关于歌曲id的唯一性
package Player;
import java.util.Objects;
public class Song {
//属性:id,name,singer,format
private String id, name, singer, format;
//无参构造方法
public Song() {
}
//3参构造方法
public Song(String id, String name, String singer, String format) {
this.id = id;
this.name = name;
this.singer = singer;
this.format = format;
}
//get set方法
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSinger() {
return singer;
}
public void setSinger(String singer) {
this.singer = singer;
}
public String getFormat() {
return format;
}
public void setFormat(String format) {
this.format = format;
}
//hashcode()equals()方法
@Override
public boolean equals(Object o) {
//判断对象是否相等
if (this == o) {
return true;
}
//判断是否是属于子类
if (o.getClass() == Song.class) {
Song song = (Song) o;
return (song.getId().equalsIgnoreCase(id)) && (song.getName().equalsIgnoreCase(name)) && (song.getSinger().equalsIgnoreCase(singer)) && (song.getFormat().equalsIgnoreCase(format));
}
return false;
}
@Override
public int hashCode() {
int result = id.hashCode();
result = 31 * result + name.hashCode();
result = 31 * result + singer.hashCode();
result = 31 * result + format.hashCode();
return result;
}
//toString方法
@Override
public String toString() {
return "歌曲信息:" + "\n歌曲id:" + this.getId() + "\n歌曲名:" + this.getName() + "\n演唱者:" + this.getSinger() + "\n格式:" + this.getFormat() + "\n";
}
}
package Player;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class PlayList {
//属性:播放列表名称,歌曲集合
private String playListName;
private List<Song> musicList;
//无参构造方法
public PlayList() {
}
//有参构造
public PlayList(String playListName) {
this.playListName = playListName;
musicList = new ArrayList<>();
}
//get set方法
public String getPlayListName() {
return playListName;
}
public void setPlayListName(String playListName) {
this.playListName = playListName;
}
public List<Song> getMusicList() {
return musicList;
}
public void setMusicList(List<Song> musicList) {
this.musicList = musicList;
}
//添加歌曲
public void addToPalyList(Song song) {
boolean flag = false;
for (Song s : musicList) {
if (s.equals(song)) {
flag = true;
break;
}
}
if (flag) {
System.out.println(song.getName() + "已存在于此列表中,无法添加!");
} else {
musicList.add(song);
}
}
//修改歌曲信息(id)
public void updateSong(String id, Song song) {
//查询歌曲id是否存在
Song song1 = null;
for (Song s : musicList) {
if (s.getId().equalsIgnoreCase(id)) {
song1 = s;
break;
}
}
if (song1 == null) {
System.out.println("没有找到id为" + id + "的对应歌曲信息!");
} else {
//先移除,后添加
musicList.remove(song1);
musicList.add(song);
System.out.println("修改成功!");
}
}
//删除歌曲(id)
public void deleteSongById(String id) {
//先判断歌曲id是否在列表中
Song s = null;
for (Song song : musicList) {
if (song.getId().equalsIgnoreCase(id)) {
s = song;
break;
}
}
if (s != null) {
musicList.remove(s);
System.out.println("该歌曲已从列表中删除!");
} else {
System.out.println("该歌曲不存在!");
}
}
//删除歌曲(根据歌曲名字,歌名不唯一,删除集合中多个元素)
public void deleteSongByName(String name) {
//使用迭代器遍历修改
int n = musicList.size();
Iterator<Song> iterator = musicList.iterator();
while (iterator.hasNext()) {
Song song = iterator.next();
