Error on Condition 3 (using the constructor)

Question about the task

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My code now prints the values of the objects, but I'm getting another error. If I un-comment line 15, it verifies that the constructor is being run 10 times. My output is: 0 5 10 15 20 25 30 35 40 45 So I have 10 objects in the arrayList. I don't understand how I am not meeting condition 3.

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 { //write your code here int x; public static ArrayList<Cat> cats = new ArrayList<Cat>(); public Cat(int x) { //System.out.print("Constructor: x=" + x + " "); // verify that the constructor is being run this.x = x; } @Override public String toString() { // print the value of the object return Integer.toString(x); } public static void main(String[] args) { //write your code here for(int i = 0; i<10; i++) { Cat cat = new Cat(i*5); //System.out.println("cat(" + i + ")=" + cat.x); //Cat.cats.add(new Cat(i)); Cat.cats.add(cat); } //System.out.println(Cat.cats.size()); printCats(); } public static void printCats() { //write your code here for(int i = 0; i<cats.size(); i++) { //for(Cat cat: cats) { System.out.println(cats.get(i)); } } }

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Nithin

Level 35 , Hyderabad, India

24 July 2019, 01:21

I think you should use only empty constructor. Remove the variable x

John

Level 8 , United States

24 July 2019, 18:51

Why? The constructor runs either way, so what is the difference?

Nithin

Level 35 , Hyderabad, India

25 July 2019, 01:43

You need to follow their requirements if you want to pass the validation. in 3rd requirement they said "use the Cat() constructor". So try using empty constructor

Monica Nicoleta

Level 7 , Arad, Romania

26 July 2019, 08:37

As I see it, the constructor must be empty because we are dealing with static methods here, where <this> equals null. We are only supposed to create the Cat objects and add them to the array list, so there will be no references to them. And we only need to create one object and add it to the list because the for loop will do the rest (for example: Cat cat1 = new Cat(); cats.add(cat1)) For the printCats() method you should cancel line 39 and uncomment line 40. If you do that, you only need to print <cats>. Also, I dont think the override and the toString() method are necessary here, neither int x

John

Level 8 , United States

29 July 2019, 02:52

This still doesn't make sense to me. Even objects with 'null' values have references (that's what get printed out). I guess since the condition says to call the Cat() constructor, you have to do it with the default constructor. That seems pretty picky to me.

Monica Nicoleta

Level 7 , Arad, Romania

1 August 2019, 16:58

I guess the idea of the task is to simply create the 10 cat objects, so that they can be added to the variable cats. But for this to happen, the variable cats must be initialized, and that's where the default constructor comes in.