What is an instance variable in Java?

java instance-variables
aqua picture aqua · May 22, 2013 · Viewed 173.3k times · Source

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?

Answer

Yash Sharma picture Yash Sharma · May 22, 2013

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.

Related questions

How do servlets work? Instantiation, sessions, shared variables and multithreading

Suppose, I have a webserver which holds numerous servlets. For information passing among those servlets I am setting session and instance variables. Now, if 2 or more users send request to this server then what happens to the session variables? Will …

Read More
Should I instantiate instance variables on declaration or in the constructor?

Is there any advantage for either approach? Example 1: class A { B b = new B(); } Example 2: class A { B b; A() { b = new B(); } }

Read More
Static vs Instance Variables: Difference?

What is the difference between a static and instance variable. The following sentence is what I cant get: In certain cases, only one copy of a particular variable should be shared by all objects of a class- here a static …

Read More