以下是作业的链接： pastelink.me/dl/bf6659#sthash.LtZIJpI7.dpuf
我需要完成SongCollection类才能到达第二个检查点。我对编码很陌生，而且我不是很擅长，所以我非常感谢你的所有答案！非常感谢。这是我到目前为止所做的工作：
主要课程：
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class GazillionSongs {
public static void main(String[] args){
try {
System.out.println("Hello. This program will sort and filter large databases of popular songs. Please enter an input file.");
Scanner file = new Scanner(System.in);
String userSelection = file.nextLine();
if (userSelection.toLowerCase().contains("gazillion")){
Scanner input = new Scanner(new File("C:/Users/julie_000/workspace/juliet/bin/agazillionsongs.txt"));
String user = input.nextLine();
Song songObject = new Song(user);
System.out.println(songObject.toString());
}
} catch (FileNotFoundException e) {
System.out.println("File not found");
}
}
}
歌曲课程：
import java.util.StringTokenizer;
public class Song {
private static int year;
private static int rank;
private static String artist;
private static String title;
public Song(String s){
StringTokenizer parseLine = new StringTokenizer(s, "\t");
String strYear = parseLine.nextToken();
year = Integer.parseInt(strYear);
String strRank = parseLine.nextToken();
rank = Integer.parseInt(strRank);
artist = parseLine.nextToken();
title = parseLine.nextToken();
}
public int getYear(){
return year;
}
public int getRank(){
return rank;
}
public String getArtist(){
return artist;
}
public String getTitle(){
return title;
}
public String toString(){
return String.format(year + "\t" + rank + "\t" + artist + "\t" + title);
}
}
SongCollection类：
import java.util.ArrayList;
public class SongCollection {
public SongCollection(ArrayList<Song> songs){
SongCollection objects = new SongCollection(songs);
}
public void filterYear(Range r){
}
public void filterRank(Range r){
}
public void filterArtist(String s){
}
public void filterTitle(String s){
}
public void sortYear(){
}
public void sortRank(){
}
public void sortArtist(){
}
public void sortTitle(){
}
public String toString(){
}
}
答案 0 :(得分：0)
用于对条目进行排序使用比较器接口，为了过滤您的条目，我建议您编写自己的过滤器。 我为你做了一个小例子：
You Entityclass Song，我只添加了另一个构造函数：
import java.util.StringTokenizer;
public class Song implements Comparable<Song>{
private int year;
private int rank;
private String artist;
private String title;
public Song(final int year, final int rank, final String title, final String artist) {
this.year = year;
this.rank = rank;
this.title = title;
this.artist = artist;
}
public Song(String s){
StringTokenizer stringTokenizer = new StringTokenizer(s, "\t");
String strYear = stringTokenizer.nextToken();
year = Integer.parseInt(strYear);
String strRank = stringTokenizer.nextToken();
rank = Integer.parseInt(strRank);
title = stringTokenizer.nextToken();
artist = stringTokenizer.nextToken();
}
public int getYear(){
return year;
}
public int getRank(){
return rank;
}
public String getArtist(){
return artist;
}
public String getTitle(){
return title;
}
public String toString(){
return String.format(year + "\t" + rank + "\t" + artist + "\t" + title);
}
public int compareTo(Song o) {
if(this.getYear() < o.getYear())
return -1;
if(this.getYear() > o.getYear())
return 1;
return 0;
}
}
SongCollection课程：
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import de.professional_webworkx.blog.cddb.comparators.ArtistComparator;
import de.professional_webworkx.blog.cddb.comparators.YearComparator;
import de.professional_webworkx.blog.cddb.model.Song;
public class SongCollection<T> extends ArrayList<T> {
/**
*
*/
private static final long serialVersionUID = -7754560588028902292L;
public SongCollection() {
}
public void addSong(final T song) {
this.add(song);