if (name.equalsIgnoreCase(song.getName())) {
//注意不能用List的remove方法
iterator.remove();
}
}
int m = musicList.size();
if (m == n) {
System.out.println("该歌名的歌曲不存在!");
} else {
System.out.println("删除成功!");
}
}
//删除歌曲(根据歌曲演唱者,演唱者不唯一,删除集合中多个元素)
public void deleteSongBySinger(String singer) {
//使用迭代器遍历修改
int n = musicList.size();
Iterator<Song> iterator = musicList.iterator();
while (iterator.hasNext()) {
Song song = iterator.next();
if (singer.equalsIgnoreCase(song.getSinger())) {
//注意不能用List的remove方法
iterator.remove();
}
}
int m = musicList.size();
if (m == n) {
System.out.println("该歌手的歌曲不存在!");
} else {
System.out.println("删除成功!");
}
}
//删除歌曲(根据歌曲格式,格式不唯一,删除集合中多个元素)
public void deleteSongByFormat(String format) {
//使用迭代器遍历修改
int n = musicList.size();
Iterator<Song> iterator = musicList.iterator();
while (iterator.hasNext()) {
Song song = iterator.next();
if (format.equalsIgnoreCase(song.getFormat())) {
//注意不能用List的remove方法
iterator.remove();
}
}
int m = musicList.size();
if (m == n) {
System.out.println("该格式的歌曲不存在!");
} else {
System.out.println("删除成功!");
}
}
//显示播放列表中所有歌曲
public void displayAllSong() {
System.out.println("主播放列表中所有的歌曲:");
for (Song song : musicList) {
System.out.println(song);
}
}
//根据id找歌(唯一性)
public void searchSongById(String id) {
Song song = null;
for (Song s : musicList) {
if (s.getId().equalsIgnoreCase(id)) {
song = s;
break;
}
}
if (song == null) {
System.out.println("该列表中没有此歌曲!");
} else {
System.out.println("根据歌曲id查询到的歌曲信息为:");
System.out.println(song);
}
}
//根据歌名找歌(由于格式不同,可能出现同歌名情况)
public void searchSongByName(String name) {
List<Song> list = new ArrayList<>();
for (Song s : musicList) {
if (s.getName().equalsIgnoreCase(name)) {
list.add(s);
}
}
if (list.size() == 0) {
System.out.println("该列表中没有此歌曲!");
} else {
System.out.println(name + "的歌曲信息为:");
for (Song s : list) {
System.out.println(s);
}
}
}
//根据格式找歌(不唯一性,所以返回值可能是多个,可以用集合表示)
public void searchByFormat(String format) {
List<Song> list = new ArrayList<Song>();
int count = 0;
for (Song song : musicList) {
if (song.getFormat().equalsIgnoreCase(format)) {
list.add(song);
count++;
}
}
if (list.size() != 0) {
System.out.println(format + "格式的歌曲有:" + count + "首");
int num = 1;
for (Song s : list) {
System.out.println("第" + num + "首" + "歌名为:" + s.getName());
}
} else {
System.out.println("该格式的歌曲不存在!");
}
}
//根据歌手找歌
public void searchBySinger(String singer) {
List<Song> list = new ArrayList<Song>();
int count = 0;
for (Song song : musicList) {
if (song.getSinger().equalsIgnoreCase(singer)) {
list.add(song);
count++;
}
}
if (list.size() != 0) {
System.out.println(singer + "的歌曲有:" + count + "首");
int num = 1;
for (Song s : list) {
System.out.println("第" + num + "首" + "歌名为:" + s.getName());
}
} else {
System.out.println(singer + "的歌曲不存在!");
}
}
}
package Player;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class PlayList {
//属性:播放列表名称,歌曲集合
private String playListName;
private List<Song> musicList;
//无参构造方法
public PlayList() {
}
//有参构造
public PlayList(String playListName) {
this.playListName = playListName;
