Are static methods always loaded into memory?

Question

Say that I have a Java project with some "Utils" classes, and that those classes have only static methods and members.

Once I run my application, are those methods and members automatically loaded into memory? Or that only happens once I call the class along the code?

EDIT: Some sample code to illustrate my question.

RandomUtils.java

public class RandomUtils {

    private static Random rand = new Random();

    public static int randInt(int min, int max) {
        // nextInt is normally exclusive of the top value,
        // so add 1 to make it inclusive
        return rand.nextInt((max - min) + 1) + min;
    }
}

MainClass.java

public class MainClass {
        public static void main(String[] args) {
            // Some other operations. Is my class already loaded here?

            int randomNumber = RandomUtils.randInt(1,10); // Or is it only loaded here?
        }
}

And what if that class have other static members and methods, and if it loads only once I call one of them, the other methods are loaded as well?

For a general discussion see: http://javarevisited.blogspot.com/2012/07/when-class-loading-initialization-java-example.html — mhp, Jan 11 '16 at 13:46

score 4 · Accepted Answer · answered Jan 11 '16 at 14:00

4

Static methods (and non-static methods, and static/member variables) are not loaded into memory directly: the declaring class is loaded into memory in its entirety, including all declared methods and fields. As such, there is no difference in the way that static/non-static methods/fields are loaded.

A class is only loaded by a class loader the first time it is referenced by other code. This forms the basis of the Initialization on demand idiom.

answered Jan 11 '16 at 14:00

Andy Turner

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So the only real difference is that I don't need to create an object for that, right? – Mauker Jan 11 '16 at 15:28
You don't need to create an *instance* of that class, no. – Andy Turner Jan 11 '16 at 15:29
I mean, both `static` and `non-static` will load the Class fully on the memory once called and instantiated, right? – Mauker Jan 11 '16 at 15:31
1

You can't load part of a class. You have to load the whole class to use any of it. – Andy Turner Jan 11 '16 at 16:09

score 2 · Answer 2 · answered Jan 11 '16 at 14:01

2

Your class is loaded when (among other conditions) its static method is called for the first time. See reference.

answered Jan 11 '16 at 14:01

dejvuth

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Mahesh Giri · Answer 3 · 2016-01-11T13:44:11.200

1

static methods loads only once when you call class.

college="ITS" is an static variable

edited Jan 11 '16 at 13:44

answered Jan 11 '16 at 13:43

Mahesh Giri

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college is an static variable that loads only once when you call the class – Mahesh Giri Jan 11 '16 at 13:45
How does it show that? What is `college` actually used for? Is there meant to be some code accompanying the diagram? – Andy Turner Jan 11 '16 at 13:46
s1 and s2 are class objects.Using this objects we can directly access value of college variable.This same happens with static methods. – Mahesh Giri Jan 11 '16 at 13:49

score 0 · Answer 4 · answered Jan 11 '16 at 13:52

0

it happens once you call the class.

answered Jan 11 '16 at 13:52

Mehdi TAZI

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Are static methods always loaded into memory?

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