继承和私有/公共变量

Question

所以我有三个课程:书籍,书籍和Allbooks.booksout和Allbooks是扩展/是书籍的子类.但是我有一个问题/疑问:

我在toString方法中从allBooks得到一个错误.说bookID等(即书中的所有变量)都设置为私有.我被告知你应该总是尽量避免公共变量,所以我犹豫不决.还有另外一种方法吗？或者将它们公之于众是最简单/最好的方式来处理这个问题？

这是代码:

图书

public class books {

private int bookID;
private String title;
private String author;


public books() {
}

public books(int bookID, String title, String author) {
    this.bookID = bookID;
    this.title = title;
    this.author = author;
}

public int getBookID() {
    return bookID;
}

public void setBookID(int bookID) {
    this.bookID = bookID;
}

public String getTitle() {
    return title;
}

public void setTitle(String title) {
    this.title = title;
}

public String getAuthor() {
    return author;
}

public void setAuthor(String author) {
    this.author = author;
}


public String addSpaces(String s, int w) {
    String spc = "";
    for (int i = 1; i <= (w - s.length()); i++) {
        spc = spc + " ";
    }
    return spc;
}

public class AllBooks extends books{
private String genre;
private String status;
private String Location;
private String condition;

Allbooks

public AllBooks(int bookID, String title, String author, String genre, String status, String Location, String condition ) {
    super(bookID, title, author);
    this.genre = genre;
    this.status = status;
    this.Location = Location;
    this.condition = condition;
}

public String getGenre() {
    return genre;
}

public void setGenre(String genre) {
    this.genre = genre;
}

public String getStatus() {
    return status;
}

public void setStatus(String status) {
    this.status = status;
}

public String getLocation() {
    return Location;
}

public void setLocation(String Location) {
    this.Location = Location;
}

public String getCondition() {
    return condition;
}

public void setCondition(String condition) {
    this.condition = condition;
}



    @Override
public String toString() {
    String stg = "";
    stg = stg + bookID + '\t' + title + addSpaces(title, 30) + author + addSpaces(author, 30) + genre + addSpaces(genre, 15) + status + addSpaces(status, 5) + Location + addSpaces(Location, 20) + condition;
    return stg;
}

    public String toString(int i){
    String stg = "";
    stg += bookID + "#" + title + "#" + author + "#" + genre + "#" + status + "#" + Location + "#" + condition + "#";
    return stg;
}

PS

如果这是一个愚蠢的问题,我很抱歉.这是一个学校项目,它应该在我假期之后,我现在正在这里,因此我不问我的老师.我确实在网上查了答案,但是我遇到的教程没有提到很多关于礼仪的内容.感谢您的帮助,和/或抱歉浪费您的时间.

Answer 1

使用现有的公共访问者.例如,getBookID()在子类中使用而不是尝试直接访问超类的私有字段.

@Override
public String toString() {
    String stg = getBookID() + '\t' + getTitle() 
        + addSpaces(title, 30) + getAuthor() 
        + addSpaces(author, 30) + getGenre() 
        + addSpaces(genre, 15) + getStatus() 
        + addSpaces(status, 5) + getLocation() 
        + addSpaces(Location, 20) + getCondition();
    return stg;
}

另一种方法是建立这个领域protected.但是,这允许可能任意数量的子类直接耦合到您的超类的表示.将数据封装在方法后面通常是优选的.

顺便提一下,您可能会发现String.format()很有用.有关语法,请参见格式字符串语法.