musicList = new ArrayList<>();
}
//get set方法
public String getPlayListName() {
return playListName;
}
public void setPlayListName(String playListName) {
this.playListName = playListName;
}
public List<Song> getMusicList() {
return musicList;
}
public void setMusicList(List<Song> musicList) {
this.musicList = musicList;
}
//添加歌曲
public void addToPalyList(Song song) {
boolean flag = false;
for (Song s : musicList) {
if (s.equals(song)) {
flag = true;
break;
}
}
if (flag) {
System.out.println(song.getName() + "已存在于此列表中,无法添加!");
} else {
musicList.add(song);
}
}
//修改歌曲信息(id)
public void updateSong(String id, Song song) {
//查询歌曲id是否存在
Song song1 = null;
for (Song s : musicList) {
if (s.getId().equalsIgnoreCase(id)) {
song1 = s;
break;
}
}
if (song1 == null) {
System.out.println("没有找到id为" + id + "的对应歌曲信息!");
} else {
//先移除,后添加
musicList.remove(song1);
musicList.add(song);
System.out.println("修改成功!");
}
}
//删除歌曲(id)
public void deleteSongById(String id) {
//先判断歌曲id是否在列表中
Song s = null;
for (Song song : musicList) {
if (song.getId().equalsIgnoreCase(id)) {
s = song;
break;
}
}
if (s != null) {
musicList.remove(s);
System.out.println("该歌曲已从列表中删除!");
} else {
System.out.println("该歌曲不存在!");
}
}
//删除歌曲(根据歌曲名字,歌名不唯一,删除集合中多个元素)
public void deleteSongByName(String name) {
//使用迭代器遍历修改
int n = musicList.size();
Iterator<Song> iterator = musicList.iterator();
while (iterator.hasNext()) {
Song song = iterator.next();
if (name.equalsIgnoreCase(song.getName())) {
//注意不能用List的remove方法
iterator.remove();
}
}
int m = musicList.size();
if (m == n) {
System.out.println("该歌名的歌曲不存在!");
} else {
System.out.println("删除成功!");
}
}
//删除歌曲(根据歌曲演唱者,演唱者不唯一,删除集合中多个元素)
public void deleteSongBySinger(String singer) {
//使用迭代器遍历修改
int n = musicList.size();
Iterator<Song> iterator = musicList.iterator();
while (iterator.hasNext()) {
Song song = iterator.next();
if (singer.equalsIgnoreCase(song.getSinger())) {
//注意不能用List的remove方法
iterator.remove();
}
}
int m = musicList.size();
if (m == n) {
System.out.println("该歌手的歌曲不存在!");
} else {
System.out.println("删除成功!");
}
}
//删除歌曲(根据歌曲格式,格式不唯一,删除集合中多个元素)
public void deleteSongByFormat(String format) {
//使用迭代器遍历修改
int n = musicList.size();
Iterator<Song> iterator = musicList.iterator();
while (iterator.hasNext()) {
Song song = iterator.next();
if (format.equalsIgnoreCase(song.getFormat())) {
//注意不能用List的remove方法
iterator.remove();
}
}
int m = musicList.size();
if (m == n) {
System.out.println("该格式的歌曲不存在!");
} else {
System.out.println("删除成功!");
}
}
//显示播放列表中所有歌曲
public void displayAllSong() {
System.out.println("主播放列表中所有的歌曲:");
for (Song song : musicList) {
System.out.println(song);
}
}
//根据id找歌(唯一性)
public void searchSongById(String id) {
Song song = null;
for (Song s : musicList) {
if (s.getId().equalsIgnoreCase(id)) {
song = s;
break;
}
}
if (song == null) {
System.out.println("该列表中没有此歌曲!");
} else {
System.out.println("根据歌曲id查询到的歌曲信息为:");
System.out.println(song);
}
}
//根据歌名找歌(由于格式不同,可能出现同歌名情况)
public void searchSongByName(String name) {
List<Song> list = new ArrayList<>();
for (Song s : musicList) {
