请老师看看为什么1-播放列表管理导出歌单功能和2-播放器管理中删除播放列表功能抛出异常
package com.imooc.Music;
//song类
public class Song {
private String id;
private String name;
private String singer;
public void setId(String id) {
this.id = id;
}
public String getId() {
return this.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 Song(String id, String name, String singer) {
this.setId(id);
this.setName(name);
this.setSinger(singer);
}
public Song() {
super();
// TODO Auto-generated constructor stub
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((id == null) ? 0 : id.hashCode());
result = prime * result + ((name == null) ? 0 : name.hashCode());
result = prime * result + ((singer == null) ? 0 : singer.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if(this==obj)
return true;
if(obj.getClass()==Song.class) {
Song s=(Song)obj;
return (this.getId().equals(s.getId()))&&(this.getName().equals(s.getName()))&&(this.getSinger().equals(s.getSinger()));
}
else return false;
}
@Override
public String toString() {
return "歌曲信息：id为:" + id + "，歌曲名称为：" + name + "，演唱者为：" + singer ;
}
}
package com.imooc.Music;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
//PlayList类
public class PlayList implements Serializable{
private String playListName;
private List<Song> musicList = new ArrayList<Song>();
Scanner sc = new Scanner(System.in);
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;
}
public PlayList(String playListName) {
this.setPlayListName(playListName);
this.setMusicList(musicList);
}
public PlayList(String playListName, List<Song> musicList) {
super();
this.setPlayListName(playListName);
this.setMusicList(musicList);
}
public PlayList() {
}
// 添加歌曲到播放列表的方法
public void addToPlayList(Song song) {
this.musicList.add(song);
}
// 显示播放列表歌曲的方法
public void displayAllSong() {
System.out.println(this.getPlayListName());
System.out.println("播放列表中的所有歌曲为：");
for (int i = 0; i < this.musicList.size(); i++)
System.out.println((Song)this. musicList.get(i));
}
// 通过id查询歌曲的方法
public Song searchSongById(String id) {
Song song = new Song();
boolean flag = false;
for (int i = 0; i < this.musicList.size(); i++) {
if ((this.musicList.get(i).getId()) .equals(id)) {
song = (Song)this. musicList.get(i);
flag = true;
break;
}
}
if (flag == false) // 编程常犯错误:将赋值当等于 (flag=false)
System.out.println("未找到该歌曲。");
return song;
}
// 通过歌名查询歌曲的方法
public Song searchSongByName(String n) {
Song song = new Song();
boolean flag = false;
for (int i = 0; i < musicList.size(); i++) {
if ((musicList.get(i).getName()).equals(n)) {
song = (Song) musicList.get(i);
flag = true;
break;
}
}
if (flag == false)
System.out.println("未找到该歌曲。");
return song;
}
// 修改歌曲的方法
public void updateSong(String id) {
boolean flag = false;
for (int i = 0; i < musicList.size(); i++) {
if ((musicList.get(i).getId()).equals(id)) {
flag = true;
System.out.println("修改的歌曲信息为：");
System.out.println((Song) musicList.get(i));
System.out.println("请输入修改后的歌曲名称");
(musicList.get(i)).setName(sc.next());
System.out.println("请输入修改后的歌曲演唱者");
(musicList.get(i)).setSinger(sc.next());
System.out.println("修改成功！");
break;
}
}
if (flag == false)
System.out.println("未找到该歌曲。");
}
// 通过id删除歌曲的方法
public void deleteSong(String id) {
for (int i = 0; i < musicList.size(); i++) {
if((musicList.get(i).getId()).equals(id))
musicList.remove(i);
}
System.out.println("删除后的播放列表为：");
for (int i = 0; i < musicList.size(); i++) {
System.out.println((Song)musicList.get(i));
}
}
//导出歌单
public void exportPlayList() {
try {
FileOutputStream fos=new FileOutputStream(this.getPlayListName()+"的歌单.txt");
ObjectOutputStream oos=new ObjectOutputStream(fos);
oos.writeObject(musicList);
oos.flush();
oos.close();
fos.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
