如何使Main类中的变量可供其他类访问？

Question

For example I have a MovieDatabase class that contains a list of Movie objects. In my main code, I initialize all the objects in the MovieDatabase. However I wish to call this MovieDatabase in another class to access the library. How would I do this?

Do I add in get methods in my main code and return it? Or is there another way (eg. changing the list of objects to protected/public?)

Thanks!

Code's supposed to be 3 seperate classes, Main, MovieDatabase & Movie.

An instance of movieDatabase is initialized in Main. Upon construction, it calls loadMovieList() and populates the list from a text file. However I wish to call the same instantiation of movieDatabase from another class in order to access the movies, so that I do not have to repeat the loading.

public class Main {

public static void main(String[] args) {
    MovieDatabase movieDatabase = new MovieDatabase();
}

public class MovieDatabase {
ArrayList<Movie>movieList = new ArrayList<Movie>();
String fileAddress = "D:/Users/Mine/School/Java/CZ2002_Assignment/src/MovieDatabase/movieDatabase.txt";

public MovieDatabase()
{
    numOfMovie=0;
    loadMovieList();
}

public int getNumOfMovie() {
    return numOfMovie;
}

public void addMovieToList(Movie movie) {
    movieList.add(movie);
    numOfMovie++;
}

public Movie selMovieByID(int movieID) {
    int index=-1;
    for (Movie m : movieList) {
            index++;   
            if (m.getMovieID() == movieID)
                break;
    }
    return selMovieByIndex(index);
}


public Movie selMovieByIndex(int index) {
    return movieList.get(index);
}

public void loadMovieList()
{
    //loads through text file
    addMovieToList(new Movie(tempMovie));
    System.out.println("Movie Database loaded");
}

public class Movie{
private int movieID;
private String movieName;
private int movieDuration;  //in minutes;
private String movieRating; //G; PG; PG13; NC16; M18; R21;
private boolean has3D;
private boolean status; 
}

Answer 1

如果您有一个依赖于NameLibrary的类，则应通过构造函数或set方法注入它。

Answer 2

Firstly, its difficult to assess what issues you truly have without any code to show us. However you mention main method, as in public static void main(String args[]){};

this main method is designed specifically to run the application, your compiler needs that specific method, it is not designed to be used as an accessor method eg

public int getValue(){
return value;}

this is not the only reason you can't access the main method variable. main doesn't have a return type (due to the use of void) plus the idea of SCOPE (each method has a scope, any method that contains a variable can see that variable, but nothing outside of it can directly see it without a return type) you use scope to limit what can be accessed or what cannot be accessed outside of the methods or classes (thats why class variables usually will have private, in order to limit accessibility)

Answer 3

Create a getter-method which returns the list inside your NameLibrary . if your other class extends from NameLibrary you can call this getter-method with the object reference to your NameLibrary class.

Answer 4

If you want int x to be accessible from other classes, you write:

public class myClass{
    public int x = 0;
}

To access it from other classes, you simply write:

myClass.x ... (do something)