Java Bubble-Sort Not checking the last loop through

November 24, 2021

I am trying to sort an ArrayList but hit a wall at the moment. Below, I have a getId() function that retrieves the id of a member. I want to sort the ArrayList by member id. I have checked a afew good articles on this and implemented the following :

e.g (before sort)
11
22
33
44
55
66
77
88
99
00

e.g (after sort)
00
11
22
33
44
55
66
77
88
99

Member temp;

for (int i = 0; i < members.size(); i++) {
    Member s = members.get(i);
    System.out.println("S: "+s.getId());
            
    for (int j=0; j < members.size()-1; j++) {
        Member t = members.get(j+1);
        System.out.println("T: "+t.getId());
                
        if (s.getId() > t.getId()) {
        temp = s;
        s = t;
        t = temp;
        }
     }
  }
}

I did the printout statements above to trace the root cause but still trying to figure out the error.

>Solution :

The code for swapping is wrong:

if (s.getId() > t.getId()) {
   temp = s;
   s = t;
   t = temp;
}

Here you only swap s with t, but the data underlying members are not affected. The correct one:

for (int i = 0; i < members.size() - 1; i++) {
     for (int j = 0; j < members.size() - i - 1; j++) {
         Member s = members.get(j);
         Member t = members.get(j+1);
         if (s.getId() > t.getId()) {
             Collections.swap(members, j, j+1);
         }
    }
}