Autoboxing in Java - Cheat Sheet & Quick Revision

overview

Recall & Review

beginner

What is autoboxing in Java?

Autoboxing is the automatic conversion Java does between primitive types (like int) and their corresponding wrapper classes (like Integer). It helps you use primitives as objects without manual conversion.

beginner

Which wrapper class corresponds to the primitive type <code>double</code>?

The wrapper class for the primitive type <code>double</code> is <code>Double</code>.

beginner

What happens when you assign an int value to an Integer variable?

Java automatically converts the int primitive to an Integer object using autoboxing.

beginner

Explain unboxing in Java.

Unboxing is the automatic conversion from a wrapper class object (like <code>Integer</code>) back to its primitive type (like <code>int</code>).

beginner

Why is autoboxing useful in Java?

Autoboxing lets you write cleaner code by automatically converting between primitives and objects. This is helpful when using collections like ArrayList that only work with objects.

What does autoboxing do in Java?

A Converts strings to numbers

B Automatically converts primitives to wrapper objects

C Converts objects to strings

D Automatically converts wrapper objects to primitives

Which of these is a wrapper class for the primitive type boolean?

A BoolClass

B Bool

C Boolean

D booleanWrapper

What happens if you assign an Integer object to an int variable?

A Unboxing converts Integer to int automatically

B Compilation error

C Runtime error

D The Integer object is stored as is

Which of these collections can only hold objects, not primitives?

A LinkedList of primitives

B int[]

C double[]

D ArrayList

Which Java feature was introduced to simplify working with primitives and wrapper classes?

A Autoboxing and unboxing

B Generics

C Lambda expressions

D Annotations

Describe autoboxing and unboxing in Java and give an example of each.

Why is autoboxing important when using Java collections like ArrayList?