使用printf会得到未对齐的列

Question

我正在尝试让我的程序以一种整洁的格式打印出数据，并使数据与列对齐。我尝试在我的类的toString方法中使用String.format，但它根本不对齐。我该怎么改呢？

package p01;

import java.text.DecimalFormat;

public class Book
{
DecimalFormat formatter=new DecimalFormat("##0.00");


private int bookNumber;
private String title;
private String author;
private int numberOfPages;
private String ISBN;
private double price;

public Book(int bookNumber, String title, String author, int numberOfPages,String ISBN, double price)
{
    super();
    this.bookNumber = bookNumber;
    this.title = title;
    this.author = author;
    this.numberOfPages = numberOfPages;
    this.ISBN = ISBN;
    this.price = price;
}

private final int validBookNumber(int bookNumber)
{
    if(bookNumber<0||bookNumber>7)
    {
        throw new IllegalArgumentException("The book number must be from 1 to 7");
    }
    return bookNumber;
}

private final String validTitle(String title)
{
    if (title==null)
    {
        throw new IllegalArgumentException("The title can't be null");
    }
    title.trim();
    if(title.length()==0)
    {
        throw new IllegalArgumentException("The title can't be blank");
    }
    return title;
}

private final String validAuthor(String author)
{
    if (author==null)
    {
        throw new IllegalArgumentException("The name of the author can't be null");
    }
    author.trim();
    if(author.length()==0)
    {
        throw new IllegalArgumentException("The name of the author can't be blank");
    }
    return author;
}
private final String validISBN(String ISBN)
{
    if (ISBN==null)
    {
        throw new IllegalArgumentException("The ISBN can't be null");
    }
    ISBN.trim();
    if(ISBN.length()==0)
    {
        throw new IllegalArgumentException("The ISBN can't be blank");
    }
    return ISBN;
}
private final int validNumberOfPages(int numberOfPages)
{
    if(numberOfPages<=0)
    {
        throw new IllegalArgumentException("The number of pages can't be less than 0");
    }
    return numberOfPages;
}
private final double validPrice(double price)
{
    formatter.format(price);
    if(price<=0)
    {
        throw new IllegalArgumentException("The price can't be less than 0");
    }
    return price;
}

public boolean equals(Object obj)
{
    if(obj != null && obj instanceof Book)
    {
        Book tempBook=(Book)obj;
        if(ISBN.equalsIgnoreCase(tempBook.ISBN))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    else
    {
        return false;
    }
}
public String toString()
{
    String str;
    str=String.format("%-4s %-11s %-11s %-11s %-11s %-3s",validBookNumber(bookNumber),validTitle(title),validAuthor(author),
                        validPrice(price), validNumberOfPages(numberOfPages), validISBN(ISBN));//I used the String formatter here
    return str;
}

}

package p01;
public class MJE_AB_List_Driver01
{

public static void main(String[] args)
{
    MJE_AB_List<Book>myBookList=new MJE_AB_List<Book>();
    Book book1=new Book(1,"To kill a Mocking Bird", "Harper Lee",336,"9780061120084", 16.99);
    Book book2=new Book(2,"Fahrenheit 451", "Ray Bradbury",256," 9781451673319", 15.99);
    Book book3=new Book(3,"1984", "George Orwell",304,"9780452262935", 16.00);
    Book book4=new Book(4,"Fight Club", "Chuck Palahniuk",224,"0-393-03976-5", 14.95);
    Book book5=new Book(5,"Invisible Monsters", "Chuck Palahniuk",304,"9780061120084", 16.99);
    Book book6=new Book(6,"Frankenstein", "Mary Shelly",256,"9781593081157", 6.95);
    Book book7=new Book(7,"The Grapes of Wrath", "John Steinbeck",528,"9780143039433", 17.00);

    myBookList.add(book1);
    myBookList.add(book2);
    displayList(myBookList);




}
public static void displayList(ParticularListInterface list)//This displays the list
{
    String headerString="Index    Book#    Title     Author     Price   Pages   ISBN";
    System.out.println(headerString +"\n");
    for(int index=0;index<list.size(); index++)
    {

        System.out.println(index+ " "+list.get(index));
    }
}

}

这是我得到的输出

Index    Book#    Title     Author     Price   Pages   ISBN

0 1    To kill a Mocking Bird Harper Lee  16.99       336            9780061120084
1 2    Fahrenheit 451 Ray Bradbury 15.99       256          9781451673319

这是我在Simon回答后的输出

Index    Book#    Title      Author     Price   Pages   ISBN

0  1    To kill a Mocking Bird                                       Harper Lee                16.99       336         9780061120084
1  2    Fahrenheit 451                                               Ray Bradbury              15.99       256          9781451673319

Answer 1

数据中的标题/作者值看起来比在String.format()调用中分配的空间长。将长度从11增加到更高的值，例如：

"%-4s %-40s %-25s %-11s %-11s %-3s"

Answer 2

格式字符串中的宽度是最小字符数，因此将填充至少该宽度的值，但如果它们更长，则将输出整个值。也就是说，除非您使用精度值指定最大字符数，例如：

String.format("%-4s %-11.11s %-11.11s %-11.11s %-11.11s %-3s");

这会将第2到第5个值截断为11个字符。但是请注意，它只是去掉了值，所以"To Kill a Mockingbird"变成了"To Kill a M"，这可能是您想要的，也可能不是您想要的。您可以增加宽度(如Simon建议的那样)和精度，也可以自己进行截断并添加省略号或其他东西，例如：

if (title.length() > 11)
    title = title.substring(0, 10) + "\u2026";