因此,我有三个班级:books,booksOut和Allbooks。 booksout和Allbooks是扩展类/是书籍的子类。但是我有一个问题/问题:

我从toString方法的allBooks中得到一个错误。说出bookID等(即book中的所有变量)设置为private。我被告知您应该始终避免使用公共变量,因此我很犹豫。还有另一种方法吗?还是将它们公开是处理此问题的最简单/最佳方法?

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;


全书

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;
}


聚苯乙烯

抱歉,这是一个愚蠢的问题。这是一个学校项目,应在我现在放假后放学,这就是我不问老师的原因。我确实在网上检查了答案,但是我遇到的教程并没有过多提及礼节。感谢您的帮助,和/或抱歉浪费您的时间。

最佳答案

使用现有的公共访问器。例如,在子类中使用getBookID()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;
}


另一种选择是将字段设置为protected。但是,这允许任意数量的子类直接耦合到超类的表示形式。通常最好将数据封装在方法后面。

顺便说一句,您可能会发现String.format()有用。有关语法,请参见Format String Syntax

关于java - 继承和私有(private)/公共(public)变量,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/17681184/

10-16 01:01