一旦达到限制就展开数组

Question

我有一个程序，我需要在一个数组中打印出几个 Movie object（仅由一个字符串表示）。我从一个文本文件开始，其中已经有五部电影，但在控制台中，如果 he/she 需要，我将允许用户扩展数组。（我不能在这个问题中使用数组列表）。我试图设计一个执行此操作的程序，但每次尝试添加新电影时都会出现越界异常。我还需要检查数组，看看里面是否有重复的电影 object？我怎样才能做到这一点？

问题：如何允许用户扩展数组并向列表中添加更多电影？我如何检查数组以查看其中是否已经有某个电影标题？

public class MovieDriver {

    //variable declaration
    static Movie[] movies = new Movie[5];
    static Scanner scan = new Scanner(System.in);
    static int input = 0;
    static String title = "";

    public static void main(String[] args) throws FileNotFoundException {

        //retrieves movie data
        getData();

        System.out.println("Welcome to the favorite movie program.");

    do{ 
        System.out.println("Press 1 to print the list, 2 to add another movie, 3 to end the program.");

        input = scan.nextInt();     

        switch(input) {

        case 1: 
            for(int i = 0; i < movies.length; i++)
            {
            System.out.println(movies[i].toString());
            }

            break;

        case 2:
            System.out.println("Please enter the movie you would like to add to the list:");
            title = scan.nextLine();
            movies = Arrays.copyOf(movies, movies.length+1);
            movies[movies.length] = new Movie(title);

            break;

        case 3:
            System.out.println("Program terminated.");

            break;



            }
        } while (input != 3);
    }

    // method to retrieve data
    public static void getData() throws FileNotFoundException {
        // reads in movie data
        File MovieData = new File("./src/Movies.txt");
        Scanner fileScanner = new Scanner(MovieData);
        int i = 0;

        // while there is a new line in the data, goes to the next one
        while (fileScanner.hasNextLine()) {
            String line = fileScanner.nextLine();
            Scanner lineScanner = new Scanner(line);
            String title = lineScanner.nextLine();

            // creates a movie
            movies[i] = new Movie(title);
            i++;
        }
    }
}

Answer 1

数组扩大1：

Movie[] temp = new Movie[movies.length + 1];
System.arraycopy(movies, 0, temp, 0, movies.length);
movies = temp;

要检查是否有重复的电影对象，请在您的 Movie class 中实施 equals。然后遍历现有的电影，并检查是否 movies[i].equals(newMovie).

Answer 2

要扩展数组，您必须重新创建一个所需大小的数组，并将前一个数组的内容复制到新数组中。

   static Movie[] movies = new Movie[5];

  // expanding
  Movie[] newMovieArray = new Movie[10];
  for(int i = 0; i < 5; i++){
       newMovieArray[i] = movies[i];
  }
  movies = newMovieArray;

Answer 3

第一个问题：IndexOutOfBound

不需要使用System.arraycopy()。您使用 Arrays.copyOf() 的正确方法。问题来自

movies = Arrays.copyOf(movies, movies.length+1); 
movies[movies.length] = new Movie(title);  // <--- here

调用 copyOf() 后，数组的新长度为 6。当您调用 movies[movies.length]=... 时，您尝试访问 7th 元素。只是做：

movies = Arrays.copyOf(movies, movies.length+1); 
movies[movies.length-1] = new Movie(title);  // it will set the last slot of the array

但是 Scanner 还有第二个问题。当您使用 nextInt() 扫描输入时，不会读取 end-of-line。这意味着如果您输入 2（添加电影），将读取 2，而不是 new-line。然后 new-line 被 title = scan.nextLine() 读取并且你有一个空标题...... 解决方案是：

case 2:
   scan.nextLine();  // <-- add this to "eat" the previous new-line
   System.out.println("Please enter the movie you would like to add to the list:");
   title = scan.nextLine();
   movies = Arrays.copyOf(movies, movies.length+1);
   movies[movies.length-1] = new Movie(title);
   break;

第二题：检查重复项

由于您只有一个 plain/native 数组并且电影之间没有排序，您可以实现一个简单的 for 循环，例如：

case 2:
   scan.nextLine();  // <-- add this to "eat" the previous new-line
   System.out.println("Please enter the movie you would like to add to the list:");
   title = scan.nextLine();
   if (!checkDuplicate(title)) {
      movies = Arrays.copyOf(movies, movies.length+1);
      movies[movies.length-1] = new Movie(title);
   }
   break;

并添加一个函数（假设有一个Movie#getTitle():

    private static boolean checkDuplicate(String title) {
        for (Movie m : movies) {
            if (title.equals(m.getTitle())) {
                return true;
            }
        }
        return false;
    }

一旦达到限制就展开数组

Expand array once it reaches limit

java

eclipse

arrays

variables

file

第一个问题：IndexOutOfBound

第二题：检查重复项