Question

我尝试从流中获取列表，但我有一个例外。

这是带有对象列表的Movie对象。

$this->registerJs('
    $(".xxxxxxx").show();
    $("[name=rd_id]").change(function(){
        if($(this).val() == 0) {
            $(".xxxxxxx").hide();
        } else {
            $(".xxxxxxx").show();
        }
    });
');

这是MovieTrans：

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

我在列表中添加元素：

public class MovieTrans {

    public String text;

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

我有这个编译错误：

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());

Answer 1

<{p>}中的map电话

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

将Stream<Movie>转换为Stream<List<MovieTrans>>，您可以将其收集到List<List<MovieTrans>>，而不是List<MovieTrans>。

要获得一个List<MovieTrans>，请使用flatMap：

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

Answer 2

表达式的类型为List<List<MovieTrans>>：它是getMovieTranses方法结果的串联。

改为使用flatMap：

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

java：不兼容类型：推理变量T具有不兼容的边界等式约束：下界：java.util.List＆lt;＆gt;

2 个答案: