java - 我需要帮助从 2 个单独的 Arraylist 创建一个新的 Arraylist

Question

我需要填充我的totalprices ArrayList，但不知道如何。基本上我需要获取价格 ArrayList 和数量 ArrayList 并将它们相乘。然后获取这些值并将它们添加到totalprices ArrayList 中。然后找到总价格的最小值和最大值。我正在抓着我的头发试图弄清楚这个问题。请帮忙。谢谢!

我的代码:

import java.util.*;
import java.io.*;

public class Project01 {

public static void main(String[] args) {
    ArrayList<String> titles = new ArrayList<String>();//Declare the array lists that will be used.
    ArrayList<String> types = new ArrayList<String>();
    ArrayList<Double> prices = new ArrayList<Double>();
    ArrayList<Integer> quantities = new ArrayList<Integer>();
    ArrayList<Double> totalprices = new ArrayList<Double>();
    int count = 0;//Set the counter to zero.
    Scanner in = new Scanner(System.in);//Establish the scanner so user input can be properly read.
    String database = getFile(in);//Setting the file name variable from the method below that asks the user for the file's name.
    try {
        File file = new File(database);
        Scanner inputFile = new Scanner(file);
        System.out.println();
        System.out.println("Product Summary Report");
        System.out.println("------------------------------------------------------------");
        while (inputFile.hasNextLine()) {
            getTitle(titles, inputFile.nextLine());
            getQuantity(quantities, inputFile.nextInt());
            inputFile.nextLine();
            getPrice(prices, inputFile.nextDouble());
            inputFile.nextLine();
            getType(types, inputFile.nextLine());
            System.out.println("Title: " + titles.get(count));
            System.out.println(" Product Type: " + types.get(count));
            System.out.println(" Price: " + prices.get(count));
            System.out.println(" Quantity: " + quantities.get(count));
            System.out.println();
            count++;
        }
        System.out.println("-----------------------------------------------------------------");
        System.out.println("Total products in database: " + count);
        Integer index = getLargestQuantityTitle(quantities);
        System.out.println("Largest quantity item : " + titles.get(index) + " (" + types.get(index) + ")");
        ArrayList<Double> highestTotalDollarAmount = getTotalprices(quantities, prices);
        Double highestTotalDollarAmount = getHighestDollarAmount(totalprices);
        System.out.println("Highest total dollar item: $" + highestTotalDollarAmount);
        Integer index2 = getSmallestQuantityTitle(quantities);
        System.out.println("Smallest quantity item: " + titles.get(index2) + " (" + types.get(index2) + ")");
        System.out.println("Lowest total dollar item: ");
        System.out.println("-----------------------------------------------------------------");
        inputFile.close();
    } catch (IOException e) {
        System.out.println("There was a problem reading from " + database);

