remove cat1 in set cats

Question about the task

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Hi, 1) I don't understand why cat1 in line 19 can't be resolved to a variable (the message I get from my IDE). 2) Is there another way to remove a specific cat from the set, without using a field of name? Why can't I just use the object reference? 3) I also tried in line 20: iterator.remove(cat1) - but doesn't work either.. Anyone, who can explain and help? Thank you! :)

1. Inside the Solution class, create a public static Cat class.
2. Implement the createCats method. It must create a Set of cats and add 3 cats to it.
3. In the main method, remove one cat from Set cats.
4. Implement the printCats method. It should display all the cats that remain in the set.
Each cat on a new line.

Requirements:

The program should display text on the screen.
Inside the Solution class, there must be a public static Cat class with a default constructor.
The Solution class's createCats() method must return a Set containing 3 cats.
The Solution class's printCats() method must display all the cats in the set. Each cat on a new line.
The main() method should call the createCats() method once.
The main() method should call the printCats() method.
The main() method must remove one cat from the set of cats.

package com.codegym.task.task08.task0819; import java.util.HashSet; import java.util.Iterator; import java.util.Set; /* Set of cats */ public class Solution { public static void main(String[] args) { Set<Cat> cats = createCats(); Iterator<Cat> iterator = cats.iterator(); while (iterator.hasNext()) { Cat cat = iterator.next(); if (cat.equals(cat1)) { iterator.remove(); } } printCats(cats); } public static Set<Cat> createCats() { Cat cat1 = new Cat(); Cat cat2 = new Cat(); Cat cat3 = new Cat(); Set<Cat> cats = new HashSet<>(); cats.add(cat1); cats.add(cat2); cats.add(cat3); return cats; } public static void printCats(Set<Cat> cats) { for (Cat cat : cats) { System.out.println(cat); } } public static class Cat { } }

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Guanting Liu

Level 16 , Springfield, United States

23 December 2020, 06:26

U problem is u try to remove a cat1 which it's not initialized in your main method. And the problem is very simple,remove one cat, because set doesn't have a remove(index) method, it's pretty hard to remove which object u want in an iterator if u want to use index. But u know what u have in set,which is cat1,cat2,cat3. U want to remove one,it could be a simple line code:cat.remove(cat1) without using iteratora and worrying about some other problems which could be really difficult in data structure but u don't need to worry about them here.

Guadalupe Gagnon

Level 37 , Tampa, United States

21 December 2020, 19:13

Line 19 is using is using a variable, cat1, that doesn't exist in that block of code. There would need to be a variable named cat1 declared in one of the blocks of codes that surrounds that line for it to be used. They are: The Solution class block of code from lines 1-50 The main block of code from lines 13-26 The while loop block of code from lines 17-23 There is a variable cat1 declared on line 29, but because this is not in a block of code that surrounds line 19, it can't be referenced from there. So, some simple examples:

{
   {
       Cat cat1 = new Cat();
   }
   cat1.doSomething();
}

Here cat1 is declared in an inner block of code. It will go out of scope when that block ends and the doSomething() method is illegal because cat1 doesn' exist in the outer block of code

{
   Cat cat1 = new Cat();
   {
       cat1.doSomething();
   }
}

Here cat1 is declared in the outer block of code. Now any code blocks surrounded by the outer block have access to that variable (in scope). This is acceptable code. There is a benefit to this, you can use duplicate variable names in multiple locations in your code as long as the name does already exist in the direct surrounding blocks:

{
   for(int i = 0; i < 10; i++) { }
   for(int i = 0; i < 10; i++) { }
   for(int i = 0; i < 10; i++) { }
   for(int i = 0; i < 10; i++) { }
}

Here, even though the variable i is declared in 4 spots, they are all part of their own for loop block of code and there is not problem.

for(int i = 0; i < 10; i++){
   for(int i = 0; i < 10; i++) {}
}

Here the second for loop is within the first making the variable i exist in 2 spots in the same block of code. This would be an error and not compile.

Anitamalina

Level 18 , København, Denmark

22 December 2020, 01:43

okay, thank you. So, line 19 would be: if (cat.equals(cat)). But how can I control which cat from the HashSet I want to remove? fx. "cat1" that exist in the hashSet already?

Guadalupe Gagnon

Level 37 , Tampa, United States

22 December 2020, 02:55

You would need to write code to identify which cat you want to remove, which is above the scope of this task. It says to remove one Cat object from the set, which you can do by simply just removing any one Cat object. Whichever method you arrive at to remove one, and only one, cat will be correct.