How does this array length work?

[soft wave]

Somehow this code shows the following output: "The number of topics is 4". I am mainly confused with this code:

    
    System.out.println("The number of topics is "+ sampleFeed.getNumTopics());```

How is it able to know the length is 4?

```import java.util.Arrays;

public class Newsfeed {
  
  String[] topics = {"Opinion", "Tech", "Science", "Health"};
  int[] views = {0, 0, 0, 0};
  
  public Newsfeed(){

  }
    
  public String[] getTopics(){
    return topics;
  }
  
  public int getNumTopics(){
    return topics.length;
    
  }
  
  public static void main(String[] args){
    Newsfeed sampleFeed = new Newsfeed();
    
    System.out.println("The number of topics is "+ sampleFeed.getNumTopics());
   
  }
}

[rich wharf]

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[forest musk]

Well the method in question just returns the length of the array that holds the topics

[soft wave]

Yeah I think I see it now, the Newsfeed sampleFeed = new Newsfeed(); confused me, what is that doing exactly?

first it runs this in main()

[forest musk]

Well you create a new instance of the class Newsfeed

an object

[soft wave]

we need to do that?

[forest musk]

well you might want to have more than one Newsfeed in your program

[soft wave]

but for this output, not theoretically

is this Newsfeed sampleFeed = new Newsfeed(); required to achieve this output: "The number of topics is 4"

[forest musk]

If everything were static/ wouldn't run on the basis of objects we couldn't have different data

[forest musk]

since getNumTopics()isn't a static method yes

you would need an instance of the class from which you could call that method

[soft wave]

oh I see

if getNumTopics was static we could just use this for the method call?
Newsfeed.getNumTopics()?

[forest musk]

yeah

[soft wave]

and it would work just the same?

[forest musk]

no

[soft wave]

I mean, the output would be the same

[forest musk]

because the method uses instance variables

it wouldn't work

[soft wave]

it wouldn't show an output at all if we did this?

syntax error?

[rich wharf]

https://tryitands.ee/

[soft wave]

someone bought this domain for JavaBot?

I wonder if they live in Estonia for the .ee TLD

[forest musk]

Someone surely did. But not us no.

JavaBot is a creation of this discord.

[soft wave]

Made in Java?

[forest musk]

https://github.com/Java-Discord

[soft wave]

so I tested in Eclipse IDEA and if I use static I also have to make the array static too

static String[] topics = {"Opinion", "Tech", "Science", "Health"};

[forest musk]

yeah 🙂

[soft wave]

this way I can remove the object, HelloWorld sampleFeed = new HelloWorld();

and call it like this: System.out.println("The number of topics is "+ HelloWorld.getNumTopics());

[forest musk]

makes 0 sense but sure

[soft wave]

wdym?

[forest musk]

well why would you get rid of the functionality? why would you want HelloWorldto be a completely static class?

[soft wave]

I'm not sure

I was wondering that myself

why would anyone wanna use static based?

if instance based is better

[forest musk]

its different not better

sometimes I would want a static method 🙂

[soft wave]

oh yeah, I changed the class name because I tested in an existing HelloWorld.java file

[soft wave]

can you give an example where static is more effective than instance based?

maybe not "better" per say

because I honestly don't know when to use instance or class based

main() appears to be class based, this is so that JVM runs it like this: ClassName.main() without instantiating a new object

so in terms of main() it must be static, otherwise JVM fails

[forest musk]

in 90% of the cases you would use an instance based approach

[soft wave]

Hmmm, OK

[forest musk]

here is a SO post that is quite good

https://stackoverflow.com/questions/2671496/when-to-use-static-methods

[soft wave]

btw, is it JVM or JRE?

probably not too important, but just curious

[forest musk]

especially the second answer is for u I guess

[soft wave]

ty

OK so depends on the field

it can be combination of instance and static based, I believe

depends on the fields and what works best for them

in the case of main() it works best with class based

maybe it's less memory usage, no new object is required, not sure

or just easier to use in that case, otherwise we would be doing this every time which is even more code:
"ClassName main = new ClassName()"