Question

我想知道如何格式化toString：我尝试使用printf和tring.format，但它希望我将String和int更改为Object[]

我希望它看起来像这样:(空格）

第一册______作者1 ________ 850

Book23 _____ Author2424 _____ 250

class Book
{
    private String title,author;
    private int numberOfPages;

    Book()
    {

    }

    public Book(String title, String author, int pages) {
        this.title = title;
        this.author = author;
        this.numberOfPages = pages;
    }

    public String toString()   
    {
        return(title + "%63s") + "\t" + (author + "%63s") + "\t" + numberOfPages;
        // It actually works but makes the "%63s" appear :o
    }
}

Answer 1

return String.format("%-30s%-30s%10d", title, author, numberOfPages);

Answer 2

String.format是正确的。您只需要将格式字符串设置为正确。

按如下方式更新toString()方法：

public String toString()   
{
    return String.format("%63s\t%63s\t%10d", title, author, numberOfPages);
}

第一个%63s将替换为title。

%63s将替换为author并添加空格，使其超过标题末尾63个字符。

%10d将替换为numberOfPages，并将数字填充为10位数。

Answer 3

我不确定您是否要将标题，作者和页数对齐在三个单独的列中。但是如果你这样做，你就无法通过覆盖Book的toString方法来实现这一点，因为它不知道集合中其他书籍的标题和作者名称有多长。

但是，您可以为图书声明自定义集合并覆盖其toString方法。这看起来如下：

class Main {

static class Book
{
    private String title,author;
    private int numberOfPages;

    public Book(String title,String author,int pages) {
        this.title = title;
        this.author = author;
        this.numberOfPages = pages;
    }

    public String toString()
    {
        return String.format("%-30s%-30s%10d", title, author, numberOfPages);
    }

}

static class Library {

    public static final int Margin = 2;

    private List<Book> books = new ArrayList<Book>();
    public void addBook(Book book){
        books.add(book);
    }
    private int longestTitle() {
        int result = 0;
        for (Book book : books) {
            result = book.title.length() > result ? book.title.length() : result;
        }
        return result;
    }
    private int longestAuthor() {
        int result = 0;
        for (Book book : books) {
            result = book.author.length() > result ? book.author.length() : result;
        }
        return result;
    }

    public String toString() {
        String result = "";
        for (Book book : books) {
            int titleLength = book.title.length();
            result += book.title;
            for (int i = longestTitle(); i > titleLength - Margin; i--){
                result += " ";
            }
            result += book.author;
            int authorLength = book.author.length();
            for (int i = longestAuthor(); i > authorLength - Margin; i--){
                result += " ";
            }
            result += book.numberOfPages + "\n";
        }
        return result;
    }
}

public static void main(String[] args) {
    Library lib = new Library();
    Book b1 = new Book("Knights of the round table", "King Arthur", 123);

    lib.addBook(b1);
    Book b2 = new Book("It", "Stephen King", 1345);
    lib.addBook(b2);
    Book b3 = new Book("A very, very, very, very long title that seems pointless", "Me", 112);
    lib.addBook(b3); 
//  System.out.println(b1);
//  System.out.println(b2);
//  System.out.println(b3);
//  They do not align separately
    System.out.println(lib.toString());
}

}

这个想法是查看哪个标题最长，并为每个要添加至少最长标题的填充的书添加。对于作者来说也是如此。

请注意，此代码编写得不是很好，但它应该足以传达这个想法。

格式化toString Java

3 个答案: