老师为什么我的查询放方法一直会返回null？

package player;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class PlayListCollection {
	private Map<String, PlayList> playListMap; // 存放播放列表集合
	// 构造方法

	public PlayListCollection() {
		this.playListMap = new HashMap<String, PlayList>();
	}

	// getter和setter方法
	public Map<String, PlayList> getPlayListMap() {
		return playListMap;
	}

	public void setPlayListMap(Map<String, PlayList> playListMap) {
		this.playListMap = playListMap;
	}

	/**
	 * 添加播放列表到播放器
	 * 
	 * @param playList 要添加的播放列表
	 */
	public void addPlayList(PlayList playList) {
		PlayList playList2 = searchPlayList(playList.getPalyListName());
		if (playList2 == null) {
			playListMap.put(playList.getPalyListName(), playList2);
		} else {
			System.out.println("歌单名为：" + playList.getPalyListName() + "的歌单已存在！");
		}
	}

	/**
	 * 删除播放器列表
	 * 
	 * @param playList 要删除的播放器列表
	 */
	public void delete(PlayList playList) {
		PlayList playList2 = searchPlayList(playList.getPalyListName());
		if (playList2 != null) {
			playListMap.remove(playList.getPalyListName());
		} else {
			System.out.println("歌单名为：" + playList.getPalyListName() + "的歌单不存在！");
		}
	}

	/**
	 * 通过名字查询播放器列表
	 * 
	 * @param playListName 要查询的播放列表
	 * @return 返回查询到的播放列表
	 */
	public PlayList searchPlayList(String playListName) {
		PlayList playList = null;
		Set<String> set = playListMap.keySet();
		for (String string : set) {
			if (string.equals(playListName)) {
				playList = (PlayList)playListMap.get(string);
				break;
			}
		}
		return playList;
	}

	// 显示所有播放列表的名称
	public void dispalyPlayListName() {
		Set<String> set = playListMap.keySet();
		System.out.println("播放列表名称为：");
		for (String string : set) {
			System.out.println(string);
		}
	}
}

package player;

public class Test {

	// 歌曲测试
	public void songTest() {
		Song song_1 = new Song("s001", "小星星", "A");
		Song song_2 = new Song("s002", "两只老虎", "B");
		Song song_3 = new Song("s003", "小太阳", "C");
		Song song_4 = new Song("s004", "小兔子", "D");
		// 测试toString方法
//		System.out.println(song_1);
		// 测试两个对象是否相等
//		System.out.println("song_1==song_2:"+song_1.equals(song_2));
//		System.out.println("song_1==song_4:"+song_1.equals(song_4));
		PlayList playList = new PlayList("主播放列表");
		// 添加歌曲到播放列表
		playList.addToPlayList(song_1);
		playList.addToPlayList(song_2);
		playList.addToPlayList(song_3);
//		playList.addToPlayList(song_4);
		// 显示所有歌曲
//		playList.displayAllSong();
//		
		// 通过ID查询歌曲
//		playList.searchSongById("s005");
//		
//		playList.displayAllSong();
		// 通过名字查询歌曲
//		playList.searchSongByName("小星");
//		
		// 更新歌曲信息
//		playList.updateSong("s001", song_4);
//		playList.displayAllSong();
		// 删除歌曲
//		playList.deleteSong("s006");
//		playList.displayAllSong();	
	}

	// 播放列表测试
	public void testPlayListCollection() {
		Song song_1 = new Song("s001", "小星星", "A");
		Song song_2 = new Song("s002", "两只老虎", "B");
		Song song_3 = new Song("s003", "小太阳", "C");
		Song song_4 = new Song("s004", "小兔子", "D");
		// 创建主播房列表
		PlayList mainPlayList = new PlayList("主播放列表");
		// 将歌曲添加到主播房列表
		mainPlayList.addToPlayList(song_1);
		mainPlayList.addToPlayList(song_2);
		mainPlayList.addToPlayList(song_3);
		// 将播放列表的歌曲添加到心得播放列表
		PlayList favouritePlayList = new PlayList("最喜爱的歌曲");
		favouritePlayList.addToPlayList(mainPlayList.getMusicList().get(0));
		favouritePlayList.addToPlayList(mainPlayList.getMusicList().get(1));
		favouritePlayList.addToPlayList(mainPlayList.getMusicList().get(2));
		PlayListCollection plc = new PlayListCollection();
		plc.addPlayList(mainPlayList);
		plc.addPlayList(favouritePlayList);
		plc.dispalyPlayListName();
		PlayList playList = plc.searchPlayList("最喜爱的歌曲");
		playList.displayAllSong();


