java - 如果我的 Collection 中还没有某本书，如何将其添加到其中？ (java)

Question

我创建了一个 BookCollection 类，用于保存 Books(我创建的另一个类)。我正在尝试将两个 BookCollections 合并在一起，以制作 collection3。如果他们有重复的书，我会添加他们的库存并采取最低价格。如果它们不是重复的，我会将这本书添加到 Collection3 中。我了解如何处理重复的书籍，但我的循环不适用于独特的书籍。这是我的代码，我认为您可以在不查看涉及的所有其他代码的情况下理解我的目标:

 public static BookCollection merge(BookCollection collection1, 
                                  BookCollection collection2){
   //Make sure the collection is big enough
  int collection1Size = collection1.getSize();
  int collection2Size = collection2.getSize();
  int collection3Size = collection1Size + collection2Size;
  BookCollection collection3 = new BookCollection(collection3Size);

  //loop through collection one and add it to collection 3
  for (int i = 0; i < collection1Size; i++){
     Book collection1Book = new Book(collection1.objectAt(i));
     collection3.addBook(collection1Book);
  }

  //loop through collection two and add certain books to collection 3

  for (int q = 0; q < collection3Size; q++){
     if (collection3.objectAt(q) != null){
       Book collection3Book = new Book(collection3.objectAt(q));
      for (int j = 0; j < collection2Size; j++){
         if (collection2.objectAt(j) != null){
          Book collection2Book = new Book(collection2.objectAt(j));

        // if the book at collection 2 is the same as a book already in collection 3
           if (collection2Book.getIsbn().equals(collection3Book.getIsbn())){
               String BookISBN = collection2Book.getIsbn();

               //Handles the price of the book
               double price1 = collection2Book.getPrice();
               double price2 = collection3Book.getPrice();
               if (price1 > price2){
                 collection3.changePrice(BookISBN, price2);
                }
               if (price1 < price2){
                 collection3.changePrice(BookISBN, price1);
               } 
               // Handles the stock of the book
               int stock1 = collection2Book.getStock();
               collection3.changeStock(BookISBN, stock1);                  
           }

           // adds the rest of the new books from collection 2 to collection
           if (!(collection2Book.getIsbn().equals(collection3Book.getIsbn()))){
              if (collection3.getSize() < collection3Size){
                 collection3.addBook(collection2Book);
              }

           }
         }
       } 
      }
    }   
  return collection3;
}

首先，我将所有书籍从 Collection1 添加到 Collection3。然后我创建循环来检查 Collection2 和 Collection3 中是否有重复的书籍。伪代码很好，我只是不知道如何让我的程序看到 Collection2 中的一本书是唯一的。谢谢!

Answer 1

这是您的代码所采用的方法:

for each B3 in collection 3
    for each B2 in collection 2
        if B2 and B3 are the same book, then make some changes to the book
        if B2 and B3 are not the same book, then add it
    end
end

这并没有达到你想要的效果。为了判断集合 2 中的一本书是否是唯一的，您必须首先将该书与所有现有书籍进行比较。只有当你读完集合3中的所有书籍后，你才会知道是否应该将其添加为新书。您的代码不会这样做 - 因为“不是同一本书”逻辑出现得太早了。

正确的方法是这样的

for each B2 in collection 2
    for each B3 in collection 3
        if B2 and B3 are the same book, then make some changes to the book--and make a note that B2 has been found
    end
    if B2 has not been found then add it
end 

请注意，最后一次检查必须在内循环之外。