Instance Variable in Java

An Instance variable in Java is used by Objects to store their states. Variables that 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.

If a class has an instance variable, then a new instance variable is created and initialized to a default value as part of the object creation of the class or subclass.

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 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. Meaning STATIC is one of the keyword which cannot be used with Instance variable.
  • The instance variable will get a default value, which means the 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 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;
  /*
   * 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;

  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);
  }

  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);
  }
}

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

References

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63 Comments

  1. Thanks for the info, it really means a lot to me, keep up the good work again, & looking for more in the future post of yours.

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

    It made me understand the static topic very clearly.

    • Yes. It is possible and completely valid.
      class superEmployee { public String lastName = "assigned Value"; }

  10. 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!

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

    A lot of thanx to you….

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

  15. 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.. 🙂

  27. 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.

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

  30. @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. 🙂

  31. Hi Bharat,

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

    • 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’

  32. 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);

    • Hi Bharat,

      You said you want to learn Java. As you can see there are articles i have written on site which would be helpful for you.

      Or if you want to direct learn Java by us do let me know. We are going to start online classes. Where you can start by enrolling, It will be paid classes.

      Thanks

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