在同名数组中查找对象的索引，按值排序，然后更改其值

Question

我真的被困在代码的末尾，这是我迷路的地方。我的目标是从我制作的类（未显示）中创建一个对象数组。它存储它们的ISBN、标题和价格。该代码应该询问用户一个书名和ISBN#，如果它与数组中的任何一本书匹配，那么具有相同ISBN和书名的所有图书将从最低价格排序到最高价格，然后它们的所有价格将被改变为具有最低价格的图书的价格。我评论了我迷路的地方。多谢！

books类如下所示：class books{private String title；private int isbn；private int price；

        public Books(){
            title = "The Outsiders";
            ISBN = 1234;
            price = 14;
        }

        //regular constructor
        public Books(String T, int I, int P){
            title = T;
            ISBN = I;
            price = P;
        }
        //Copy Constructor
        public Books(Books aBook){
            this.title = aBook.title;
            this.ISBN = aBook.ISBN;
            this.price = aBook.price;
        }

这是我正在工作的班级的开始：

        //Beginning of ModifyBooks Class
    Books[] Library = new Books[10];

    Library[0] = new Books("blah", 1726374, 12.00);
    Library[1] = new Books("Lovely Bones", 111112, 20.00);
    Library[2] = new Books("Birds in a Fence", 111113, 13.00);
    Library[3] = new Books("Hunger Games", 111114, 14.50);
    Library[4] = new Books("Titanic", 738394, 12.5);
    Library[5] = new Books("Heroes", 7373849, 21.00);
    Library[6] = new Books(Library[1]);
    Library[7] = new Books(Library[1]);
    Library[8] = new Books(Library[2]);
    Library[9] = new Books(Library[3]);

    //Changing all prices of books
    for (int i = 0 ; i < Library.length ; i++){
        Library[i].price = i + 5;
    }

    //Keyboard configuration
    Scanner kb = new Scanner(System.in);

    System.out.println("Please enter a book's title:");
    String UserTitle = kb.nextLine();

    System.out.println("Please enter a book's ISBN Number:");
    int UserISBN = kb.nextInt();

    System.out.println("Your entered book's title is " + UserTitle + " and the ISBN is " + UserISBN);

    double[] sameBook = new double[10];
    int counter = 0;

这就是我的代码没有做我想做的事情的地方，我不知道如何让它做我上面描述的事情，但这里是我的尝试。

    for (int i = 0 ; i < Library.length ; i++ ){
        if (UserTitle.equalsIgnoreCase(Library[i].title) && UserISBN == Library[i].ISBN){
            sameBook[i] = Library[i].price;
            counter++;
        } 
        else {
            sameBook[i] = 0;
        }
    }
    double[] SmallerLibrary = new double[counter];

    for (int i = 0 ; i < sameBook.length ; i++){
        if (sameBook[i] != 0){
            SmallerLibrary[i] = sameBook[i];
        }
    }

    Arrays.sort(SmallerLibrary);

}

}

Answer 1

感谢大家的帮助，在杰夫·沃德和菲利普的帮助下，我想出了如何让我的程序做我想做的事情。新的工作代码在下面！：）

    //Beginning of ModifyBooks Class
    Books[] Library = new Books[10];

    Library[0] = new Books();
    Library[1] = new Books("Lovely Bones", 12345, 20);
    Library[2] = new Books("Birds in a Fence", 123456, 13);
    Library[3] = new Books("Hunger Games", 1234567, 14);
    Library[4] = new Books("Titanic", 12345678, 12);
    Library[5] = new Books("Heroes", 123456789, 21);
    Library[6] = new Books(Library[0]);
    Library[7] = new Books(Library[0]);
    Library[8] = new Books(Library[2]);
    Library[9] = new Books(Library[3]);

    //Changing all prices of books
    for (int i = 0 ; i < Library.length ; i++){
        Library[i].price = i + 5;
    }

    //Keyboard configuration
    Scanner kb = new Scanner(System.in);

    //Getting user information
    System.out.println("Please enter a book's title:");
    String UserTitle = kb.nextLine();

    System.out.println("Please enter a book's ISBN Number:");
    int UserISBN = kb.nextInt();

    System.out.println("Your entered book's title is " + UserTitle + " and the ISBN is " + UserISBN);

    int[] sameBook = new int[10]; //new array that will carry the index of each match
    int counter = 0; //tracks number of matches
    int globalMin = 200; //lowest price for the matches books, initialized at 200 so the program functions properly


    //Finding the matches in main array, and casting their indexes in another array
    for (int i = 0 ; i < Library.length ; i++ ){
        if (UserTitle.equalsIgnoreCase(Library[i].title) && UserISBN == Library[i].ISBN){
            sameBook[i] = i;
            counter++;
                if (Library[i].price < globalMin){
                    globalMin = Library[i].price;
                }
        }
        else {
            sameBook[i] = 0;
        }

    }

    //Creating a new array that only contains the amount of matches there are, containing their indexes
    int[] smallerLibrary = new int[counter];
    int j = 0;

    for (int i = 0 ; i < sameBook.length ; i++){
        if (sameBook[i] != 0){
            smallerLibrary[j++] = sameBook[i];
        }
    }

    //Text notifying user of matches and telling the, what the new prices will be
    for (int i = 0 ; i < smallerLibrary.length ; i++){
        System.out.println("Index number [" + smallerLibrary[i] + "] matches both the ISBN and title. The price was $" + Library[smallerLibrary[i]].price + " and is being changed to the lowest price of $" + globalMin + ".");
    }

    //Changing the prices from the matches to the lowest prices
    for (int i = 0 ; i < Library.length ; i++){
        if (UserTitle.equalsIgnoreCase(Library[i].title) && UserISBN == Library[i].ISBN){
        Library[i].price = globalMin;
        System.out.println("Change was made for index number "+i+".");
        }
    }

Answer 2

问题是，您正在迭代长度不同的数组，从而导致ArrayIndexOutofBounds。

如果你输入“可爱的骨头”，111112，那么你将有3个匹配。

相同的书长度总是10。

double[] sameBook = new double[10];

但SmallerLibrary长度为3（使用计数器初始化）

double[] SmallerLibrary = new double[counter];

因此，当迭代samebook.length时，索引最终将大于smallerlibrary.length从而导致异常。

for (int i = 0 ; i < sameBook.length ; i++){
    if (sameBook[i] != 0){
        SmallerLibrary[i] = sameBook[i];  // Exception thrown here
    }
}

您需要为SmallerLibrary中的值创建单独的索引。

  for (int i = 0, j = 0; i < sameBook.length; i++) {
     if (sameBook[i] != 0) {
        SmallerLibrary[j++] = sameBook[i];
     }
  }

Answer 3

请考虑以下策略：

1. 遍历数组中的每个book对象，并检查它是否与用户输入匹配。
2. 如果图书匹配，则将其索引存储在数组中以备以后使用，如果图书的价格低于先前设置的价格，则更新全局最小价格变量的值（控制第一次通过情况下的初始值）
3. 完成对列表的迭代后，使用存储每个匹配图书索引的数组，并使用全局最小价格变量更新它们的价格字段