通过对象字段过滤/排序集合？

Question

I'm not sure why this isn't working. I'm not sure if it's a problem with the printing, or if it's a problem with the methods themselves. I am making a program that takes a collection of songs and filters or sorts it according to a given user input. The user should be able to input multiple commands to further narrow down the list.

My filterRank and filterYear methods work perfectly fine, but the other methods end up printing a seemingly random selection of songs that do not change regardless of what is inputted as the title or artist to be filtered by, which generally appears only after an extremely long waiting period and a long series of spaces.

Even after this amalgam of songs is printed, the program does not terminate, and periodically outputs a space in the console, as in a System.out.println() statement were being continuously run.

If I remove the code that configures the output file, which is a requirement for the project, the methods fail to print entirely. Regardless of either of these changes, filterRank and filterYear continue to work perfectly.

This problem also occurs with my sort methods. No matter what sort method I run, it still prints out the spaces and the random songs, or nothing at all.

Is there something I'm missing? I've tried printing out variables and strategically inserting System.out.println("test") in my program to determine what the program is, but it seems as though it's parsing the input correctly, and the methods are indeed being successfully run. I've been otherwise unable to isolate the problem.

Can I get assistance in determining what I'm missing? Despite poring over my code for two hours, I just can't figure out what the logical error on my part is.

Here is the relevant code:

The main class:

public static void main(String[] args) throws FileNotFoundException, IOException{

//user greeting statements and instructions
//scanning file, ArrayList declaration


    Scanner input = new Scanner(System.in);

    while (input.hasNextLine()) {
        int n = 0;
        SongCollection collection = new SongCollection(songs);
        String inputType = input.nextLine();
        String delims = "[ ]";
        String[] tokens = inputType.split(delims);
        for (int i = 0; i < tokens.length; i++) {
            n = 0;
            if (n == 0) {
                if ((tokens[i]).contains("year:")) {
                    collection.filterYear(Range.parse(tokens[i]));
                    n = 1;
                }// end of year loop
                if ((tokens[i]).contains("rank:")) {
                    collection.filterRank(Range.parse(tokens[i]));
                    n = 1;
                }// end of rank
                if ((tokens[i]).contains("artist:")) {
                    collection.filterArtist(tokens[i]);
                    n = 1;
                }// end of artist
                if ((tokens[i]).contains("title:")) {
                    collection.filterTitle(tokens[i]);
                    n = 1;
                }// end of title
                if ((tokens[i]).contains("sort:")) {
                        if ((tokens[i]).contains("title")) {
                            collection.sortTitle();
                            n = 1;
                        }// end of sort title
                        if ((tokens[i]).contains("artist")) {
                            collection.sortArtist();
                            n = 1;
                        }// end of sort artist
                        if ((tokens[i]).contains("rank")) {
                            collection.sortRank();
                            n = 1;
                        }// end of sort rank
                        if ((tokens[i]).contains("year")) {
                            collection.sortYear();
                            n = 1;
                        }// end of sort year
                }//end of sort
            }// end of for loop

        }// end of input.hasNextline loop
        /*final PrintStream console = System.out; //saves original System.out
        File outputFile = new File("output.txt"); //output file
        PrintStream out = new PrintStream(new FileOutputStream(outputFile)); //new FileOutputStream
        System.setOut(out); //changes where data will be printed
           */           System.out.println(collection.toString()); 

        /*System.setOut(console); //changes output to print back to console
        Scanner outputFileScanner = new Scanner(outputFile); //inputs data from file
        while ((outputFileScanner.hasNextLine())) { //while the file still has data
            System.out.println(outputFileScanner.nextLine()); //print
        }
        outputFileScanner.close();
        out.close();*/
    }
}// end of main
}// end of class

