Instance variables in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an instance variable in Java?

An instance variable is a variable declared inside a class but outside any method, constructor, or block. Each object of the class has its own copy of the instance variable.

intermediate

Where are instance variables stored in memory?

Instance variables are stored in the heap memory as part of the object they belong to.

beginner

How do instance variables differ from static variables?

Instance variables belong to objects and each object has its own copy. Static variables belong to the class itself and are shared among all objects.

beginner

Can instance variables have default values if not initialized?

Yes, instance variables have default values based on their type (e.g., 0 for int, null for objects) if not explicitly initialized.

beginner

Example: Identify the instance variable in this code snippet:<br><pre>class Car {<br>  String color;<br>  void setColor(String c) {<br>    color = c;<br>  }<br>}</pre>

The instance variable is <code>color</code>. It is declared inside the class but outside any method, so each Car object has its own color.

What does each object of a class have regarding instance variables?

A Its own copy of instance variables

B Shares instance variables with other objects

C No instance variables

D Only static variables

Each object has its own copy of instance variables, so changes in one object do not affect others.

Where are instance variables declared in Java?

A Inside methods

B Inside the class but outside methods

C Outside the class

D Inside constructors only

Instance variables are declared inside the class but outside any method or constructor.

What is the default value of an uninitialized instance variable of type int?

A undefined

B null

C 0

D 1

Instance variables of type int default to 0 if not initialized.

Which memory area stores instance variables?

A Heap

B Stack

C Method area

D Register

Instance variables are stored in the heap as part of the object.

How do instance variables differ from static variables?

A Instance variables are shared; static are unique

B Both are the same

C Static variables are stored in heap; instance in stack

D Instance variables belong to objects; static belong to class

Instance variables belong to each object separately; static variables belong to the class and are shared.

Explain what instance variables are and how they behave in Java objects.

Think about how each object keeps its own data separate.

Describe the difference between instance variables and static variables in Java.

Consider who owns the variable: the object or the class.