如何使用 java 从多值数组列表中更新和删除元素/项目列表？

Question

这里是示例代码，

*ArrayList<Movie> list = new ArrayList<Movie>();
        
        list.add(new Movie("Force Awakens", 8.3, 2015));
        list.add(new Movie("Star Wars", 8.7, 1977));
        list.add(new Movie("Empire Strikes Back", 8.8, 1980));
        list.add(new Movie("Return of the Jedi", 8.4, 1983));*

/* etc.... */

*for (Movie empl :list) {
                System.out.println(empl);
        }*

我的数组列表将像（在控制台（eclipse）中输出）：

Movie [rating=8.7, name=Star Wars, year=1977]

Movie [rating=8.8, name=Empire Strikes Back, year=1980]

Movie [rating=8.4, name=Return of the Jedi, year=1983]

Movie [rating=8.3, name=Force Awakens, year=2015]

所以我的问题是如何使用 java 从列表中更新和删除上述任何一项。我应该在这里应用什么逻辑？？？？

P.S ：我尝试了 java remove() 命令但在下面抛出了一个异常：

Exception in thread "main" java.util.ConcurrentModificationException at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:937) at java.base/java.util.ArrayList$Itr.next(ArrayList.java:891) at mypackage.MainModule.main(MainModule.java:45)

Answer 1

ConcurrentModificationException 发生在不允许并发修改对象时。当一个人正在使用 Java Collection 类（在您的情况下为 ArrayList）时，通常会出现此异常。

1- 使用 Collections.synchronizedList() 获取列表的线程安全版本：

List<Movie> list = Collections.synchronizedList(yourMoviesArray);

然后在遍历列表时使用迭代器，并在迭代器上调用 remove() 方法来删除一个项目：

Iterator<Movie> it = list.iterator();
while(it.hasNext()) {
   if(condition) {
       it.remove();
   }
}

2- 使用 ArrayList 的线程安全变体是 CopyOnWriteArrayList.

CopyOnWriteArrayList<Movie> list = new CopyOnWriteArrayList<>(); 
list.add(); // add all your movies just like you add in a normal list

// conditional remove elemnts 
list.forEach(e -> {
   if (shouldRemove(e))
    list.remove(e);
});

Answer 2

您也可以尝试使用 lambda 表达式。

@Data
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
public class Movie {
    private String name;
    private Double rate;
    private Integer year;
}

class MovieCRUD {

    @Test
    public void deleteTest() {

        ArrayList<Movie> list = new ArrayList<Movie>();

        list.add(new Movie("Force Awakens", 8.3, 2015));
        list.add(new Movie("Star Wars", 8.7, 1977));
        list.add(new Movie("Empire Strikes Back", 8.8, 1980));
        list.add(new Movie("Return of the Jedi", 8.4, 1983));

        /*Equivalent to deleting star wars*/
        List<Movie> newList = list.stream()
                .filter(movie -> !movie.getName().equals("Star Wars"))
                .collect(Collectors.toList());//Only elements whose condition returns true will be retained

        /*
         * Movie(name=Force Awakens, store=8.3, year=2015)
         * Movie(name=Empire Strikes Back, store=8.8, year=1980)
         * Movie(name=Return of the Jedi, store=8.4, year=1983)
         */
        newList.forEach(System.out::println);

    }

   
    @Test
    public void updateTest() {

        ArrayList<Movie> list = new ArrayList<Movie>();

        list.add(new Movie("Force Awakens", 8.3, 2015));
        list.add(new Movie("Star Wars", 8.7, 1977));
        list.add(new Movie("Empire Strikes Back", 8.8, 1980));
        list.add(new Movie("Return of the Jedi", 8.4, 1983));


        List<Object> newList = list.stream()
                .map(movie -> movie.getRate() == 8.8 ? movie.setRate(7.8) : movie)
                .collect(Collectors.toList());
        /*
         *
         *   Movie(name=Force Awakens, store=8.3, year=2015)
         *   Movie(name=Star Wars, store=8.7, year=1977)
         *  Movie(name=Empire Strikes Back, store=7.8, year=1980) //Updated the movie's ratings
         *  Movie(name=Return of the Jedi, store=8.4, year=1983)
         */
        newList.forEach(System.out::println);

    }
}

Lambda 表达式对于过滤集合或数组中的数据非常有用。

如何使用 java 从多值数组列表中更新和删除元素/项目列表？

How to update and remove list of elements / item from a multivalued array list using java?

java

crud

arraylist