java - 绑定(bind)不匹配错误 : The type is not a valid substitute

Question

绑定(bind)不匹配错误:类型不是有效的替代

任务:我想通过 PlayList 类将“Song 类对象”存储在 ImmutableSet 中。

我有三个类(class)。

public class ImmutableBinaryTree< T extends Comparable<T>> implements ImmutableSet<T> { }

public class Song { }


public class PlayList<T extends Comparable<T>> {
     private Song songs;  
     ImmutableSet<Song> immutableSet; // Bound Mismatch error occurring here

Answer 1

如果您要添加 Song至 ImmutableBinaryTree歌曲必须满足 ImmutableBinaryTree 上类型参数的界限，意味着它必须实现 Comparable接口(interface)，因为类型参数指定了边界 T extends Comparable<T> .

public class Song implements Comparable<Song>{

    @Override
    public int compareTo(Song arg0) {
        //provide implementation here
        //See effective java for appropriate implementation conditions
        return 0;
    }

}