Question

嗨，我必须编程：

public class Book {

    String title;
    boolean borrowed;

    // Creates a new Book
    public Book(String bookTitle) {
        // Implement this method
    }

    // Marks the book as rented
    public void borrowed() {
        // Implement this method
    }

    // Marks the book as not rented
    public void returned() {
        // Implement this method
    }

    // Returns true if the book is rented, false otherwise
    public boolean isBorrowed() {
        // Implement this method
    }

    // Returns the title of the book
    public String getTitle() {
        // Implement this method
    }

    public static void main(String[] arguments) {
        // Small test of the Book class
        Book example = new Book("The Da Vinci Code");
        System.out.println("Title (should be The Da Vinci Code): " + example.getTitle());
        System.out.println("Borrowed? (should be false): " + example.isBorrowed());
        example.rented();
        System.out.println("Borrowed? (should be true): " + example.isBorrowed());
        example.returned();
        System.out.println("Borrowed? (should be false): " + example.isBorrowed());
    }
}

输出应该是这样的：

Title (should be The Da Vinci Code): The Da Vinci Code
Rented? (should be false): false
Rented? (should be true): true
Rented? (should be false): false

我确实喜欢这个：

public class Book {
String title;
boolean borrowed;
// Creates a new Book
public Book(String bookTitle) {
// Implement this method
    String book=new String();
}
// Marks the book as rented
public void borrowed() {
// Implement this method
    borrowed=true;
}
// Marks the book as not rented
public void returned() {
// Implement this method
    borrowed=false;
}
// Returns true if the book is rented, false otherwise
public boolean isBorrowed() {
// Implement this method

    if (book=borrowed()){
        return true;
    }else if(book==returned()){
        return false;

    }
}

// Returns the title of the book
public String getTitle() {
// Implement this method
    return "The Da Vinci Code";

} 
public static void main(String[] arguments) {
// Small test of the Book class
Book example = new Book("The Da Vinci Code");
System.out.println("Title (should be The Da Vinci Code): " + example.getTitle());
System.out.println("Borrowed? (should be false): " + example.isBorrowed());
System.out.println("Borrowed? (should be true): " + example.isBorrowed());
System.out.println("Borrowed? (should be false): " + example.isBorrowed());
}
}

我认为我的代码通常很好，但是eclipse说：书籍无法解析为变量..在以下部分：

public boolean isBorrowed() {
// Implement this method

    if (book=borrowed()){
        return true;
    }else if(book==returned()){
        return false;

    }
}

如何更正前一部分代码中的问题？我是否对其余的代码做了更正？感谢

Answer 1

让我们放大这段代码：

if (book=borrowed()) {
        return true;
} else if(book==returned()) {
        return false;
}

首先要注意的是，在使用==检查相等性时，=运算符用于分配。例如，borrowed == true检查borrowed是否为真，borrowed = true将borrowed分配为真。

要注意的第二件事是，该书甚至不是isBorrowed中可用的变量，因为您没有将其保存为实例变量，就像您对borrowed和title所做的那样。

要注意的第三件事是您的支票book == borrowed()和book == returned()没有意义。 borrowed()和returned()是void方法，因此它们不返回任何内容，而book是一个字符串。您真正想要检查的是变量borrowed是真还是假：

if (borrowed == true) {
    return true;
} else if (borrowed == false) {
    return false;
}

可以简化为：

return borrowed;

您还需要更改main方法以在打印语句之间调用适当的方法：

System.out.println("Title (should be The Da Vinci Code): " + example.getTitle());
System.out.println("Borrowed? (should be false): " + example.isBorrowed());
example.borrowed();
System.out.println("Borrowed? (should be true): " + example.isBorrowed());
example.returned();
System.out.println("Borrowed? (should be false): " + example.isBorrowed());

Answer 2

您没有在book中定义isBorrowed()变量，因此它未定义，您应该收到编译器错误。

即使您有book变量，isBorrowed()方法也太复杂了。只需返回borrowed。

您还需要在分别拨打第二个borrowed()之前和之后拨打returned()和isBorrowed()，以进行正确的测试。

此外，在构造函数中设置title变量。

this.title = bookTitle;

并在title中返回getTitle()，而不是对其进行硬编码。

boolean部分代码在java

2 个答案: