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Questions and Answers
Which method is used to convert a String to an int in Java?
Wrapper classes in Java allow primitive data types to be treated as objects.
True
What is the process of converting a primitive type to its corresponding wrapper class called?
Autoboxing
The wrapper class for the primitive data type 'double' is called ____.
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Match the following primitive data types with their corresponding wrapper classes:
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What is the process of converting a primitive data type to its corresponding wrapper class called?
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Unboxing refers to the conversion of a primitive type into a wrapper class.
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What is the wrapper class for the primitive type 'char'?
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The automatic conversion of a wrapper type into its corresponding _____ type is known as unboxing.
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Match each primitive type with its corresponding wrapper class:
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Study Notes
Primitive Types and Wrapper Classes
- Java has primitive data types that each have a corresponding wrapper class, enabling the treatment of primitives as objects.
- Wrapper classes:
- boolean → Boolean
- char → Character
- byte → Byte
- short → Short
- int → Integer
- long → Long
- float → Float
- double → Double
Auto Boxing
- Auto boxing is the automatic conversion of primitive types to their respective wrapper classes.
- Example:
- Converting
int
toInteger
- Statement:
Integer j = a;
triggers the compiler to performInteger.valueOf(a)
internally.
- Converting
Unboxing
- Unboxing is the reverse of auto boxing, converting wrapper types back to their primitive counterparts.
- Example:
- Explicit casting demonstrated in a conversion from
double
toint
.
- Explicit casting demonstrated in a conversion from
Type Conversion in Java
- Type conversion refers to changing data from one type to another, known as type casting or coercion.
- Java allows conversions for both primitive and reference types.
String to Primitive Conversions
-
String to int:
- Use
Integer.parseInt(String numberString)
, e.g., from"123"
to123
.
- Use
-
int to String:
- Use
String.valueOf(int number)
, e.g., converting123
to"123"
.
- Use
-
String to double:
- Use
Double.parseDouble(String numberString)
, e.g., from"10.5"
to10.5
.
- Use
Wrapper Classes
- Wrapper classes enable treating primitive data types as objects.
- Useful for converting primitive types into objects for scenarios requiring objects.
- Only one copy of each class variable exists and is shared among all instances of the class.
Class Variables
- Class variables are initialized with default values if not assigned explicitly.
- Accessed without creating an instance of the class, using the class name directly.
- Example demonstrates accessing class variable
count
.
Type Casting
- Type casting is the process of converting values between different data types.
- Two types of casting:
-
Implicit Casting (Widening): Automatic conversion from a smaller to a larger data type, e.g.,
int
todouble
. -
Explicit Casting (Narrowing): Manual conversion from a larger to a smaller data type, e.g.,
double
toint
, requiring explicit syntax.
-
Implicit Casting (Widening): Automatic conversion from a smaller to a larger data type, e.g.,
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Description
Test your knowledge on Java's primitive types and their corresponding wrapper classes. This quiz will cover the essential data types in Java, helping you understand the relationships between them and their functionalities. Perfect for beginners and intermediate learners!