Unboxing in Java - Cheat Sheet & Quick Revision

overview

Recall & Review

beginner

What is unboxing in Java?

Unboxing is the automatic conversion of an object of a wrapper class (like Integer) to its corresponding primitive type (like int).

beginner

Which of these is an example of unboxing?

Integer num = 10;
int n = num;

Assigning an Integer object to an int variable automatically converts the Integer to int. This is unboxing.

beginner

Why is unboxing useful in Java?

Unboxing lets you use wrapper objects like primitive types without manually converting them, making code simpler and easier to read.

intermediate

What happens if you unbox a null wrapper object?

Unboxing a null wrapper object causes a NullPointerException because there is no primitive value to convert.

beginner

Which wrapper classes support unboxing in Java?

All wrapper classes like Integer, Double, Boolean, Character, Byte, Short, Long, and Float support unboxing to their respective primitive types.

What does unboxing do in Java?

A Converts a wrapper object to a primitive type automatically

B Converts a primitive type to a wrapper object automatically

C Converts a String to an int

D Converts an int to a String

What will happen if you try to unbox a null Integer object?

A It returns 0

B It returns null

C It throws a NullPointerException

D It converts to false

Which of these is an example of unboxing?

A Integer n = 5;

B int n = new Integer(5);

C int n = Integer.valueOf(5);

D int n = new Integer(5).intValue();

Which wrapper class does NOT support unboxing?

A String

B Double

C Integer

D Boolean

Unboxing helps to:

A Make code more complex

B Convert primitives to objects

C Prevent NullPointerExceptions

D Avoid manual conversion from wrapper to primitive

Explain what unboxing is and give a simple Java example.

What error can occur during unboxing and why?