package com.imooc.Music;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.Map.Entry;
import java.util.Scanner;
//PlayListCollection类
public class PlayListCollection {
Map<String,PlayList> playListMap=new HashMap<String,PlayList>();
public Map<String, PlayList> getPlayListMap() {
return playListMap;
}
public void setPlayListMap(Map<String, PlayList> playListMap) {
this.playListMap = playListMap;
}
public PlayListCollection(Map<String, PlayList> playListMap) {
this.setPlayListMap(playListMap);
}
//添加播放列表
public void addPlayList(PlayList playList) {
playListMap.put(playList.getPlayListName(), playList);
}
//删除播放列表
public void deletePlayList(PlayList playList) {
playListMap.remove(playList.getPlayListName());
}
//通过名字查询播放列表
public PlayList searchPlayListByName(String playListName) {
Set<Entry<String, PlayList>> entrySet = playListMap.entrySet();
PlayList p=new PlayList();
for(Entry<String, PlayList> entry:entrySet) {
if(entry.getKey().equals(playListName))
p=entry.getValue();
}
return p;
}
public boolean search(String playListName) {
Set<Entry<String, PlayList>> entrySet = playListMap.entrySet();
boolean flag=false;
for(Entry<String, PlayList> entry:entrySet) {
if(entry.getKey().equals(playListName))
flag=true;
}
return flag;
}
//显示所有播放列表名称
public void displayPlayListName(){
System.out.println("播放列表名称为:");
Set<Entry<String, PlayList>> entrySet = playListMap.entrySet();
for(Entry<String, PlayList> entry:entrySet) {
System.out.println(entry.getKey());
}
}
}
package com.imooc.Music;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;
import java.util.Map.Entry;
//Test类
public class TestDemo {
public void mainMenu() {
System.out.println("****************************************");
System.out.println(" **主菜单**");
System.out.println(" 1--播放列表管理");
System.out.println(" 2--播放器管理");
System.out.println(" 0--退出");
System.out.println("****************************************");
System.out.println("请输入对应数字进行操作：");
}
public void playListMenu() {
System.out.println("****************************************");
System.out.println(" **播放列表管理**");
System.out.println(" 1--将歌曲添加到主播放列表");
System.out.println(" 2--将歌曲添加到普通播放列表");
System.out.println(" 3--通过歌曲id查询播放列表中的歌曲");
System.out.println(" 4--通过歌曲名称查询播放列表中的歌曲");
System.out.println(" 5--修改播放列表中的歌曲");
System.out.println(" 6--删除播放列表中的歌曲");
System.out.println(" 7--显示播放列表中的所有歌曲");
System.out.println(" 8--导出歌单");
System.out.println(" 9--返回上一级菜单");
System.out.println("****************************************");
System.out.println("请输入对应数字对播放列表进行管理：");
}
public void playerMenu() {
System.out.println("****************************************");
System.out.println(" **播放器管理**");
System.out.println(" 1--向播放器添加播放列表");
System.out.println(" 2--从播放器删除播放列表");
System.out.println(" 3--通过名字查询播放列表信息");
System.out.println(" 4--显示所有播放列表名称");
System.out.println(" 9--返回上一级菜单");
System.out.println("****************************************");
System.out.println("请输入对应数字对播放器进行操作：");
}
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
PlayList p1 = new PlayList("主播放列表");
Map<String, PlayList> playListMap = new HashMap<String, PlayList>();
playListMap.put("主播放列表", p1);
Set<Entry<String, PlayList>> entrySet = playListMap.entrySet();
PlayListCollection player = new PlayListCollection(playListMap);
TestDemo t = new TestDemo();
while (true) {
t.mainMenu();
int x = sc.nextInt();
switch (x) {
case 1: {
while (true) {
t.playListMenu();
int y = sc.nextInt();
switch (y) {
case 1: {
System.out.println("请输入要添加的歌曲数量");
int num = sc.nextInt();
for (int i = 0; i < num; i++) {
System.out.println("请输入第" + (i + 1) + "首歌曲：");
System.out.println("请输入第" + (i + 1) + "首歌曲的id：");
String id = sc.next();