if (s.getName().equalsIgnoreCase(name)) {
list.add(s);
}
}
if (list.size() == 0) {
System.out.println("该列表中没有此歌曲!");
} else {
System.out.println(name + "的歌曲信息为:");
for (Song s : list) {
System.out.println(s);
}
}
}
//根据格式找歌(不唯一性,所以返回值可能是多个,可以用集合表示)
public void searchByFormat(String format) {
List<Song> list = new ArrayList<Song>();
int count = 0;
for (Song song : musicList) {
if (song.getFormat().equalsIgnoreCase(format)) {
list.add(song);
count++;
}
}
if (list.size() != 0) {
System.out.println(format + "格式的歌曲有:" + count + "首");
int num = 1;
for (Song s : list) {
System.out.println("第" + num + "首" + "歌名为:" + s.getName());
}
} else {
System.out.println("该格式的歌曲不存在!");
}
}
//根据歌手找歌
public void searchBySinger(String singer) {
List<Song> list = new ArrayList<Song>();
int count = 0;
for (Song song : musicList) {
if (song.getSinger().equalsIgnoreCase(singer)) {
list.add(song);
count++;
}
}
if (list.size() != 0) {
System.out.println(singer + "的歌曲有:" + count + "首");
int num = 1;
for (Song s : list) {
System.out.println("第" + num + "首" + "歌名为:" + s.getName());
}
} else {
System.out.println(singer + "的歌曲不存在!");
}
}
}
package Player;
import org.w3c.dom.ls.LSOutput;
import java.util.List;
public class Test {
//对歌曲类的测试
public void testSong() {
Song s1 = new Song("s0001", "青花瓷", "周杰伦", "MP3");
Song s2 = new Song("s0002", "红豆", "王菲", "WMA");
Song s3 = new Song("s0003", "山丘", "李宗盛", "APE");
Song s4 = new Song("s0004", "消愁", "毛不易", "FLAC");
Song s5 = new Song("s0005", "听海", "张惠妹", "APE");
System.out.println(s5);
//测试对象是否相等
// System.out.println(s1.equals(s2));
}
//对播放列表类中的方法测试
public void TestPlayList() {
//定义song对象
Song s1 = new Song("s0001", "青花瓷", "周杰伦", "MP3");
Song s2 = new Song("s0002", "红豆", "王菲", "WMA");
Song s3 = new Song("s0003", "山丘", "李宗盛", "APE");
Song s4 = new Song("s0004", "消愁", "毛不易", "FLAC");
Song s5 = new Song("s0005", "听海", "张惠妹", "APE");
Song s6 = new Song("s0006", "青花瓷", "周杰伦", "APE");
Song s7 = new Song("s0002", "暧昧", "王菲", "WMA");
//创建PlayLis对象
PlayList pl = new PlayList("主播放列表");
pl.addToPalyList(s1);
pl.addToPalyList(s2);
pl.addToPalyList(s3);
pl.addToPalyList(s4);
pl.addToPalyList(s5);
pl.addToPalyList(s6);
pl.addToPalyList(s7);
//显示播放列表
pl.displayAllSong();
//id找歌
pl.searchSongById("S0002");
//歌名找歌
// pl.searchSongByName("青花瓷");
//歌手找歌
// pl.searchBySinger("毛不易");
//格式找歌
// pl.searchByFormat("Ape");
//删除歌曲(id)
// pl.deleteSongById("02");
//删除歌曲(名字)
// pl.deleteSongByName("青花瓷");
//删除歌曲(歌手)
// pl.deleteSongBySinger("周杰伦");
//删除歌曲(格式)
// pl.deleteSongByFormat("ape");
//修改歌曲(id)
// pl.updateSong("02",s7);
// pl.displayAllSong();
}
public static void main(String[] args) {
Test t = new Test();
// t.testSong();
t.TestPlayList();
}
}歌曲id好像不是唯一性的,我添加两个Song对象,id一样,还是只能查询到一个?
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1回答
同学，你好！之所以只有一个id为s0002的歌曲，是因为在查询歌曲时，只要查询到符合条件的歌曲就跳出循环了，后面即使再有id相同的歌曲也查询不到了。
如果同学想要id也唯一，那么在添加歌曲时，可以判断一下id是否存在，如果不存在再添加歌曲。
另外，包名建议所有字母均小写。再有，同学贴出的代码中，PlayList类贴了两遍，没有PlayListCollection类
如果我的回答解决了你的疑惑，请采纳！祝学习愉快！
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