when to use "this" and when to use Cat.

Question about the task

Cat and statics

Java Syntax, Level 6, Lesson 11

Under discussion

When should I use this and when to use Cat. to call the variable in Cat class?

public class Solution {
    public static void main(String[] args) {
        // Create 10 cats
        Cat cat1 = new Cat();
        Cat cat2 = new Cat();
        Cat cat3 = new Cat();
        Cat cat4 = new Cat();
        Cat cat5 = new Cat();
        Cat cat6 = new Cat();
        Cat cat7 = new Cat();
        Cat cat8 = new Cat();
        Cat cat9 = new Cat();
        Cat cat10 = new Cat();
        // Display the value of the variable catCount
        System.out.print(Cat.catCount);
    }

    public static class Cat {
        // Create a static variable catCount
        static public int catCount=0;

        // Declare a constructor
        public Cat(){
            catCount++;
        }
    }
}

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Gellert Varga

Level 23 , Szekesfehervar, Hungary

9 January 2021, 22:21

useful

A little clarifying: Static or non-static - what exactly do they mean? For example:

public class Cat {
     int age;
     String name;
     static int count;
. . .

1) "static". (variable 'count'). (Other name: class-variable, class-method.) This means: this static variable (or a static method) belongs only to its own class. It doesn't belong to any object. You can create objects from the class Cat, but the static 'count' variable will be not the part of any Cat type object! This is the way to do something with a static variable. If you are inside an other class, write this for example: Cat.count = Cat.count + 1; If you are inside the Cat class, you can write this: count = count + 1; 2) "non-static": (age, name): these variables belongs only to the created Cat-objects. Other name: instance-variable, instance-method. (instance means object!) If you don't create any Cat-object, then these variables don't even exist! If doesn't exist any Cat-object, then you can't use these instance variables. (The same applies to non-static methods too.) No one can do anything with these variables (methods), only the created objects can do something with them! The nonstatic variables and methods are just a pattern for future objects. If a Cat type object exists already, you can do something with it for example this way: cat1.age = 5; But if you are inside a non-static (instance) method of the Cat class, then you can write the followings: this.age = ... or this.name = ... etc. The "this.age" means the "age" variable of that Cat-object which one was called to this non-static method.

J H U X

Level 7 , Alkmaar, Netherlands

25 January 2021, 09:39

Thank you for this explanation. It makes it so much easier to understand now.

Gellert Varga

Level 23 , Szekesfehervar, Hungary

25 January 2021, 20:37

Cheers!:)