What is an instance variable in Java

Question

My assignment is to make a program with an instance variable  a string  that should be input by the user  But I don t even know what an instance variable is  What is an instance variable  How do I create one  What does it do

User · Accepted Answer

Instance variable is the variable declared inside a class, but outside a method: something like:

class IronMan {

    /** These are all instance variables **/
    public String realName;
    public String[] superPowers;
    public int age;

    /** Getters and setters here **/
}

Now this IronMan Class can be instantiated in another class to use these variables. Something like:

class Avengers {

    public static void main(String[] a) {
        IronMan ironman = new IronMan();
        ironman.realName = "Tony Stark";
        // or
        ironman.setAge(30);
    }

}

This is how we use the instance variables. Shameless plug: This example was pulled from this free e-book here here.

User · Answer

An instance variable is a variable that is a member of an instance of a class  i e   associated with something created with a new   whereas a class variable is a member of the class itself  Every instance of a class will have its own copy of an instance variable  whereas there is only one of each static  or class  variable  associated with the class itself  What   s the difference between a class variable and an instance variable  This test class illustrates the difference  public class Test           public static String classVariable    quot I am associated with the class quot       public String instanceVariable    quot I am associated with the instance quot            public void setText String string           this instanceVariable   string                 public static void setClassText String string           classVariable   string                 public static void main String   args            Test test1   new Test            Test test2   new Test                        Change test1 s instance variable         test1 setText  quot Changed quot            System out println test1 instanceVariable      Prints  quot Changed quot             test2 is unaffected         System out println test2 instanceVariable      Prints  quot I am associated with the instance quot                      Change class variable  associated with the class itself          Test setClassText  quot Changed class text quot            System out println Test classVariable      Prints  quot Changed class text quot                      Can access static fields through an instance  but there still is only one             not best practice to access static variables through instance          System out println test1 classVariable      Prints  quot Changed class text quot          System out println test2 classVariable      Prints  quot Changed class text quot

[java] What is an instance variable in Java?

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