[英]Can't populate the ArrayList<> in a different class
我必须在Librarian
类中填充ArrayList<FictionBook>
,但是当我使用fictionBooks.add();
它不能识别变量fictionBooks
。 这是我当前的代码。 另外我不确定如何用add(String, String)
填充它。
public class FictionBook {
private String author;
private String title;
private static final int AVAILABLE = 1;
private static final int ONLOAN = 0;
public FictionBook(String theAuthor, String theTitle){
this.author = theAuthor;
this.title = theTitle;
}
public int borrow() {
System.out.println("The book is already borrowed.");
return ONLOAN;
}
public int returnB() {
System.out.println("The book was just returned.");
return AVAILABLE;
}
public String getAuthor() {
return author;
}
public String getTitle() {
return title;
}
}
我在这里创建arraylist:
import java.util.*;
public class Library {
private static final int CAPACITY = 200;
public ArrayList<FictionBook> fictionBooks = new ArrayList<FictionBook>();
public Library() {
//fictionBooks = new ArrayList<FictionBook>();
}
public void addBook(FictionBook book) {
fictionBooks.add(book);
}
public void deleteBook(FictionBook book) {
fictionBooks.remove(book);
}
public void borrowBook(FictionBook book) {
}
public void returnBook(FictionBook book) {
}
public void sort() {
Collections.sort(fictionBooks, String.CASE_INSENSITIVE_ORDER);
}
}
我需要在其中包含(“作者”,“标题”)的地方填充它:
public class Librarian {
public static void main(String[] args) {
fictionBooks.add("Jon", "Tiltle");
}
}
fictionBooks
属于Library
类。 您将必须首先实例化它。
public class Librarian {
public static void main(String[] args){
Library library = new Library();
library.addBook(new FictionBook("Jon", "Tiltle"));
}
}
您需要一个Library
的实例:
public class Librarian {
public static void main(String[] args){
Library library = new Library();
library.fictionBooks.add(new FictionBook("Jon", "Tiltle"));
}
}
或者使用Library
方法更好:
public class Librarian {
public static void main(String[] args){
Library library = new Library();
library.addBook(new FictionBook("Jon", "Tiltle"));
}
}
您将需要公开的方法说在图书馆和图书馆getBooks然后将使用图书馆象下面这样:
public static void main(String[] args){
Library library = ....;
library.getFictionBooks().add(new FictionBook("Jon", "Tiltle"));
}
注意之外,你或许应该想想间图书馆,图书管理员的关系,说图书馆有图书管理员,你可以库内撰写的图书管理员。
您可以通过在图书管理员类主方法中使用以下代码来添加书籍:
Library library = new Library();
FictionBook yourBookToAdd = new FictionBook("Jon", "Tiltle")
library.addBook(yourBookToAdd );
希望有帮助!
您的fictionBooks
ArrayList 属于您的Library
类。 这意味着您首先需要创建一个Library
的实例:
Library library = new Library();
然后,由于您的fictionBooks
变量是FictionBook
的列表, FictionBook
必须首先创建一个变量,然后才能将其添加到列表中,如下所示:
FictionBook fictionBook = new FictionBook("Jon", "Title");
现在,您可以访问新库的fictionBooks
变量,并将新创建的fictionBook
添加到其中:
library.fictionBooks.add(fictionBook);
但是由于您已经在Library
有了一个名为addBook(FictionBook)
,所以我建议像这样使用它:
library.addBook(fictionBook);
最后两个步骤可以压缩为一行,因此完成的代码如下所示:
public class Librarian {
public static void main(String[] args){
Library library = new Library();
//Creating and adding the Fiction Book to the list in a single line of code.
library.addBook(new FictionBook("Jon", "Title"));
}
}
这里已经载有正确答案,但我只是想进一步阐述一下,以防它可能帮助您更好地理解问题。 :)
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