java - 使用compareTo()比较对象的值

Question

我正在使用 Max-Heap 来存储 Song 类型的对象。歌曲具有标题和评级，如 Song 类中所示。我希望按评级比较 Song 对象，以便首先显示评级最高的歌曲。如果歌曲具有相同的评级，则应按标题的字母顺序进行比较。我现在所拥有的是当前以最高评级输出它，但不正确。

堆:

public class Heap<T extends Comparable<T>> {
private ArrayList<T> heap;

public Heap(){
    heap = new ArrayList<T>();
}
public int getPLoc(int i){
    return (i - 1) / 2;
}
public int getLCLoc(int i){
    return 2 * i + 1;
}
public int getRCLoc(int i){
    return 2 * i + 2;
}
public T getNodeAt(int i) {
    if(heap.get(i) == null) {
        System.out.println("Item does not exist.");
        return null;
    }else {
        return heap.get(i);
    }
}
public void addNode(T n) {
    heap.add(null);
    int index = heap.size() - 1;
    while(index > 0 && (getNodeAt(getPLoc(index)).compareTo(n)) < 0) { //Is this correct?
        heap.set(index, getNodeAt(getPLoc(index)));
        index = getPLoc(index);
    }
    heap.set(index, n);
}

歌曲:

public class Song implements Comparable<Song> {
private String title;
private String rating;

public Song(String t, String r) {
    title = t;
    rating = r;
}
public String getTitle(){
    return title;
}
public String getRating(){
    return rating;
}
// Need help here adding it to also compare by alphabetical title if songs have same ratings.
public int compareTo(Song s) {
    return rating.compareTo(s.getRating());
}

Answer 1

compareTo()方法返回 int具有以下值:

负如果 thisObject < anotherObject

零如果 thisObject == anotherObject

积极如果 thisObject > anotherObject

Check for value zero ，表示评级相同，然后选择 title comparison .

示例代码，可以调整

public int compareTo(Song s) {
    int val = rating.compareTo(s.getRating());
      if(val == 0){
         val = title.compareTo(s.getTitle());
      }
    return val;
}