java - (初学者 Java 问题)为什么这段代码不起作用？

Question

(完整代码如下)我刚刚交了一个实验室上课，我们必须开设一门描述某本书的类(class)。我不知道如何做两件事。1. 如果有人为 'pages' 或 'suggestedRetailPrice' 输入小于零的值，该值必须设置为零。在此代码中，即使值为正值，该值也设置为 0。在:

---

if ( pages <= 0 )
    {
        pages = 0;
    }

---

如果我将第二个“0”设置为不同的数字，请编写代码，比如:

---

if ( pages <= 0 )
    {
        pages = 1;
    }

---

然后，无论您为“页面”输入什么，其值都将是 1。但如果您输入的值是负数，它不应该是 1 吗？我不明白我做错了什么。

我无法弄清楚的第二件事是在代码的底部，我们必须显示所有信息。我的老师希望我们将这本书是否平装显示为"is"或“否”，而不是“真”或“假”。我该怎么做呢？我试过像这样放置一个 if/else 语句:System.out.println("Paperback : "+ if (paperback = true) {Yes} if (paperback = false) {no}; )

没用，想不通。请参阅下面的完整代码。

---

public class Book {
    // Instance variables
    private String title;
    private String author;
    private int isbn;
    private int pages;
    private boolean paperback;
    private int suggestedRetailPrice;

    /**
     * Default contructor
     */
    public Book() {
        title = "";
        author = "";
        isbn = 0;
        pages = 0;
        paperback = false;
        suggestedRetailPrice = 0;
    }

    /**
     * book information
     */
    public Book(String whatIsTitle, String whoIsAuthor, int isbnCode,
            int numberOfPages, boolean isItPaperback,
            int theSuggestedRetailPrice) {
        title = whatIsTitle;
        author = whoIsAuthor;
        isbn = isbnCode;
        if (pages <= 0) {
            pages = 0;
        } else {
            pages = numberOfPages;
        }
        paperback = isItPaperback;
        if (suggestedRetailPrice <= 0) {
            suggestedRetailPrice = 0;
        } else {
            suggestedRetailPrice = theSuggestedRetailPrice;
        }
    }

    /**
     * @return title
     */
    public String getTitle() {
        return title;
    }

    /**
     * @return author
     */
    public String getAuthor() {
        return author;
    }

    /**
     * @return isbn
     */
    public int getIsbn() {
        return isbn;
    }

    /**
     * @return pages
     */
    public int getPages() {
        return pages;
    }

    /**
     * @return paperback
     */
    public boolean getPaperback() {
        return paperback;
    }

    /**
     * @return suggestedRetailPrice
     */
    public int getSuggestedRetailPrice() {
        return suggestedRetailPrice;
    }

    /**
     * title
     */
    public void setTitle(String whatIsTitle) {
        title = whatIsTitle;
    }

    /**
     * author
     */
    public void setAuthor(String whoIsAuthor) {
        author = whoIsAuthor;
    }

    /**
     * isbn code
     */
    public void setIsbn(int isbnCode) {
        isbn = isbnCode;
    }

    /**
     * number of pages
     */
    public void setPages(int numberOfPages) {
        if (pages <= 0) {
            pages = 0;
        } else {
            pages = numberOfPages;
        }
    }

    /**
     * is it paperback
     */
    public void setPaperback(boolean isItPaperback) {
        paperback = isItPaperback;
    }

    /**
     * suggested retail price
     */
    public void setSuggestedRetailPrice(int theSuggestedRetailPrice) {
        if (suggestedRetailPrice <= 0) {
            suggestedRetailPrice = 0;
        } else {
            suggestedRetailPrice = theSuggestedRetailPrice;
        }
    }

    /**
     * displays information
     */
    public void displayBook() {
        System.out.println("Title : " + title);
        System.out.println("Author : " + author);
        System.out.println("ISBN : " + isbn);
        System.out.println("Pages : " + pages);
        System.out.println("Paperback : " + paperback);
        System.out.println("Suggested price : " + suggestedRetailPrice);
    }
}

Answer 1

您在使用参数 numberOfPages 设置页面值之前检查页面值:

 title = whatIsTitle;
 author = whoIsAuthor;
 isbn = isbnCode;

 // pages is still at its initialzed value of 0 here.
 if ( pages <= 0 )
 {
     pages = 0;
 }
 else
 {
     pages = numberOfPages; // this will *never* be called
 } 

颠倒这个顺序。或者更好的是，检查参数值并使用它来设置您的页面值:

if (numberOfPages < 0) {
   pages = 0;
} else {
   pages = numberOfPages
}

对于您的第二个问题，创建一个名为 isPaperback 的字符串，如果平装书为真，则将其设置为输出字符串的"is"字符串，否则为“否”，然后在需要时显示该字符串。或者将您的 System.out.println("yes") 放入 if block 中以测试平装书的值(value)。

即，

if (paperback) {
   System.out.println(...);
} else {
   System.out.pringln(...);
}