Question

我被分配了基于以下内容开发简单Java程序的任务：

编写算法以从列表中搜索保留的书籍副本（数组）使用线性搜索的书籍，然后将它们存储在使用插入算法开始新创建的数组。

我已经编写了算法，但由于以下代码的最后一行出现问题，我很难证明它：

package javaapplicationadt2;

public class Books
{

    public String ISBN;               // class properties
    public String title;
    public int copies;
    boolean reserved = true;

    public static void main(String[] args)
    {

        Books[] Book1 = new Books[1];
        Books[] Book2 = new Books[1];

        Book1[0].ISBN = "ISBN-00001";
        Book1[0].title = "Algorithms that torture minds";
        Book1[0].copies = 2;
        Book1[0].reserved = true;

        Book2[0].ISBN = "ISBN-00002";
        Book2[0].title = "Lecture Slides that defied practical Java Programming !";
        Book2[0].copies = 1;
        Book2[0].reserved = false;

        for (int i = 0; i < Book1.length; i++)
            if (Book1[i].reserved = true)
                for (int j = Book2.length - 1; j > 0; j++)
                    Book2[j] = Book2[j - 1];
     *Book2[0] = Book1[i].title;*   **(Incompatible types:
    Books cannot be converted to a String)**

    }
}

Answer 1

您的逻辑和代码约定存在很多错误

Java使用CamelCase作为编写方法，变量，类，包和常量名称的实践。类名应该是名词，大小写混合，每个内部单词的首字母大写。接口名称也应该像类名一样大写。看看Java Code conventions

Book[] bookArray = new Book[1];

返回您的代码。当你这样做

Book[] book1 = new Book[1]; //Create an Array of Books -> all elements are NULL
book1[0].ISBN = "ISBN-00001"; // book1[0] is NULL so a NullPointException will be throw

您必须初始化数组和/或为其分配对象

Book[] bookArray = new Book[1];
Book book = new Book();
Book[0] = book; //Now you have an Object Book at Book[0] and you can set the properties    
bookArray[0].ISBN = "ISBN-00001";

For和If ...如果没有定义块，则只执行下一行。即。

 if(true == bookArray[0].reserved)
     System.out.println("1");//This will be executed only if condition is true
     System.out.println("2"); //This will be executed no matter what

如果您只想在条件为真时执行代码，您必须：

if(true == bookArray[0].reserved){
     System.out.println("1");//This will be executed only if condition is true
     System.out.println("2"); //This will be executed only if condition is true
}

基于boolean Reserved = true将书籍从一个数组复制到另一个数组的“开头”

1 个答案: