ArrayList One loop sorted, the other unsorted

Question

For this assignment I need to sort one list and also keep the original list, but when I click the button twice, the original list is also sorted.

        String output = "";
    String sortedOutput = "";

    //ORIGINAL OUTPUT
    for (int j = 0; j < song.size(); j++){
        output += song.get(j) + "\n";
    }

    //SORTED OUTPUT
    for (int k = 0; k < song.size(); k++){
        Collections.sort(song);
        sortedOutput += song.get(k) + "\n";

    }

    titleArtistOutput.setText("Original Order\n" + output + "\nSorted Order\n" + sortedOutput);

Is there anything I can put on the first loop to prevent it from getting sorted?

EDIT:

Thank you Jon Skeet!

I made another arraylist

String output = "";
String sortedOutput = "";

List <String> sortedSongs = new ArrayList <String> (song);

 for (int j = 0; j < song.size(); j++){
    output += song.get(j) + "\n";
}

for (int k = 0; k < song.size(); k++){
    Collections.sort(sortedSongs);
    sortedOutput += sortedSongs.get(k) + "\n";

}

titleArtistOutput.setText("Original Order\n" + output + "\nSorted Order\n" + sortedOutput);

Sorry for the easy question, I am new to programming.

Answer 1

I suspect you just want to take a copy of the list, then sort that:

List<Song> sortedSongs = new ArrayList<Song>(song);
Collections.sort(sortedSongs); // Will not affect song

Note that this should be done before your loop, not inside it.

Answer 2

Because when you are clicking the second time,the list is already sorted from the first time process. Do it like below, here I have took 'songDuplicate' list whose sorting doesn't affects the original list.

String output = "";
String sortedOutput = "";

//ORIGINAL OUTPUT
for (int j = 0; j < song.size(); j++){
    output += song.get(j) + "\n";
}
ArrayList<String> songDuplicate = new ArrayList<String>();
//SORTED OUTPUT
for (int k = 0; k < songDuplicate.size(); k++){
    Collections.sort(songDuplicate);
    sortedOutput += songDuplicate.get(k) + "\n";

}

titleArtistOutput.setText("Original Order\n" + output + "\nSorted Order\n" + sortedOutput);

Answer 3

You need to make copy of your original list. Maybe you can create copy when you create output from the original list.

    String output = "";
    String sortedOutput = "";
    List sorted = new ArrayList();

    //ORIGINAL OUTPUT
    for (int j = 0; j < song.size(); j++){
        output += song.get(j) + "\n";
        sorted.add(song.get(j));
    }

    Collections.sort(sorted);

    //SORTED OUTPUT
    for (int k = 0; k < sorted.size(); k++){
        sortedOutput += sorted.get(k) + "\n";

    }

    titleArtistOutput.setText("Original Order\n" + output + "\nSorted Order\n" + sortedOutput);

Answer 4

1. Use a debugger to understand each step of the computation.
2. You only have one list. Consequently, after you sorted it, it is sorted. Real.
3. RTFM: http://docs.oracle.com/javase/7/docs/api/java/util/Collections.html#sort%28java.util.List%29 Sort() does not return a sorted copy of the original list. It modifies it until it is sorted.