java:不兼容的类型:推理变量T具有不兼容边界等式约束:下限:java.util.List〈>

8hhllhi2  于 2023-03-21  发布在  Java
关注(0)|答案(2)|浏览(273)

我尝试从流中获取列表,但出现了异常。
下面是一个Movie对象,其中包含一个对象列表。

public class Movie {

    private String example;
    private List<MovieTrans> movieTranses;

    public Movie(String example, List<MovieTrans> movieTranses){
        this.example = example;
        this.movieTranses = movieTranses;
    }
    getter and setter

以下是MovieTrans:

public class MovieTrans {

    public String text;

    public MovieTrans(String text){
        this.text = text;
    }
    getter and setter

我在列表中添加元素:

List<MovieTrans> movieTransList = Arrays.asList(new MovieTrans("Appel me"), new MovieTrans("je t'appel"));
List<Movie> movies = Arrays.asList(new Movie("movie played", movieTransList));
//return a list of MovieTrans
List<MovieTrans> movieTransList1 = movies.stream().map(Movie::getMovieTranses).collect(Collectors.toList());

我有这个编译器错误:

Error:(44, 95) java: incompatible types: inference variable T has incompatible bounds
    equality constraints: MovieTrans
    lower bounds: java.util.List<MovieTrans>
e37o9pze

e37o9pze1#

map调用

movies.stream().map(Movie::getMovieTranses)

Stream<Movie>转换为Stream<List<MovieTrans>>,您可以将其收集为List<List<MovieTrans>>,而不是List<MovieTrans>
要获取单个List<MovieTrans>,请使用flatMap

List<MovieTrans> movieTransList1 = 
    movies.stream()
          .flatMap(m -> m.getMovieTranses().stream())
          .collect(Collectors.toList());
xxhby3vn

xxhby3vn2#

表达式的类型为List<List<MovieTrans>>:它是getMovieTranses方法的结果的连接。
请改用flatMap

List<MovieTrans> movieTransList1 = movies.stream()
    .flatMap(m -> m.getMovieTranses().stream())
    .collect(Collectors.toList());

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