	}

	public static void main(String[] args) {
		Test test = new Test();
		test.testPlayListCollection();

	}

}

package player;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class PlayList {
	private String palyListName; // 播放列表名称
	private List<Song> musicList; // 歌曲列表

	/**
	 * 构造方法
	 * 
	 * @param palyListName 播放列表名称
	 */
	public PlayList(String palyListName) {
		this.palyListName = palyListName;
		this.musicList = new ArrayList<Song>();
	}
	//getter和setter方法
	public String getPalyListName() {
		return palyListName;
	}

	public void setPalyListName(String palyListName) {
		this.palyListName = palyListName;
	}

	public List<Song> getMusicList() {
		return musicList;
	}

	public void setMusicList(List<Song> musicList) {
		this.musicList = musicList;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((musicList == null) ? 0 : musicList.hashCode());
		result = prime * result + ((palyListName == null) ? 0 : palyListName.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if(obj.getClass()==this.getClass()) {
			PlayList playList = (PlayList)obj;
			return playList.getPalyListName().equals(this.getPalyListName())&&playList.getMusicList().equals(this.getMusicList());
		}
		return false;
	}

	/**
	 * 将歌曲添加到播放列表
	 * 
	 * @param song 要添加的歌曲
	 */
	public void addToPlayList(Song song) {
		// 判断是否是重复歌曲
		boolean flag = false;
		for (Song song_1 : musicList) {
			if (song_1.equals(song)) {
				flag = true;
				break;
			}
		}
		if (flag) {
			System.out.println("此歌曲已经存在；");
			System.out.println(song);
			System.out.println("==========================");
		} else {
			musicList.add(song);
		}

	}

	/**
	 * 显示播放列表中歌曲
	 */
	public void displayAllSong() {
		for (Song song : musicList) {
			System.out.println(song);
		}
	}

	/**
	 * 通过ID查询歌曲的方法
	 * 
	 * @param id 查询的ID
	 * @return 歌曲信息
	 */
	public Song searchSongById(String id) {
		Song song = null;
		for (Song song2 : this.musicList) {
			if (song2.getId() == id) {
				song = song2;
				break;
			}
		}
		return song;
	}

	/**
	 * 通过名称查询歌曲的方法
	 * 
	 * @param name 歌曲名称
	 * @return 歌曲信息
	 */
	public Song searchSongByName(String name) {
		Song song = null;
		for (Song sg : this.musicList) {
			if (sg.getName() == name) {
				song = sg;
				break;
			}
		}
		return song;
	}

	/**
	 * 修改歌曲
	 * 
	 * @param id   需要修改的歌曲ID
	 * @param song 新的歌曲
	 */
	public void updateSong(String id, Song song) {
		Song son2= searchSongById(id);
		if(son2==null) {
			System.out.println("没有找到歌曲ID为："+id+"的歌曲");
		}else {
			musicList.remove(son2);
			musicList.add(song);
			System.out.println("歌曲更新成功！");
		}
	}

	/**
	 * 从播放列表删除歌曲
	 * 
	 * @param id 歌曲ID
	 */
	public void deleteSong(String id) {
		Song song=searchSongById(id);
		if(song==null) {
			System.out.println("没有找到歌曲ID为："+id+"的歌曲");
		}else {
			musicList.remove(song);
			System.out.println("删除成功！");
		}
	}

	// 按歌曲名进行排序
	public void sortBySongName() {

	}
}

package player;

public class Song {
	private String id; // id
	private String name;// 歌曲名字
	private String singer;// 演唱者
	// 构造方法

	public Song(String id, String name, String singer) {
		this.id = id;
		this.name = name;
		this.singer = singer;
	}

	// 属性的getter/setter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;
	}

	// 重写toString方法,输出歌曲歌曲信息
	@Override
	public String toString() {
		return "歌曲信息      歌曲ID：" + id + "    歌曲名称：" + name + "    演唱者：" + singer;
	}

	@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) {
		// 判断对象是否相等，相等直接返回true
		if (obj == this) {
			return true;
		}
		if (obj.getClass() == Song.class) {
			Song song = (Song) obj;
			return (song.getId().equals(id)) && (song.getName().equals(name)) 
					&& (song.getSinger().equals(singer));
		}
		return false;
	}

}

​

我就是在plc对象里面查询的啊，是在找不出问题了。老师你帮我看看代码

这里应该是playList吧？改过来