The SongCollection Class, with all of its respective filter and sort methods:

  import java.io.File;
   import java.io.FileNotFoundException;
   import java.util.*;


    public class SongCollection {
ArrayList<Song> songs2;
ArrayList<Song> itemsToRemove = new ArrayList<Song>(); // second collection
                                                        // for items to
                                                        // remove
public SongCollection(ArrayList<Song> songs) { // constructor for SongCollection
    System.out.println("Test"); 
    this.songs2 = songs;
    }
public void filterYear(Range r) {
    int n = 0;
    if (n == 0) {
        System.out.println("Program is processing.");
        n++;
        for (Song song1 : songs2) {
            if (song1.year > (r.getMax()) || (song1.year) < (r.getMin())) {
                itemsToRemove.add(song1);
            }
        }
        songs2.removeAll(itemsToRemove);
        itemsToRemove.clear();
    }
}

public void filterRank(Range r) {
    int n = 0;
    if (n == 0) {
        System.out.println("Program is processing.");
        n++;
        for (Song song1 : songs2) {
            if (song1.rank > (r.getMax()) || (song1.rank) < (r.getMin())) {
                itemsToRemove.add(song1);
            }
        }
        songs2.removeAll(itemsToRemove);
        itemsToRemove.clear();
    }
}

public void filterArtist(String s) {
    int n = 0;
    if (n == 0) {
        System.out.println("Program is processing.");
        n++;
        for (Song song1 : songs2) {
            if ((!(((song1.artist).contains(s))))) {
                itemsToRemove.add(song1);
            }
        }
        songs2.removeAll(itemsToRemove);
        itemsToRemove.clear();
    }
}

public void filterTitle(String s) {
    int n = 0;
    if (n == 0) {
        System.out.println("Program is processing.");
        n++;
        for (Song song1 : songs2) {
            if ((!(((song1.title).contains(s))))) {
            itemsToRemove.add(song1);
            }
        }
        songs2.removeAll(itemsToRemove);
        itemsToRemove.clear();
    }
}

public void sortTitle() {
      Collections.sort(songs2, SongComparator.byTitle()); // now we have a sorted list
    }
public void sortRank() {
      Collections.sort(songs2, SongComparator.byRank()); // now we have a sorted list
    }
public void sortArtist() {
      Collections.sort(songs2, SongComparator.byArtist()); // now we have a sorted list
    }
public void sortYear() {
      Collections.sort(songs2, SongComparator.byYear()); // now we have a sorted list
    }
public String toString() {
    String result = "";
    for (int i = 0; i < songs2.size(); i++) {
        result += " " + songs2.get(i);
    }

    return result;

}
}

SongComparator Class:

import java.util.Comparator;

public class SongComparator implements Comparator<Song> {
public enum Order{
    YEAR_SORT, RANK_SORT, ARTIST_SORT, TITLE_SORT
}
private Order sortingBy;
public SongComparator(Order sortingBy){
    this.sortingBy = sortingBy;
}
public static SongComparator byTitle() {
    return new SongComparator(SongComparator.Order.TITLE_SORT);
}
public static SongComparator byYear() {
    return new SongComparator(SongComparator.Order.YEAR_SORT);
}
public static SongComparator byArtist() {
    return new SongComparator(SongComparator.Order.ARTIST_SORT);
}
public static SongComparator byRank() {
    return new SongComparator(SongComparator.Order.RANK_SORT);
}

@Override
public int compare(Song song1, Song song2) {
    switch (sortingBy) {
    case YEAR_SORT:
        System.out.println("test");
        return Integer.compare(song1.year, song2.year);
    case RANK_SORT:
        System.out.println("test");
        return Integer.compare(song1.rank, song2.rank);
    case ARTIST_SORT:
        System.out.println("test");
        return song1.artist.compareTo(song2.artist);
    case TITLE_SORT:
        System.out.println("test");
        return song1.title.compareTo(song2.title);
    }
    throw new RuntimeException(
            "Practically unreachable code, can't be thrown");
    }

}

Answer 1

After you output the filtered collection, your program doesn't terminate because you are still in a while loop looking for the next user input line. This is basically what your program is doing:

    while (input.hasNextLine()) {

        // stuff happens here

        System.out.println(collection.toString());

        /*
         * System.setOut(console); //changes output to print back to console Scanner outputFileScanner = new Scanner(outputFile); //inputs data from file while ((outputFileScanner.hasNextLine()))
         * { //while the file still has data System.out.println(outputFileScanner.nextLine()); //print } outputFileScanner.close(); out.close();
         */
    }