    }
    in.close();
}
private static String getFile(Scanner inScanner) {
    System.out.print("Enter database filename: ");
    String fileName = inScanner.nextLine();
    return fileName;
}
private static void getTitle(ArrayList<String> titles, String title) { //This method is creating the array list of the titles from the input file.
    titles.add(title);
}
private static void getType(ArrayList<String> types, String type) { //This method is creating the array list of the types from the input file.
    types.add(type);
}
private static void getPrice(ArrayList<Double> prices, double price) { //This method is creating the array list of the prices from the input file.
    prices.add(price);
}
private static void getQuantity(ArrayList<Integer> quantities, int quantity) { //This method is creating the array list of the quantities from the input file.
    quantities.add(quantity);
}
private static Integer getLargestQuantityItem(ArrayList<Integer> quantities){ //This method is determining the maximum value within the quantities array list.
    return Collections.max(quantities);
    }
private static Double getHighestPricedItem(ArrayList<Double> prices){ //This method is determining the maximum price within the prices array list.
    return Collections.max(prices);
}
private static Integer getHighestTotalDollarItem(ArrayList<Integer> prices){ //This method is determining the maximum total value, basically the highest quantity of the item multiplied by it's price.
    return Collections.max(prices);
}
private static Integer getSmallestQuantityItem(ArrayList<Integer> quantities){ //This method is determining the minimum value within the quantities array list.
    return Collections.min(quantities);
    }
private static Integer getLargestQuantityTitle(ArrayList<Integer> quantities){
    int index = 0;
    Integer largestQuantityMainVariable = getLargestQuantityItem(quantities);
    for (int i = 0; i < quantities.size(); i++) {
        if (quantities.get(i) != null && quantities.get(i).equals(largestQuantityMainVariable)) {
            index = i;
            break;
        }
    }
    return index;
}
private static Integer getSmallestQuantityTitle(ArrayList<Integer> quantities){
    int index2 = 0;
    Integer smallestQuantityMainVariable = getSmallestQuantityItem(quantities);
    for (int i = 0; i < quantities.size(); i++) {
        if (quantities.get(i) != null && quantities.get(i).equals(smallestQuantityMainVariable)) {
            index2 = i;
            break;
        }
    }
    return index2;
}
        private static ArrayList<Double> getTotalprices (List<Integer> quantities, List<Double> prices){
    ArrayList<Double> totalprices = new ArrayList<Double>();
    for (int i = 0; i < quantities.size(); i++) {
           totalprices.add(quantities.get(i) * prices.get(i));
      }
      return totalprices;

}
private static Double getHighestDollarAmount(ArrayList<Double> totalprices){ //This method is determining the maximum price within the prices array list.
    return Collections.max(totalprices);
}

}

输出应如下所示:

Enter database filename: proj1_input.txt

Product Summary Report
------------------------------------------------------------
Title: The Shawshank Redemption
    Product Type: DVD
    Price: 19.95
    Quantity: 100

Title: The Dark Knight
    Product Type: DVD
    Price: 19.95
    Quantity: 50

Title: Casablanca
    Product Type: DVD
    Price: 9.95
    Quantity: 137

Title: The Girl With The Dragon Tattoo
    Product Type: Book
    Price: 14.95
    Quantity: 150

Title: Vertigo
    Product Type: DVD
    Price: 9.95
    Quantity: 55

Title: A Game of Thrones
    Product Type: Book
    Price: 8.95
    Quantity: 100

-----------------------------------------------------------------
Total products in database: 6
Largest quantity item: The Girl With The Dragon Tattoo (Book)
Highest total dollar item: $[1995.0, 997.5, 1363.1499999999999, 2242.5, 547.25, 894.9999999999999]
Smallest quantity item: The Dark Knight (DVD)
Lowest total dollar item: Vertigo ($547.25)
-----------------------------------------------------------------

输入文件(.txt 文件):

The Shawshank Redemption
100
19.95
DVD
The Dark Knight
50
19.95
DVD
Casablanca
137
9.95
DVD
The Girl With The Dragon Tattoo
150
14.95
Book
Vertigo
55
9.95
DVD
A Game of Thrones
100
8.95
Book

Answer 1

进行编辑以在下面的评论中包含 knutknutsen 的答案以及 OP 的示例实现。

您是否考虑过使用 HashMap 来实现此目的？ HashMap 是一个列表对象，其中存储了 2 个对象。在下面的示例代码中，我将使用一个字符串作为“键”(这将是被索引的电影的标题)，并使用一个名为 StockInfo 的创建类作为“对象”。然后，您只需要对保存在某处或传递给所使用的类的标题的引用。

类似

public class Project01{
     static HashMap<String, StockInfo> movies = new HashMap<String, StockInfo>();
     static StockInfo movieWithMaxPrice = new StockInfo();
     static StockInfo movieWithMinPrice = new StockInfo();
     static StockInfo movieWithMaxQuantity = new StockInfo();
     static StockInfo movieWithMinQuantity = new StockInfo();

     public static void main(String[] args){
          int counter = 0;
          Scanner in = new Scanner(System.in);
          String database = getFile(in);
          try{
              File file = new File(database);
              Scanner inputFile = new Scanner(file);
              System.out.println();
              System.out.println("Product Summary Report");
              System.out.println("---------------------------------------");
              while(inputFile.hasNextLine()){
                   StockInfo movieInfo = new StockInfo();
                   getTitle(movieInfo, inputFile.nextLine());
                   getQuantity(movieInfo, inputFile.nextInt());
                   inputFile.nextLine();
                   getPrice(movieInfo, inputFile.nextDouble());
                   inputFile.nextLine();
                   getType(movieInfo, inputFile.nextLine());

