按照这个运行 前面测试都没问题 运行到最后pl.addptPlayList(p)就提示空指针

这是PlayList类的

//将歌曲添加到普通播放列表

public void addptPlayList(PlayListCollection playListCollection) {

System.out.println("请输入您想添加的普通列表名称");

String str = s.next();

if(playListCollection.getPlayListMap().containsKey(str)) {

System.out.println("请输入歌曲id");

song.setId(s.next());

System.out.println("请输入歌曲名字");

song.setName(s.next());

System.out.println("请输入歌手名字");

song.setSinger(s.next());

}

else {

System.out.println("您的播放列表里没有该列表");

}

}

这是PlayListCollection类的

public class PlayListCollection {

private Map<String,PlayList> playListMap;

public PlayListCollection() {

}

public PlayListCollection(Map<String, PlayList> playListMap) {

super();

this.playListMap = playListMap;

}

public Map<String, PlayList> getPlayListMap() {

return playListMap;

}

public void setPlayListMap(Map<String, PlayList> playListMap) {

this.playListMap = playListMap;

}

Map<String, PlayList> plc = new HashMap<String, PlayList>();

Scanner s = new Scanner(System.in);

//添加播放列表

public void addPlayList(PlayList playList) {

PlayList pl = new PlayList();

System.out.println("请输入您要添加的播放列表名称");

String str = s.next();

pl.setPlayListName(str);

plc.put(str, pl);

System.out.println("添加成功");

}

//删除播放列表

public void deletePlayList(PlayList playList) {

System.out.println("请输入您要删除的播放列表");

plc.remove(s.next());

System.out.println("删除成功");

}

//通过名字查询播放列表

public PlayList searchPlayListByName(PlayList playliset) {

System.out.println("请输入您要查询的播放列表");

String k = s.next();

Set<String> keySet = plc.keySet();

for(String key:keySet) {

if(k.equals(key)) {

break;

}

}

System.out.println("您所查找的播放列表存在!\n该播放列表名称为："+k);

return plc.get(k);

}

//显示所有播放列表名称

public void displayListName() {

Iterator<String> a = plc.keySet().iterator();

if(a.hasNext()) {

Set<String> keySet = plc.keySet();

for(String key:keySet) {

System.out.println(key);

}

}

else

System.out.println("还没有播放列表");

}

}

这是测试类  

public static void main(String[] args) {

// TODO Auto-generated method stub

//PlayList pL = new PlayList("主播放列表",musicList);

PlayListCollection p = new PlayListCollection();

//pL.addToPlayList(song);

PlayList pl = new PlayList();

p.addPlayList(pl);

p.addPlayList(pl);

p.displayListName();

p.searchPlayListByName(pl);

   p.displayListName();

   p.deletePlayList(pl);

   p.displayListName();

   pl.addptPlayList(p);

}