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Instance Variable in Java

Instance variable in Java is used by Objects to store their states. Variables which are defined without the STATIC keyword and are Outside any method declaration are Object-specific and are known as instance variables. They are called so because their values are instance specific and are not shared among instances.

Example of Instance Variable

class Page {
public String pageName;
// instance variable with public access
private int pageNumber;
// instance variable with private access
}

Rules for Instance variable in Java

  • Instance variables can use any of the four access levels
  • They can be marked final
  • They can be marked transient
  • They cannot be marked abstract
  • They cannot be marked synchronized
  • They cannot be marked strictfp
  • They cannot be marked, native
  • They cannot be marked static

Cheatsheet

  • Public, Private, Protected all 3 access modifiers can be applied to Instance Variable(Default also).
  • Instance Variable can be marked final.
  • Instance Variable can be marked transient.
  • Instance Variables cannot be abstract.
  • Instance Variable cannot have a synchronized modifier.
  • Instance Variable cannot have a strictfp modifier.
  • Instance Variable cannot have the native modifier.
  • Instance Variable cannot have a Static modifier as it will become a Class level variable.
  • The instance variable will get default value, means instance variable can be used without initializing it. The same is not true for Local Variable.
Instance Variable TypeDefault Value
booleanfalse
byte(byte)0
short(short) 0
int0
long0L
charu0000
float0.0f
double0.0d
Objectnull
package com.jbt;

/*
 * Here we will discuss about different type of Variables available in Java
 */
public class VariablesInJava {

	/*
	 * Below variable is INSTANCE VARIABLE as it is outside any method and it is
	 * not using STATIC modifier with it. It is using default access modifier.
	 * To know more about ACCESS MODIFIER visit appropriate section
	 */
	int instanceField;

	/*
	 * Below variable is STATIC variable as it is outside any method and it is
	 * using STATIC modifier with it. It is using default access modifier. To
	 * know more about ACCESS MODIFIER visit appropriate section
	 */
	static String staticField;

	public void method() {
		/*
		 * Below variable is LOCAL VARIABLE as it is defined inside method in
		 * class. Only modifier that can be applied on local variable is FINAL.
		 * To know more about access and non access modifier visit appropriate
		 * section.
		 *
		 * Note* : Local variable needs to initialize before they can be used.
		 * Which is not true for Static or Instance variable.
		 */
		final String localVariable = "Initial Value";
		System.out.println(localVariable);
	}

	public static void main(String args[]) {
		VariablesInJava obj = new VariablesInJava();

		/*
		 * Instance variable can only be accessed by Object of the class only as below.
		 */
		System.out.println(obj.instanceField);

		/*
		 * Static field can be accessed in two way.
		 * 1- Via Object of the class
		 * 2- Via CLASS name
		 */
		System.out.println(obj.staticField);
		System.out.println(VariablesInJava.staticField);
                System.out.println(new VariablesInJava().instanceField);
	}
}

Get hold of Static Variable in Java to understand how it is different from the Instance variable.

References

Author avatar
JBT
https://javabeginnerstutorial.com/

60 comments

  1. shivaraj.j

    nice it is……..i want learn from this

  2. shivaraj.j

    nice it is……..i want learn from this ……….tihs is fist time i saw this……….

  3. RK

    Can be abstract – Could you explain what it means for an instance variable to be abstract

  4. nidhi paul

    Awesme xplanation
    thanx
    concept gt cleared
    keep up the good wrk *–*

  5. Bharatgpatel

    I want learned java

  6. Ramesh M

    You can’t declare an instance variable as abstract.The program wont compile.Please check

  7. Vishwanath T S

    Static variables can also be accessed directly:
    /*
    * Static field can be accessed in two way.
    * 1- Via Object of the class
    * 2- Via CLASS name
    *3-Directly calling the static variable itself(within static methods)
    */
    System.out.println(obj.staticField);
    System.out.println(VariablesInJava.staticField);
    System.out.println(staticField);

  8. shweta

    Hi Bharat,

    instance variable can be static but you have mention it cannot be static ..as per my knowledge its wrong statement.

    • kiran

      bharat: instance variables can’t be static ..if you define static variable just outside the method it can’t be instance variable….if you define variables with static keyword ..it becomes class variable(which is not instance variable..)..
      class variables are not part of Object.where as instance variables are part of Object..Object stores its state in Non Static fields i.e instance variables also called ‘fields’

    • karim

      no instance variable cannot be static because we have learned in the rules of the instance variable

  9. Tabish Khan

    @Shweta, sister, a variable declared as “static”, makes it a class variable, not an instance variable. There’s a small and a simple difference between the two. 🙂

  10. ashish

    what is the main use of constructor in java core.

  11. nupur

    You said instance variables can be abstract, but its not true, why we need to mark any variable abstract?!

  12. Sanjay Varma

    Instance variable can be access in this way too

    System.out.println(new VariablesInJava().instanceField)

    This is recommended when your calling Instance variable not more than once.

  13. Muaz Razaq

    Great Work, Nice Explaination, I Simply Understood The Difference

  14. Achyuth

    why don’t use the these keywords like Abstract,strictfp,native.

  15. shah imran

    I want to learn java programming

  16. florito

    its good to read this

  17. arunkumar

    confusing with lots of keywords, how to remember their usage..

  18. Tino nigeria

    I want to follow you along, pls show concern.

  19. srinidhi

    good work .than you

  20. srinidhi

    Good work .thank you

  21. Muskan Rathi

    Wat is d difference between class variable nd instance variable

  22. vinod

    it is really helpful for beginners to learn java basics..
    is it possible for you to give some more examples for related topics.. thank you.. 🙂

  23. Santos

    more clarification about java programing in 1.Local variable 2.Instance variable 3.Static variable
    and give the example by using demostration

  24. Ragaranjàni

    Very useful to me…

  25. suchitra

    Previously i was having difficulty with all these topic , but now i m confident with these topic.

    A lot of thanx to you….

  26. north africa

    good website for java, i will visit again

  27. camisetas futbol 2016

    This design is spectacular! You certainly know how to keep a reader entertained.

    Between your wit and your videos, I was almost moved to start my own blog (well, almost…HaHa!) Excellent job.
    I really enjoyed what you had to say, and more than that, how you presented it.

    Too cool!

  28. B Hari Pravin

    Good Explanation.

  29. Hasini

    Thankz.. it is easy to understand.

  30. Macmillian

    Is it possible to assign a value to an instance variable during declaration stage?

  31. SUMIT KUMAR GUPTA

    is global variable or instance variable same or not?

  32. Waqas Shah

    Hi,
    Thank you so much for making such a great website.

    It made me understand the static topic very clearly.

  33. asdf

    Why the ***** is this comment section so toxic and full of illegible broken english

  34. alia

    Really cool blog., you have done a well job on this topic.thanks. will read on

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