}
public T getSong(final int idx) {
return this.get(idx);
}
public List<T> sortByArtist() {
Collections.sort((List<Song>)this, new ArtistComparator());
return this;
}
public List<T> sortByYear() {
Collections.sort((List<Song>)this, new YearComparator());
return this;
}
}
正如您所看到的，我实现了两个方法，sortByArtist（）和sortByYear以及相应的Artist-和YearComparator（），我在下面发布：
ArtistComparator
import java.util.Comparator;
import de.professional_webworkx.blog.cddb.model.Song;
public class ArtistComparator implements Comparator<Song> {
public int compare(Song o1, Song o2) {
int ret = o1.getArtist().compareTo(o2.getArtist());
if(ret > 1) {
return 1;
}
if(ret < 1) {
return -1;
}
return 0;
}
}
YearComparator
import java.util.Comparator;
import de.professional_webworkx.blog.cddb.model.Song;
public class YearComparator implements Comparator<Song> {
public int compare(Song o1, Song o2) {
if(o1.getYear() < o2.getYear())
return -1;
if(o1.getYear() > o2.getYear())
return 1;
return 0;
}
}
现在，如果您想过滤条目，我建议使用IFilter接口：
的IFilter：
public interface IFilter<T> {
public boolean accept(T filter);
}
实现IFilter IF的BetweenFilter：
public class BetweenFilter<T extends Object & Comparable<T>> implements IFilter<T> {
private T lowBoundary;
private T highBoundary;
public BetweenFilter(final T lowBoundary, final T highBoundary) {
this.lowBoundary = lowBoundary;
this.highBoundary = highBoundary;
}
public boolean accept(T object) {
return lowBoundary.compareTo(object) <= 0 &&
highBoundary.compareTo(object) >= 0;
}
}
现在我们需要一个不错的小型Utils类，我将它命名为FilterUtils，以应用不同的过滤器：
FilterUtils： 此类获取带有条目的列表和应该应用的过滤器并遍历列表，如果当前值匹配则将添加到结果列表中。
import java.util.ArrayList;
import java.util.List;
public class FilterUtils {
public static <T> List<T> applyFilter(final List<T> list, final IFilter<T> filter) {
final List<T> filteredList = new ArrayList<T>();
for(final T val : list) {
if(filter.accept(val)) {
filteredList.add(val);
}
}
return filteredList;
}
}
现在，让我们尝试一下：
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.List;
import java.util.Scanner;
import de.professional_webworkx.blog.cddb.filter.BetweenFilter;
import de.professional_webworkx.blog.cddb.filter.BetweenYearFilter;
import de.professional_webworkx.blog.cddb.filter.FilterUtils;
import de.professional_webworkx.blog.cddb.filter.IFilter;
import de.professional_webworkx.blog.cddb.model.Song;
public class SongListManager {
public static void main(String[] args){
SongCollection<Song> collection = new SongCollection<Song>();
try {
Scanner input = new Scanner(new File("data/agazillionsongs.txt"));
String line = "";
while(input.hasNextLine()) {
String user = input.nextLine();
collection.add(new Song(user));
}
for(Song song : collection) {
System.out.println(song);
}
System.out.println("Filtered by Artist");
List<Song> filteredByArtist = collection.sortByArtist();
for(Song song : filteredByArtist) {
System.out.println(song);
}
IFilter<Song> betweenFilter = new BetweenFilter<Song>(new Song(1999, 1, "Hyper Hyper", "Scooter"), new Song(2001, 23, "Title", "DemoArtist"));
List<Song> applyFilter = FilterUtils.applyFilter(filteredByArtist, betweenFilter);
System.out.println("With applied Filter");
for(Song val : applyFilter)
System.out.println(val);
IFilter<Song> betweenYears = new BetweenYearFilter<Song>(2010, 2013);
List<Song> betweenYearsFiltered = FilterUtils.applyFilter(collection, betweenYears);
System.out.println("With applied years filter");
for(Song song : betweenYearsFiltered) {
System.out.println(song);
}
} catch (FileNotFoundException e) {
System.out.println("File not found");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
您可以在this Repository中找到代码。
希望这个示例代码能为您提供帮助。