返回空指针异常但预期 MovieListException？

Question

所以我是运行一个JUnit测试，得到电影的评分(Hashmap:HashMap<String, Rating> movieList)) 但是如果没有针对电影的评级抛出 MovieListException。

JUNIT 预期与实际 https://imgur.com/a/mdQfJgT

学习抛出异常所以我不知道我做错了什么？

在评级class中我检查对象值是否为空，然后抛出MovieListException
在 MovieList class 中，此行出现空错误：Integer value = movieList.get(string).getRating(); 即使我正在捕获并返回 e 对象 (我认为它需要 RETURN？基于 JUNIT 测试？）

ISSUE: I am getting a null pointer instead of my MovieListException

测试class

    /* Test 5: Can't get a rating for an unrated movie
     */
    @Test(expected = MovieListException.class)
    public void nonexistentRating() throws MovieListException {
        String result = movies.getRating("The Ghost in the Invisible Bikini");

    }

电影列表class

public class MovieList {
private HashMap<String, Rating> movieList = new HashMap<String, Rating>();

public void addMovie(String string) {
    // TODO Auto-generated method stub
    movieList.put(string, new Rating(RatingType.NONE, null));
}



public String getRating(String string) throws MovieListException {
    // TODO Auto-generated method stub
    String ratingString = "";

    try {
        Integer value = movieList.get(string).getRating();

        if(value != null && value > 0) {
            for(int i = 0; i < value; i++) {
                ratingString += "*";
            } 
            return ratingString;
        }                   
    } catch(MovieListException e) {
        System.out.print(e.getMessage());
        return e.getMessage();
    }


    return "No rating";
}

public void setRating(String string, Rating rating) {
    // TODO Auto-generated method stub
    movieList.replace(string,  rating);
}

package movieListQuestion;

评分class

public class Rating {


private Integer ratingValue;
private RatingType typeValue;

public Rating(RatingType type, Integer rating) {
    this.ratingValue = rating;
    this.typeValue = type;
}   

public Integer getRating() throws MovieListException {
    if(this.ratingValue == null) {
        throw new MovieListException("No rating");
    }
    return this.ratingValue;
}

}

异常class

    package movieListQuestion;

/* A trivial exception class for the Movie List program.
 */
@SuppressWarnings("serial")
public class MovieListException extends Exception {

    public MovieListException() {
        super();
    }

    public MovieListException(String message) {
        super(message);
    }

}

已更新 MovieList 中的 getRating 方法 class

public String getRating(String string) throws MovieListException {
        // TODO Auto-generated method stub
        String ratingString = "";

            Integer value = movieList.get(string).getRating();

            if (!movieList.containsKey(string)) {
               throw new MovieListException("Movie not found");
            }

            if(value != null && value > 0) {
                for(int i = 0; i < value; i++) {
                    ratingString += "*";
                } 
                return ratingString;
            }                   


        return "No rating";
    }

Answer 1

在movieList.get(string).getRating()的NullPointerException很明显你搜索的电影不在movieList

当找不到电影时，您可能会决定抛出相同的 MovieListException。你可以这样做

if (!movieList.containsKey(string)) {
   throw new MovieListException("Movie not found");
}
//Rest of the code

//Or using Optional
Rating rating = Optional.ofNullable(movieList.get(string))
        .orElseThrow(() -> new MovieListException("Movie not found"));
Integer value = rating.getRating();

此外，您不应该在 getRating 方法中捕获 MovieListException

Answer 2

movieList.get(string).getRating();的movieList.get(string)是null。这意味着您在 movieList.

中没有名为 string 的电影

我认为你应该调用下面的方法

public void setRating(String string, Rating rating) {
    // TODO Auto-generated method stub
    movieList.replace(string,  rating);
}

从你的 junits 适当地。

返回空指针异常但预期 MovieListException？

Returning Null Pointer Exception BUT expected MovieListException?

java

junit

exception-handling

try-catch

nullpointerexception