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This is a Java implementation of Bubble sort algorithm, I have used another class with a swap method and this code works fine when I don't use a constructor in my swapper class but does not swap the array at all if a constructor is present.

import java.io.*;
import java.math.*;
import java.text.*;
import java.util.*;
import java.util.regex.*;

class swapper {
  int x, y;

  void swap() {
    int temp = x;
    x = y;
    y = temp;
  }
}

public class Solution {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int n = in.nextInt();
    int[] a = new int[n];
    for (int a_i = 0; a_i < n; a_i++) {
      a[a_i] = in.nextInt();
    }
    int swaps = 0;
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < n - i - 1; j++) {
        if (a[j] > a[j + 1]) {
          swaps++;
          swapper s = new swapper();
          s.x = a[j];
          s.y = a[j + 1];
          a[j] = s.y;
          a[j + 1] = s.x;
        }
      }
    }
    System.out.println(
        "Array is sorted in "
            + swaps
            + " swaps.\nFirst Element: "
            + a[0]
            + "\nLast Element: "
            + a[n - 1]);
  }
}

But when I use a constructor to assign values of x and y of my 's' Object, this code does not swap any element at all. 

import java.io.*;
import java.math.*;
import java.text.*;
import java.util.*;
import java.util.regex.*;

class swapper {
  int x, y;

  swapper(int a, int b) {
    x = a;
    y = b;
  }

  void swap() {
    int temp = x;
    x = y;
    y = temp;
  }
}

public class Solution {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int n = in.nextInt();
    int[] a = new int[n];
    for (int a_i = 0; a_i < n; a_i++) {
      a[a_i] = in.nextInt();
    }
    int swaps = 0;
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < n - i - 1; j++) {
        if (a[j] > a[j + 1]) {
          swaps++;
          swapper s = new swapper(a[j], a[j + 1]);
          s.swap();
          a[j] = s.y;
          a[j + 1] = s.x;
        }
      }
    }
    System.out.println(
        "Array is sorted in "
            + swaps
            + " swaps.\nFirst Element: "
            + a[0]
            + "\nLast Element: "
            + a[n - 1]);
  }
}

The only difference in both the codes is the presence of a constructor to assign values to the instance variables.

The first code has manual assignments of values whereas the second code uses a constructor.

Manav
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    Too much code, that too not formatted. Please provide [Minimal, Complete, and Verifiable example](https://stackoverflow.com/help/mcve) – vinS Dec 12 '17 at 12:13
  • I have looked up referencing in Java and can't figure out anything, any help is appreciated. – Manav Dec 12 '17 at 12:13
  • just don't call the `swap` method, like you did not in the first code... or do not swap the assignment. – user85421 Dec 12 '17 at 12:23

1 Answers1

2

You are essentially swapping the two numbers twice, and therefore not swapping them at all:

swapper s = new swapper(a[j],a[j+1]); // this assigns a[j] to s.x and a[j+1] to s.y
s.swap(); // this swaps s.x and s.y
a[j] = s.y; // this assigns the original value of s.x (a[j]) to a[j]
a[j+1] = s.x; // this assigns the original value of s.y (a[j+1]) to a[j+1]

In order for the swapping to work as expected, change it to:

swapper s = new swapper(a[j],a[j+1]); 
s.swap();
a[j] = s.x;
a[j+1] = s.y;
Eran
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