System.out.println("请输入第" + (i + 1) + "首歌曲的名称：");
String name = sc.next();
System.out.println("请输入第" + (i + 1) + "首歌曲的歌手：");
String singer = sc.next();
Song song = new Song(id, name, singer);
p1.addToPlayList(song);
}
continue;
}
case 2: {
System.out.println("请输入要添加的播放列表名称：");
String listName = sc.next();
boolean flag = player.search(listName);
if(!flag)
{System.out.println("该播放列表未找到，请先在播放器中添加该播放列表。");
continue;
}
if (flag) {
System.out.println("请输入要添加的歌曲数量");
int num = sc.nextInt();
while (true) {
for (int i = 0; i < num; i++) {
System.out.println("请输入第" + (i + 1) + "首歌曲：");
System.out.println("请输入第" + (i + 1) + "首歌曲的id：");
String id = sc.next();
if (p1.getMusicList().get(i).getId().equals(id)) {
player.searchPlayListByName(listName).addToPlayList(p1.searchSongById(id));
continue;
} else {
System.out.println("该歌曲在主播放列表中不存在，请输入该歌曲的其他信息");
System.out.println("请输入第" + (i + 1) + "首歌曲的名称：");
String name = sc.next();
System.out.println("请输入第" + (i + 1) + "首歌曲的歌手：");
String singer = sc.next();
Song song = new Song(id, name, singer);
player.searchPlayListByName(listName).addToPlayList(song);
}
}
break;
}
p1.displayAllSong();
player.searchPlayListByName(listName).displayAllSong();
continue;
}
}
case 3: {
System.out.println("输入播放列表名称：");
String listName = sc.next();
for (Entry<String, PlayList> entry : entrySet) {
if (entry.getKey().equals(listName)) {
System.out.println("请输入查询歌曲的id");
String id = sc.next();
System.out.println("查询到的歌曲信息为：");
System.out.println(entry.getValue().searchSongById(id));
break;
} else
System.out.println("该歌曲在" + listName + "中不存在。");
}
continue;
}
case 4: {
System.out.println("输入播放列表名称：");
String listName = sc.next();
for (Entry<String, PlayList> entry : entrySet) {
if (entry.getKey().equals(listName)) {
System.out.println("请输入查询歌曲的名称");
String name = sc.next();
System.out.println("查询到的歌曲信息为：");
System.out.println(entry.getValue().searchSongByName(name));
break;
} else
System.out.println("该歌曲在" + listName + "中不存在。");
}
continue;
}
case 5: {
System.out.println("请输入修改歌曲的id");
String id = sc.next();
for (Entry<String, PlayList> entry : entrySet) {
entry.getValue().updateSong(id);
}
continue;
}
case 6: {
System.out.println("请输入删除歌曲的id");
String id = sc.next();
for (Entry<String, PlayList> entry : entrySet) {
entry.getValue().deleteSong(id);
}
continue;
}
case 7: {
for (Entry<String, PlayList> entry : entrySet) {
entry.getValue().displayAllSong();
}
continue;
}
case 8:
p1.exportPlayList();
continue;
case 9:
}
break;
}
continue;
}
// **播放器管理**"
// 1--向播放器添加播放列表;
// 2--从播放器删除播放列表;
// 3--通过名字查询播放列表信息;
// 4--显示所有播放列表名称;
// 9--返回上一级菜单;
case 2: {
while (true) {
t.playerMenu();
int y = sc.nextInt();
switch (y) {
case 1: {
System.out.println("请输入要添加的播放列表名称");
String listName = sc.next();
PlayList p = new PlayList(listName);
player.addPlayList(p);
continue;
}
case 2: {
System.out.println("请输入要删除的播放列表名称");
String listName = sc.next();
for (Entry<String, PlayList> entry : entrySet) {
if (entry.getKey().equals(listName))
player.deletePlayList(entry.getValue());
}
continue;
}
case 3: {
System.out.println("请输入要查询的播放列表名称");
String listName = sc.next();
PlayList ps = player.searchPlayListByName(listName);
System.out.println("该播放列表存在！该播放列表的名称为：");
System.out.println(ps.getPlayListName());
continue;
}
case 4:
player.displayPlayListName();
continue;
case 9:
}
break;
}
continue;
}
case 0:
break;
}
break;
}
}
}0
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1回答
同学你好，删除播放列表中的歌曲报错如下：
这个错误是因为同学在遍历的过程中对播放列表进行了删除。所以删除播放列表时，建议在输入播放列表名称后，调用通过名字查询播放列表信息的方法查询播放列表是否存在，存在则删除，这样就不必对播放器进行遍历并删除，避免抛出异常。
2、导出歌单时报错如下：
这个异常是提示Song类需要实现序列化，如：
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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