I have no idea what's wrong. Can U help me pls?

Question about the task

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I completed this task with a lot help from Agent Smith. Thank you very much!

1. In the Cat class, add the public static ArrayList<Cat> variable cats.
2. Each time a new cat (new Cat object) is created, add it to the variable cats. Create 10 Cat objects.
3. The printCats method should display all cats on the screen. You need to use the variable cats.

Requirements:

Add the public static ArrayList<Cat> variable cats to the Cat class.
The variable cats must be initialized.
The main method should create 10 Cat objects (use the Cat() constructor).
The main method must add all the created cats to the variable cats.
The printCats method should display all the cat objects in the variable cats. Each on a new line.

package com.codegym.task.task06.task0614; import java.util.ArrayList; /* Static cats */ public class Cat { public static ArrayList<Cat> cats = new ArrayList<Cat>(); public Cat() { cats.add(this); } public static void main(String[] args) { for(int i = 0; i < 10; i++) { Cat cat = new Cat(); cats.add(cat); } printCats(); } public static void printCats() { for(int j = 0; j < 10; j++) { System.out.println(cats.get(j)); } } }

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Agent Smith

Level 38

17 August 2020, 10:53

useful

Line 14: You don't need that instance variable. Lines 18-26: You can't have a for loop outside a method or constructor, it won't compile. You can add a Cat to an array of cats when a cat is created by using Cat constructor:

public Cat() {
    array.add(this);
}

It is better to use for-loop in your printCats() method, since it is repeating the same action:

for(Cat catReference : array) {
    System.out.println(catReference);
}

This is called an enchanced for-loop, very handy and easy to use. They introduce it in later lessons, but nothing can stop you from mastering it now. ;) The last thing you have to do is to populate your array with cats. You can do it inside main method with an ordinary for loop and this statement:

new Cat();

Karolina

Level 7 , Poland

17 August 2020, 13:23

Thank you very much, but I still can't understand the last point. Now I'm editing my question to show you what's still wrong. But thank you one more time :D.

Agent Smith

Level 38

17 August 2020, 14:03

useful

This code block should be inside main method:

for(i = 0; i < 10; i++)  {
    Cat cat = new Cat();
}

Study your program structure again carefully, it is very important to understand: Level 1 - You have a class Cat:

public class Cat {
    // body of class Cat
}

Level 2 - Inside your Cat class you have: 2.1 Cat class (static) variable array which is an array of Cat objects, where you store all created cat objects. 2.2 Cat() class constructor (which is automatically executed every time your create a Cat object using keyword new). 2.3 printCats() method, which prints cats array contents. 2.4 main() method, which is your program starting point. On line 17 you have a for loop that is outside any method/constructor, which is illegal. Class can't have "stuff" outside methods/constructors like that. The basic concept of a class is this: Class can have methods, constructors or variables. You store object state inside instance (non-static) variables, class state inside class (static) variables, and you manipulate class/object state via its methods. You can have another classes inside a class too, but that will be covered in later lessons so ignore this notion for now. Trying to solve this task step by step, you can use the following logic: 1) I need a class variable to store an array of cats, I should declare and initialize it. 2) I need to make my class constructor to add every new Cat object I create inside array of cats. 3) I need to write a method which'll display cat array contents. 4) Finally, when the program starts, I'll create 10 Cat objects with a for loop. Every time a cat object is created - it'll call its constructor which adds it to class array. 5) The cat array is now populated with cats, so it is time to call printCats() method.

Agent Smith

Level 38

17 August 2020, 17:08

You don't need line 32.

Karolina

Level 7 , Poland

18 August 2020, 08:56

Yes I know, I deleted it. You see line 32, because Codegym didn't want to upload new code (now it did it) . Now I added one line and now I have a problem with 5th requirement not 4th :).

Karolina

Level 7 , Poland

18 August 2020, 09:01

Ok, forget about it. I compleded it - I simply had to move one line of code to another place! Thank you very much for your time!