Why don't we make everything static?

Question

Why can't we just make all methods and variables static, to save ourselves from the hassle of making objects?

I have actually had this question ever since I started learning Java a long time ago, but never asked it. I know that if a method or variable is not static, you can call it using an object you create:

public class classwithmethodandvariable {

    int i = 7;

    public void hello() {
    }

}

You can call this like so:

public class myMainClass {

    classwithmethodandvariable obj = new classwithmethodandvariable();
    classwithmethodandvariable.i++;  // ACCESS INT I AND INCREMENT
    classwithmethodandvariable.hello();  // CALLS METHOD HELLO

}

But, if we had made the method hello() and variable i we could have done everything with less lines of code, right?

public class classwithmethodandvariable {

    static int i = 7;

    public static void hello() {
    } 

}

You can call this like so:

public class myMainClass {

    classwithmethodandvariable.i++;  // ACCESS INT I AND INCREMENT
    classwithmethodandvariable.hello();  // CALLS METHOD HELLO

}

Why don't we do that? I have seen another question like this, but the answer says “Because you can't access instance variables from static methods”. But then what if you make the variables also static?

Answer 1

Object oriented programming is designed to hide state in an object and then provide a method (aka behavior) that modifies the state.

This is a very simple idea, but when combined with inheritance, interfaces, and other common design patterns allows for a very maintainable system.

The use of only static methods would prevent many of these design patterns from working, and so you would sacrifice maintainability, and extensibility of your system.

Answer 2

Why can't we just make all methods and variables static, to save ourselves from the hassle of making objects?

You can. If you really wanted to, there is nothing stopping you^{1, 2}.

However, that is not how Java was designed to be used. And you will find that your code base get increasingly hard to test and maintain as it gets larger (compared to OO code). And you will also find that other Java developers are liable to run away screaming if they are asked to read your code.

If you really cannot get your head around OO, and/or you cannot accept that OO's benefits out-weigh the "hassle of making objects", then you would be better off using another language. Pick one that is non-OO (like C, old-school BASIC) or that is more conducive to non-OO programming (C++ used like C, Python, Perl, etc.)

---

^{1 - "Besides, a determined Real Programmer can write FORTRAN in any language." is one of the best lines in "Real Programmers don't use Pascal."}

^{2 - Actually, some Java APIs can only be used effectively if you create and use custom classes.}

Answer 3

Think of a cookie (the kind you bake) as an object. Now think of a cookie cutter as a class. Just as the cookie cutter is used to makes cookies, classes are used to make objects (via instantiation, typically by an operator named new). An object is an "instance of a class." Objects are NOT classes. Don't confuse the two. Objects are instances of classes. Buildings are instances of blue prints, cookies are instances of cookie cutters. A class is a set of "instructions" for making objects. You can add your own information to a class by using statics. Just like the instructions for making objects, there is only one of every static in a class. If you only need one instance of a class, you can make all the variables static (this works, but it's not advised -- there are better ways). If you need multiple instances of a class, like a collection of identical objects (a basket of kittens) or related objects (a basket of mammals, which includes kittens and puppies), then, in general, you don't want to define variables as static (for example, each animal has its own birth date, name, description, weight, etc.). Anything you define as static exists only once and is common to all of the instantiated classes. If any one instance of the class changes the static value, all instances of the class see that change.

I suggest you read a good book about object oriented programming. Here's a good one:

Object Oriented Modeling and Design by James Rumbaugh, Michael Blaha, William Premerlani, Frecerick Eddy and William Lorensen).