Question

我的任务是创建5个图书对象并存储在一个数组中，我没有问题！我能够使用println打印出对象的变量没问题，但是当我希望能够使用printf移动变量时，我不知道如何调用数组某个元素的特定变量。请帮助！

public class BookReport {    
    public static void main(String[] args){

        Book[] TheBooks = new Book[5] ;

        TheBooks[0] = new Book("Gone With The Wild", "Paul Mitchell", 1000) ;
        TheBooks[1] = new Book("Harry Toilet", "Donald Trump", 100) ;
        TheBooks[2] = new Book("Huckles Finn Berry", "SpiderMan", 500) ;
        TheBooks[3] = new Book("The Bad Habbit", "Nose Picker", 700) ;
        TheBooks[4] = new Book("Alien", "Mister Green", 600) ;


        System.out.printf("%10s  %20s %18s \n", "Book Title" , "Author", "Pages") ;
        System.out.printf("%s \n", "----------------------------------------------------") ;
        //This works but I cant justify the variables to align!!!
        System.out.println(TheBooks[0]) ;
    }
}

public class Book {
    private String title = "" ; 
    private String author = "" ;
    private int pages = 0 ;

    public Book(String title, String author, int pages){
        setTitle(title) ;
        setAuthor(author) ;
        setPages(pages) ;
    }

    public String getTitle(){
        return title ; 
    }
    public String getAuthor(){
        return author ;
    }

    public int getPages(){
        return pages ;
     }

     public void setTitle(String newTitle){
        title = newTitle ;
     }

    public void setAuthor(String newAuthor){
        author = newAuthor ;
    }

    public void setPages(int newPages){
        pages = newPages ;
    }

   public String toString(){
         return title + "       " + author + "        " + pages ;
   }

   public boolean equals(Book anotherBook){
        return ((title.equals(anotherBook.title)) && (author.equals     (anotherBook.author)) && 
            (pages == anotherBook.pages)) ;
   }
}

Answer 1

只需为要打印的各个字段调用getter：

System.out.printf("%10s  %20s %18s \n", "Book Title" , "Author", "Pages");
System.out.printf("%s \n", "----------------------------------------------------") ;
for (Book b : TheBooks) {
    System.out.printf("%10s  %20s %18s \n", b.getTitle(), b.getAuthor(), b.getPages());
}

顺便说一下，您将书籍数组命名为TheBooks，但不是将大写字母作为首字母命名为变量的Java约定。所以theBooks在这里会更好。

Answer 2

如果要调用数组中某个元素的特定变量。你可以用

java.util.Map

例如，您可以为要存储的所有对象设置 ID 。

HashMap<String, Book> h = new HashMap<>(); 
Book book = new Book("Gone With The Wild", "Paul Mitchell", 1000);
h.put(book.getTitle(), book); 
book = new Book("Harry Toilet", "Donald Trump", 100); 
h.put(book.getTitle(), book); 
book = new Book("Huckles Finn Berry", "SpiderMan", 500);
h.put(book.getTitle(), book);
book = new Book("The Bad Habbit", "Nose Picker", 700);
h.put(book.getTitle(), book);
book = new Book("Alien", "Mister Green", 600);
h.put(book.getTitle(), book);

// if you want to call it

Book b = h.get("exampletitle);

Answer 3

您还应该能够在toString方法中使用String.format（），以便拥有可重复使用的格式化版本。

@Override
public String toString(){
     return String.format("%10s  %20s %18s \n", title, author, pages);
}

P.S。我认为在包含equals（）的类中包含hashCode（）是一种好习惯。

如何访问数组中对象的变量？

3 个答案: