Code works, but won't pass one of the conditions

Question about the task

Five winners

Java Syntax, Level 8, Lesson 11

Under discussion

Anyone know why?

Create an array of 20 numbers.
Populate it with numbers from the keyboard.
Display the five largest numbers.
Each value should be on a new line.

Requirements:

The program should display numbers on the screen.
The program should read values from the keyboard.
The Solution class must have two methods.
The sort() method should sort the array of numbers from highest to lowest.
The main() method should call the sort() method.
The program should display the five largest numbers in the array. Each value should be on a new line.

package com.codegym.task.task08.task0826; import java.io.BufferedReader; import java.io.InputStreamReader; import java.util.Arrays; /* Five winners */ public class Solution { public static void main(String[] args) throws Exception { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); int[] array = new int[20]; for (int i = 0; i < array.length; i++) { array[i] = Integer.parseInt(reader.readLine()); } sort(array); System.out.println(array[0]); System.out.println(array[1]); System.out.println(array[2]); System.out.println(array[3]); System.out.println(array[4]); } public static void sort(int[] array) { int[] copy = array; Arrays.sort(copy); int j = copy.length - 1; for(int i = 0; i < array.length; i++){ array[i] = copy[j]; j--; } } }

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Alfred Walther

Level 24 , Frankfurt, Deutschland

13 August 2020, 13:12

You need a double loop like this:

for (int i = 0; i < array.length; i++) {
            for (int j = i + 1; j < array.length; j++) {
              ...
            }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

24 July 2020, 14:29

The sort method (line 29) will be incorrect because line 30 sets "copy" to the same object as "array". Think of this as like tying two handles (the variables) to the same exact balloon (the object). Between lines 31 and lines 32, directly after the code sorts "copy", if you output both "copy" and "array" you will see that they both have been sorted. Once again it is because both the variables are connected to the same object. So:

public static void sort(int[] array) {
   int[] copy = array;
   Arrays.sort(copy);
   // This sorts the one object and outputting "array" and "copy" which both point to that one object will result in the both
   // being the same
   System.out.println(Arrays.toString(array));
   System.out.println(Arrays.toString(copy));
   /* the rest of code */
}

Now this is a problem in that when you take the back number and put it at the front (as the loop at line 33 does) you effectively over-right the values at the front half of the object. It will end up duplicating all the values in the back half of the int[] object. So if I had an array with 5 numbers: [1, 2, 3, 4, 5] and this code ran: first loop cycle (i = 0, j = 4) 5 would be moved to the front and the result would be [5, 2, 3, 4, 5] second cycle (i = 1, j = 3) 4 would be moved to index 1. Result: [5, 4, 3, 4, 5] third loop cycle (i = 2, j = 2) 3 would be moved to its same location at index 2 Result: [5, 4, 3, 4, 5] At this point the numbers are just duplicates and no actual changes are made: (i = 3, j = 1) values at both indices are 4 (i = 4, j = 0) values at both indices are 5 So the sort method does not sort the array properly in reverse order and this is why the task is failing.