts String '5' to Integer?
Answer: Integer.valueOf("5"). Creates Integer wrapper object from string representation.
Flashcard 23: What is unboxing in Java?
Answer: Automatic conversion of wrapper class to primitive. Java automatically unwraps wrapper objects when needed.
Flashcard 24: Convert double 3.14 to its wrapper class object.
Answer: Double.valueOf(3.14). Uses valueOf() to create wrapper object from primitive.
Flashcard 25: Find the error: Integer i = new Integer("abc");
Answer: Throws NumberFormatException. Invalid string format cannot be converted to number.
Flashcard 26: Which method checks if a Character is a digit?
Answer: Character.isDigit(). Checks if character represents a numeric digit (0-9).
Flashcard 27: What is the purpose of a wrapper class in Java?
Answer: To provide object equivalents for primitive data types. Allows primitives to be used in collections and as objects.
Flashcard 28: Identify the wrapper class for the primitive type double.
Answer: Double. Direct correspondence between double primitive and Double wrapper.
Flashcard 29: What is autoboxing in Java?
Answer: Automatic conversion of primitive to wrapper class. Java automatically wraps primitives when needed.
Flashcard 30: How do you convert Boolean object to String?
Answer: BooleanObject.toString(). Converts Boolean object to its string representation.
Flashcard 31: Identify the wrapper class for the primitive type double.
Answer: Double. Direct correspondence between double primitive and Double wrapper.
Flashcard 32: Which method converts a Double object to double?
Answer: DoubleObject.doubleValue(). Returns primitive double value from wrapper object.
Flashcard 33: Which wrapper class has the method parseShort(String)?
Answer: Short. Short wrapper class provides parseShort() static method.
Flashcard 34: What is the wrapper class for the primitive type boolean?
Answer: Boolean. Direct correspondence between boolean primitive and Boolean wrapper.
Flashcard 35: How do you convert a String '3.14' to double?
Answer: Double.parseDouble("3.14"). Parses string to extract double value.
Flashcard 36: What method converts float to Float wrapper object?
Answer: Float.valueOf(float). Creates Float wrapper object from primitive float.
Flashcard 37: What is autoboxing in Java?
Answer: Automatic conversion of primitive to wrapper class. Java automatically wraps primitives when needed.
Flashcard 38: How do you convert a String '3.14' to double?
Answer: Double.parseDouble("3.14"). Parses string to extract double value.
Flashcard 39: Which method returns the byte value of an Integer?
Answer: IntegerObject.byteValue(). Converts Integer to byte primitive type.
Flashcard 40: What is the result of Boolean.compare(true, false)?
Answer:
Flashcard 41: What is unboxing in Java?
Answer: Automatic conversion of wrapper class to primitive. Java automatically unwraps wrapper objects when needed.
Flashcard 42: Which method returns the byte value of an Integer?
Answer: IntegerObject.byteValue(). Converts Integer to byte primitive type.
Flashcard 43: How do you convert Integer to String?
Answer: Integer.toString(). Converts Integer wrapper object to string representation.
Flashcard 44: Which method returns the int value of a Byte object?
Answer: ByteObject.intValue(). Converts Byte wrapper to int primitive type.
Flashcard 45: What is the wrapper class for primitive type byte?
Answer: Byte. Direct correspondence between byte primitive and Byte wrapper.
Flashcard 46: Which method returns the int value of a Byte object?
Answer: ByteObject.intValue(). Converts Byte wrapper to int primitive type.
Flashcard 47: Convert int 5 to its wrapper class object.
Answer: Integer.valueOf(5). Uses valueOf() to create wrapper object from primitive.
Flashcard 48: What does Long.parseLong("123456789") return?
Answer: 123456789L. Parses string to extract long value.
Flashcard 49: Convert int 5 to its wrapper class object.
Answer: Integer.valueOf(5). Uses valueOf() to create wrapper object from primitive.
Flashcard 50: What method converts float to Float wrapper object?
Answer: Float.valueOf(float). Creates Float wrapper object from primitive float.
Flashcard 51: Which wrapper class corresponds to the primitive type char?
Answer: Character. Direct correspondence between char primitive and Character wrapper.
Flashcard 52: What method converts a Character object to char?
Answer: CharacterObject.charValue(). Returns primitive char value from wrapper object.
Flashcard 53: What is the result of Integer.compare(4, 5)?
Answer: -1. Returns negative since 4 is less than 5.
Flashcard 54: Which method checks if a Character is a digit?
Answer: Character.isDigit(). Checks if character represents a numeric digit (0-9).
Flashcard 55: Which method converts String '5' to Integer?
Answer: Integer.valueOf("5"). Creates Integer wrapper object from string representation.
Flashcard 56: What is the result of Boolean.compare(true, false)?
Answer:
Flashcard 57: Which method converts a String 'true' to a boolean?
Answer: Boolean.parseBoolean("true"). Parses string to extract boolean value.
Flashcard 58: Identify autoboxing in: List list = new ArrayList<>(); list.add(5);
Answer: int 5 is autoboxed to Integer. Primitive int is automatically wrapped to fit Integer collection.
Flashcard 59: Identify the wrapper class for the primitive type float.
Answer: Float. Direct correspondence between float primitive and Float wrapper.
Flashcard 60: Which wrapper class represents the primitive type int?
Answer: Integer. Direct correspondence between int primitive and Integer wrapper.
Flashcard 61: What method converts a Character object to char?
Answer: CharacterObject.charValue(). Returns primitive char value from wrapper object.
Flashcard 62: How do you convert '123.45' to Float?
Answer: Float.parseFloat("123.45"). Parses string to extract float value as Float object.
Flashcard 63: Find the error: Integer i = new Integer("abc");
Answer: Throws NumberFormatException. Invalid string format cannot be converted to number.