Instance variable

<h2 id="examples">Examples</h2>
<h3>C++</h3>
struct Request {

static int count1; // variable name is not important
    int number;

Request() {
        number = count1; // modifies the instance variable "this->number"
        ++count1; // modifies the class variable "Request::count1"
    }

};

int Request::count1 = 0;

<p>In this <a href="/facts/C%2B%2B/Et0F2qn9">C++</a> example, the instance variable Request::number is a copy of the <a href="/facts/Class_variable/H5b1PUyR">class variable</a> Request::count1 where each instance constructed is assigned a sequential value of count1 before it is <a href="/facts/Increment_operator/3e4cEouw">incremented</a>. Since number is an instance variable, each Request object contains its own distinct value; in contrast, there is only one object Request::count1 available to all class instances with the same value.
</p>
<h3>Java</h3>
//Example.java

class Example {
    public int x = 0;
    
    public void setX(int newValue) {
        this.x = newValue;
    }
}

//Main.java

class Main {
    public static void main(String[] args) {
        Example example1 = new Example();
        Example example2 = new Example();
        
        //We can set the value of x by itself, as the variable is public
        example1.x = 10;
        
        assert example1.x == 10;
        assert example2.x ==  0;
        
        //As setX is an instance method, it can also access the variable
        example2.setX(-10);
        
        assert example1.x ==  10;
        assert example2.x == -10;
    }
}

<p>In this <a href="/facts/Java_(programming_language)/9ScgFyAL">Java</a> example, we can see how instance variables can be modified in one instance without affecting another.
</p>
<h3>Python</h3>
class Dog:
    def __init__(self, breed):
        self.breed = breed # instance variable

# dog_1 is an object
# which is also an instance of the Dog class
dog_1 = Dog("Border Collie")
<p>In the above <a href="/facts/Python_(programming_language)/YbuGqofa">Python</a> code, the instance variable is created when an argument is parsed into the instance, with the specification of the breed positional argument.
</p>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"Instance Variables in C++ Programming". Dremendo. Retrieved 2024-03-08. <a href="https://www.dremendo.com/cpp-programming-tutorial/cpp-instance-variables" target="_blank">https://www.dremendo.com/cpp-programming-tutorial/cpp-instance-variables</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"Java Variables". GeeksforGeeks. 2017-02-06. Retrieved 2024-03-08. <a href="https://www.geeksforgeeks.org/variables-in-java/" target="_blank">https://www.geeksforgeeks.org/variables-in-java/</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"The Java Tutorial, Variables". docs.oracle.com. Oracle. Archived from the original on 23 October 2014. Retrieved 23 October 2014. <a href="https://web.archive.org/web/20141023153904/http://docs.oracle.com/javase/tutorial/java/nutsandbolts/variables.html" target="_blank">https://web.archive.org/web/20141023153904/http://docs.oracle.com/javase/tutorial/java/nutsandbolts/variables.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>"Difference between Instance Variable and Class Variable". GeeksforGeeks. 2021-04-26. Retrieved 2024-03-08. <a href="https://www.geeksforgeeks.org/difference-between-instance-variable-and-class-variable/" target="_blank">https://www.geeksforgeeks.org/difference-between-instance-variable-and-class-variable/</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>"The Java Tutorials, Understanding Class Members". docs.oracle.com. Oracle. Archived from the original on 11 October 2014. Retrieved 23 October 2014. <a href="https://web.archive.org/web/20141011000515/http://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html" target="_blank">https://web.archive.org/web/20141011000515/http://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Matuszek, David. "Static". cis.upenn.edu. University of Pennsylvania. Archived from the original on 23 October 2014. Retrieved 23 October 2014. <a href="https://web.archive.org/web/20141023160745/http://www.cis.upenn.edu/~matuszek/General/JavaSyntax/static.html" target="_blank">https://web.archive.org/web/20141023160745/http://www.cis.upenn.edu/~matuszek/General/JavaSyntax/static.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
</ol>

Instance variable open-in-new

Instance variable