我正在使用Musical Jukebox计划。我有两个主要类：Song.java和Playlist.java。 Song.java如下：
public class Song {
String name;
String title;
double length;
public Song(String name,String title,double length)
{
this.name=name;
this.title=title;
this.length=length;
}
public void setArtist(String songname)
{
name=songname;
}
public String getArtist()
{
return name;
}
public void setTitle(String songtitle)
{
title=songtitle;
}
public String getTitle()
{
return title;
}
public void setLength(double songlength)
{
length=songlength;
}
public double getLength()
{
return length;
}
public String toString()
{
return "Title: " + getTitle() + ", Artist: " + getArtist()
+ ", Track Length: " + getLength();
}
Playlist.java如下：
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;
@SuppressWarnings("serial")
public class Playlist<E extends Song> extends java.util.Vector<E> {
java.util.Iterator<E> itr = this.iterator();
String name;
ArrayList<Song> songList;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public ArrayList<Song> getSongList() {
return songList;
}
public void setSongList(ArrayList<Song> songList) {
this.songList = songList;
}
public void PlayList() {
name = "Untitled";
songList = new ArrayList<Song>();
}
public Playlist(String name) {
this.name = name;
songList = new ArrayList<Song>();
}
public Object getTitle()
{
return "Playlist Title";
}
public boolean addtoPlist(Song song1) {
songList.add(song1);
return true;
}
public Song getSong(int index) {
songList.trimToSize();
if(songList.size() >= index){
return songList.get(index);
}
else
return null;
}
public boolean hasTitle(String string) {
if( string.equals("Playlist Title"))
return true;
return false;
}
public boolean hasArtist(String string) {
if(string.equalsIgnoreCase("artist1"))
return true;
return false;
}
public Object numberOfSongs() {
// TODO Auto-generated method stub
return songList.size();
}
public Object numberOfArtists()
{
return 0;
}
public Object numberOfTitles()
{
return null;
}
public double playTime() {
return 0;
}
public Object findSong(Song song1) {
if(song1.equals("song1")&&song1.equals("song2")&&
song1.equals("song3")&&song1.equals("song4"))
itr.next();
return true;
}
public void sortByArtist()
{
}
public boolean removeFromPlist(Song str) {
songList.remove(str);
return true;
}
}
这是用于单元测试的playlisttest.java：
import junit.framework.TestCase;
import java.util.Vector;
public class PlaylistTest extends TestCase {
private Playlist<Song> aPlaylist;
private Song song1, song2, song3, song4, duplicate_song, nullSong;
public void setUp() {
aPlaylist= new Playlist<Song>("Playlist Title");
song1 = new Song("Artist1", "AA", 6.00);
song2 = new Song("Artist1", "BB", 3.50);
song3 = new Song("Artist2", "BB", 3.00);
song4 = new Song("Artist2", "CC", 5.50);
duplicate_song = new Song("ARTIST1", "TITLE1", 5.00); // Same song with song 1
nullSong = null;
}
protected void tearDown() throws Exception
{
super.tearDown();
}
protected void fillPlaylist() {
aPlaylist.addtoPlist(song1);
aPlaylist.addtoPlist(song2);
aPlaylist.addtoPlist(song3);
aPlaylist.addtoPlist(song4);
}
public void test_Constructor() {
assertNotNull(aPlaylist);
assertTrue(aPlaylist instanceof Vector);
assertTrue(aPlaylist.isEmpty());
}
public void test_getTitle() {
assertTrue(aPlaylist.getTitle().equals("Playlist Title"));
}
public void test_addtoPList() {
assertTrue(aPlaylist.isEmpty());
assertTrue(aPlaylist.addtoPlist(song1));
assertEquals(1, aPlaylist.size());
assertTrue(aPlaylist.addtoPlist(song2));
assertTrue(aPlaylist.addtoPlist(song3));
assertEquals(3, aPlaylist.size());
assertFalse(aPlaylist.addtoPlist(nullSong));
assertEquals(3, aPlaylist.size());
assertFalse(aPlaylist.addtoPlist(duplicate_song));
assertEquals(3, aPlaylist.size());
}
public void test_removeSong() {
fillPlaylist();
int size = aPlaylist.size();
assertFalse(aPlaylist.removeFromPlist(nullSong));
assertEquals(size, aPlaylist.size());
assertFalse(aPlaylist.removeFromPlist(new Song("Artist1", "Title1", 1.00)));
assertEquals(size, aPlaylist.size());
assertTrue(aPlaylist.contains(duplicate_song));
assertTrue(aPlaylist.removeFromPlist(duplicate_song)); // Removing "duplicate_song" is removing "song1"
assertEquals(size - 1, aPlaylist.size());
}
public void test_getSong() {
fillPlaylist();
assertTrue(aPlaylist.getSong(0) instanceof Song);
assertEquals(song1, aPlaylist.getSong(0));
assertEquals(duplicate_song, aPlaylist.getSong(0));
assertEquals(song2, aPlaylist.getSong(1));
assertEquals(song3, aPlaylist.getSong(2));
assertEquals(song4, aPlaylist.getSong(3));
}
public void test_hasTitle() {
fillPlaylist();
assertTrue(aPlaylist.hasTitle("Playlist Title"));
assertFalse(aPlaylist.hasTitle("wrong title"));
}
public void test_hasArtist() {
fillPlaylist();
assertTrue(aPlaylist.hasArtist("artist1"));
assertFalse(aPlaylist.hasArtist("wrong artist"));
}
public void test_numberOfSongs() {
fillPlaylist();
assertEquals(4, aPlaylist.numberOfSongs());
}
public void test_numberOfArtists() {
fillPlaylist();
assertEquals(2, aPlaylist.numberOfArtists());
}
public void test_numberOfTitles() {
fillPlaylist();
assertEquals(3, aPlaylist.numberOfTitles());
}
public void test_playTime() {
fillPlaylist();
assertTrue(aPlaylist.playTime() == 19.00);
}
public void test_findElement() {
fillPlaylist();
assertEquals(0, aPlaylist.findSong(song1));
assertEquals(1, aPlaylist.findSong(song2));
assertEquals(2, aPlaylist.findSong(song3));
assertEquals(3, aPlaylist.findSong(song4));
//assertEquals(-1, aPlaylist.findSong(new Song("Not", "There", 0)));
}
public void test_sortByArtist() {
// TODO: Assignment 6 -- create new test case here: sort by artist
}
public void test_sortByTitle() {
}
}
我想实现 numberOfTitles 方法来检索不同标题的数量，但我真的不知道如何使用不同的标题并返回计数（在我们的情况下，这是3，因为它可以看到如果有可能，你可以帮我解决这个问题吗？非常感谢您的帮助！
答案 0 :(得分：3)
您可以在Set中存储唯一标题，并在完成后获取此尺寸：
Set<String> uniqueSongs = new Set<>();
for (Song song : songList)
{
uniqueSongs.add(song.getTitle());
}
然后您可以使用uniqueSongs.size()获取唯一歌曲的数量。
如果您使用Java 8，也可以使用流（感谢Boris the Spider指出它）：
Set<String> uniqueSongs = songList.stream().map(Song::getTitle).collect(Collectors.toSet())