Can't pass second check and a bug?

Question about the task

Resolved

The program seems to work. It will replace duplicates with null. Unless it refers to itself, then it continues. If I use Scanner.nextLine, it will end and display my results once I enter the 4th word, "Java". The only way I can enter more words is if I put something below it like a System.out.println(). Why is this? If I use Scanner.next() it works perfectly, but the checker won't take that. Seems like a bug.

In this task, you need to:

Read 6 strings and fill the strings array with them.
Remove duplicate strings from the strings array, replacing them with null (null, not the string "null").

Examples:
The array after reading the strings:
{"Hello", "Hello", "World", "Java", "Tasks", "World"}

The array after removing duplicate strings:
{null, null, null, "Java", "Tasks", null}

Requirements:

In the main(String[]) method, read 6 strings from the keyboard and fill the strings array with them.
In the main(String[]) method, remove (meaning, overwrite with null) any duplicated elements in the strings array.

package en.codegym.task.pro.task05.task0508; import java.util.Scanner; /* Remove duplicate strings */ public class Solution { public static String[] strings; public static void main(String[] args) { Scanner scanner = new Scanner(System.in); strings = new String[6]; for (int i = 0; i < strings.length; i++) { strings[i] = scanner.nextLine(); System.out.println(); } for (int i = 0; i < 6; i++) { for (int j = 1; j < strings.length; j++) { if (strings[i] == null) { continue; } if (strings[i] == strings[j]){ continue; } if (strings[i].equals(strings[j])) { strings[i] = null; strings[j] = null; } } } for (int i = 0; i < strings.length; i++) { System.out.print(strings[i] + ", "); } } }

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Jaime Padilla

Level 20 , Chandler, United States

9 June 2022, 17:37

In line 26 I meant to compare the reference values or address to see if they were the same. If they were the same, it would skip and move to the next. If they were not, it would continue to the next check which would check the value. I'm still learning, is my thought process correct? Does the == sign check the reference/address? While the equals.() checks the value? Strings are objects so when the scanner built each one they would have a different address? Also, I tested your built array and when built like this the words do seem to share the same address when checked by == so my reference check doesn't work. Do you have any articles that I could read to better understand this?

Guadalupe Gagnon

Level 37 , Tampa, United States

9 June 2022, 18:06

useful

The == sign will test reference when applied to objects. However, in this code and as Lisa said, it would run smoother to simply test if the indices were the same (i == j) instead of checking if the references were the same. Alternatively, because the j loop is inside the i loop, you can just start j at i + 1 and not even have to make that check: for(i loop starts at 0) { for(j loop starts at i +1) { } } This is sound logically and you don't need to worry about if the i index and j index are the same. You would still want to continue if the value at i is null already.

Guadalupe Gagnon

Level 37 , Tampa, United States

9 June 2022, 18:11

also, I am not sure about this since I don't have access to the "pro" tasks, but wouldn't removing duplicates mean remove any value that is in the list more than once. For example: {"Hello", "Hello", "Hello", "Java", "Tasks", "World"} Should that not end up being: {null, null, null, "Java", "Tasks", "World"}?

Jaime Padilla

Level 20 , Chandler, United States

9 June 2022, 19:11

Such great ideas, thank you. I don't know why I didn't just have it check the indices or even better the i = i + 1. Those work great, but for some reason my code still won't pass the checker.

package en.codegym.task.pro.task05.task0508;

import java.util.Scanner;

/*
Remove duplicate strings
*/

public class Solution {
    public static String[] strings;

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        strings = new String[6];
        for (int i = 0; i < strings.length; i++) {
            strings[i] = scanner.nextLine();
        }

        for (int i = 0; i < 6; i++) {
            for (int j = i + 1; j < strings.length; j++) {
                if (strings[i] == null) {
                    continue;
                }
                if (strings[i].equals(strings[j])) {
                        strings[i] = null;
                        strings[j] = null;
                }
            }
        }
        for (int i = 0; i < strings.length; i++) {
            System.out.print(strings[i] + ", ");
        }
    }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

9 June 2022, 20:03

Have you tried with my example? {"Hello", "Hello", "Hello", "Java", "Tasks", "World"} where it should remove the 3 "Hello" strings. last tip: Check if i equals null outside the j loop. If it is you want to increase i, not increase j:

for (int i = 0; i < 6; i++) {
   if (strings[i] == null)  // put his here
      continue;

Jaime Padilla

Level 20 , Chandler, United States

9 June 2022, 20:20

Hmm, you're right. It doesn't remove the 3rd Hello. I tried the if statement above for j loop and it spits on an error about null object

Jaime Padilla

Level 20 , Chandler, United States

9 June 2022, 20:29

The three Hello's helped me solve it. Thank you. I had to create a variable and continue checking that word while making null any that matched the variable.

Lisa L

Level 47 , Nuremberg, Germany

8 June 2022, 05:21

useful

This strange behavior disappeared when I updated IntelliJ (eventually make IntelliJ search for new updates) in line 26 you eventually meant to compare the index, not the value? This will make the code work when you use Scanner but will make the code fail when filling the array in another way (like the validation probably will do). just use this instead of your input loop to test that behavior

strings = new String[]{"1", "1", "2", "3", "4", "4"};