java - 迭代对象的自定义 LinkedList 类

Question

我创建了自己的 LinkedList 类，并创建了一个包含对象 Song 的 LinkedList (包含标题、艺术家、专辑、长度)。我遇到的错误是，当尝试迭代列表时，我收到“只能迭代 java.lang.Iterable 数组”。我认为我的问题是我正在迭代类实例，因此在我的链接列表类中缺少一些能够执行此类迭代的内容。但不确定我需要添加什么，提前致谢。

这是我尝试迭代的地方:

System.out.print("Enter song title: ");
String searchTitle = input.nextLine();
for ( Song i : list ){
    if ( i.getTitle() == searchTitle ){
        System.out.println(i);
        found = true;
    }
}
if ( found != true ){
    System.out.println("Song does not exist.");
}

我的 LinkedList 类

public class LinkedList {

private Node first;

private Node last;

public LinkedList(){
    first = null;
    last = null;
}

public boolean isEmpty(){
    return first == null;
}

public int size(){
    int count = 0;
    Node p = first;
    while( p != null ){
        count++;
        p = p.getNext();
    }
    return count;
}

public Node get( int i ){
    Node prev = first;
    for(int j=1; j<=i; j++){
        prev = prev.getNext();
}
    return prev;
}

public String toString(){
    String str = "";
    Node n = first;
    while( n != null ){
        str = str + n.getValue() + " ";
         n = n.getNext();
    }
    return str;
}

public void add( Song c ){
    if( isEmpty() ) {
        first = new Node(c);
        last = first;
    }else{
        Node n = new Node(c);
        last.setNext(n);
        last = n;
    }
}

歌曲类

public class Song {

    private String title;

    private String artist;

    private String album;

    private String length;

    private static int songCounter = 0;

    public Song(String title, String artist, String album, String length){
        this.title = title;
        this.artist = artist;
        this.album = album;
        this.length = length;
        songCounter++;
    }

    public String getTitle(){
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getArtist(){
        return artist;
    }

    public void setArtist(String artist) {
        this.artist = artist;
    }

    public String getAlbum(){
        return album;
    }

    public void setAlbum(String album){
        this.album = album;
    }

    public String getLength(){
        return length;
    }

    public void setLength(String length){
        this.length = length;
    }

    public static int getSongCounter(){
        return songCounter;
    }

    public int compareArtist(Song o){
        return artist.compareTo(o.artist);
    }

    public int compareTitle(Song o){
        return title.compareTo(o.title);
    }
    @Override
    public String toString(){
        return title +","+artist+","+album+","+length;
    }

Answer 1

错误消息非常明确:

Can only iterate over array of java.lang.Iterable.

这意味着您的类必须实现 Iterable界面。

对于您的情况，必须实现此功能的类必须是 LinkedList:

public class LinkedList implements Iterable<Song> {
    //implement methods in Iterable interface
}

您还可以升级您的 LinkedList 实现来处理通用元素，而不仅仅是 Song 对象引用。