如何使用 indexOf 方法在 arraylist 中查找对象（具有自己的参数）的索引

Question

我有对象的 ArrayList Song。每个 Song 都有自己的参数，title, composer, duration,。我正在尝试编写将寻找 object Song 的 title 的方法，并将使用此参数给我 ArrayList 中对象的 INDEX。 songs是ArrayList的名字

public int findSong(String title) {
        int index = songs.indexOf(title);

        System.out.println(index);
        return index;
}

在这种情况下，方法正在寻找名称为 help 的对象，但是如何编写他将寻找具有参数 index 的对象的方法 title 等于 help。我只是想了解其中的逻辑）

 classname.findSong("help");

Answer 1

如果两首歌曲名称相同，您可以将 Song class 的相等函数覆盖为 return true：

public class Song{

    //Your other fields and functions ....

    @Override
    public boolean equals(Object obj) {
       if (!(obj instanceof Song))
            return false;
        if (obj == this)
            return true;

        Song s= (Song) obj;
        return s.getTitle().equals(this.title);
    }

}

Answer 2

试试这个代码：

public int findSong(String title) {
    int index = -1;
    // Iterate over the elements of the list
    for (Song song : songs) {
        if (song.getTitle().equals(title)) index = songs.indexOf(song);
    }
    // If you didn't know here we have if / else
    // if index == -1 print song not found else print the index
    System.out.println(index == -1 ? "Song not found: " + title : "Sound found at index " + index);
    // If song isn't found index is -1
    return index;
}

编辑： Max Zoom 在评论中说

How about the case where there is more then one song with given title?

代码：

public int[] findSong(String title) {
    List<Integer> indexesList = new ArrayList<>();
    // Iterate over the elements of the list
    for (Song song : songs) {
        if (song.getTitle().equals(title)) indexesList.add(songs.indexOf(song));
    }
    // If we have no songs return empty array
    if (indexesList.size() == 0) return new int[0];
    // Convert list to int array
    int[] indexes = new int[indexesList.size()];
    for (int i = 0; i < indexes.length; i++) {
        Integer integer = indexesList.get(i);
        if (integer != null) indexes[i] = integer.intValue();
        else indexes[i] = -1;
    }
    return indexes;
}

Answer 3

public int findSong(String searchtitle) {
        String str;
        int index = 0;
        for(Song s : songs){
            if(s.title.equalsIgnoreCase(searchtitle))
                return index;
            index++;
        }
    }

Answer 4

public int findSong(String title, List<Song> songs) {

    for (Song song : songs) {
      if (song == null || song.getTitle() == null) {
        continue;
      }
      if (song.getTitle().equals(title)) {
       int index = songs.indexOf(song);
       System.out.println(index);
       return index;
      }
    }
    return -1;

}

Answer 5

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

public class SongDriver
{

    public static void main(String[] args)
    {
        Song song1 = new Song();
        Song song2 = new Song();
        Song song3 = new Song();

        song1.setTitle("song1");
        song2.setTitle("help");
        song3.setTitle("song3");

        List<Song> songs = new ArrayList<Song>();
        songs.add(song1);
        songs.add(song2);
        songs.add(song3);

        for (int i = 0; i < songs.size(); i++)
        {
            Song song = songs.get(i);
            if (song.getTitle().equals("help"))
            {
                System.out.println("Help is found at index " + i);
            }
        }

    }

}

如何使用 indexOf 方法在 arraylist 中查找对象（具有自己的参数）的索引

How to find the index of the Object(that has its own parameters) in arraylist with using indexOf method

java

arraylist

collections

indexof