Java Primitive Types and Wrapper Classes

Questions and Answers

Which method is used to convert a String to an int in Java?

String.valueOf()

Double.parseDouble()

String.toInt()

Integer.parseInt() (correct)

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 ____.

Double Signup and view all the answers

Match the following primitive data types with their corresponding wrapper classes:

int = Integer double = Double char = Character boolean = Boolean Signup and view all the answers

What is the process of converting a primitive data type to its corresponding wrapper class called?

Auto boxing Signup and view all the answers

Unboxing refers to the conversion of a primitive type into a wrapper class.

False Signup and view all the answers

What is the wrapper class for the primitive type 'char'?

Character Signup and view all the answers

The automatic conversion of a wrapper type into its corresponding _____ type is known as unboxing.

primitive Signup and view all the answers

Match each primitive type with its corresponding wrapper class:

int = Integer boolean = Boolean float = Float double = Double Signup and view all the answers

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 to Integer
- Statement: Integer j = a; triggers the compiler to perform Integer.valueOf(a) internally.

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 to int.

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" to 123.
int to String:
- Use String.valueOf(int number), e.g., converting 123 to "123".
String to double:
- Use Double.parseDouble(String numberString), e.g., from "10.5" to 10.5.

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 to double.
- Explicit Casting (Narrowing): Manual conversion from a larger to a smaller data type, e.g., double to int, requiring explicit syntax.

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!