                   /**This works because we over-rode the toString 
                     *call that java makes on an object when we try to 
                     *print out the object to the console.
                     */
                   System.out.println(movieInfo);
                   System.out.println();

                  /**The last thing we do is save the created  
                    *StockInfo to the saved HashMap
                    */
                   movies.put(movieInfo.getTitle(),movieInfo);
              }
              System.out.println("------------------------------------");
              System.out.println("Total products in database: "+movies.size());
              System.out.println("Largest Quantity item: "+movieWithMaxQuantity.getTitle()+" "+movieWithMaxQuantity.getQuantity());
              System.out.println("Highest total dollar item: "+movieWithMaxPrice.getTitle()+" $"+movieWithMaxPrice.getPrice());
              System.out.println("Smallest Quantity Item: "+movieWithMinQuantity.getTitle()+" "+movieWithMinQuantity.getQuantity());
              System.out.println("Lowest total dollar item: "+movieWithMinPrice.getTitle()+" $"+movieWithMinPrice.getPrice());
          } catch(IOException e){
              System.out.println("There was a problem reading from "+database);
          }
     }

     /**This method will return the fileName that is housing the 
       *database, which is provided to provided through an in console 
       *input from the user
       */
     private static String getFile(Scanner inScanner){
         System.out.print("Enter database filename: ");
         String fileName = inScanner.nextLine();
         return fileName;
     }

     /**This is a re-written method from the OP code, to read the line 
       *in the database file and fill the created StockInfo class with 
       *the title
       */
     private static void getTitle(StockInfo si, String lineToRead){
         si.setTitle(lineToRead);
     }

     /**This is a re-written method from the OP code, to read the line 
       *in the database file and fill the created StockInfo class with 
       *the quantity. This method also compares the given quantity 
       *with the saved quantities above Max and Min
       */
     private static void getQuantity(StockInfo si, int quantity){
         si.setQuantity(quantity);
         if(movieWithMaxQuantity.getQuantity()<quantity){
               movieWithMaxQuantity = si;
         }
         if(movieWithMinQuantity.getQuantity()>quantity){
               movieWithMinQuantity = si;
         }
     }
     /**This is a re-written method from the OP code, to read the line
       *in the database file and fill the created StockInfo class with
       *the price. This method also compares the given price with the
       *max and min StockInfo objects saved at the top of the class, 
       *to see if this is higher or lower then those. If it is
       *then is saves the new StockInfo object at its respective place
       *so that we always have a pointer towards the max and min
       */
     private static void getPrice(StockInfo si, double price){
         si.setPrice(price);
         if(movieWithMaxPrice.getPrice()<price){
              movieWithMaxPrice = si;
         }
         if(movieWithMinPrice.getPrice()>price){
              movieWithMinPrice = si;
         }
     }

     /**This is a re-written method from the OP code, that takes the
       *next line in the database and assigns it to the StockInfo as
       *its type
       */
     private static void getType(StockInfo si, String lineToRead){
         si.setType(lineToRead);
     }   

   }

/**This is the created class that will be used with the information
  *that gets provided
  */
class StockInfo{
    private String title = "";    //saved reference to the title
    private String type  = "";    //saved reference to the type
    /**saved reference to the price, pre filled at -1 to avoid null pointer exception*/
    private double price = -1;    
    /**saved reference to the quantity available, pre filled at -1 to avoid null pointer exception*/
    private int quantity = -1;


    /**This is the constructor, which needs nothing in this case*/
    public StockInfo(){} 

    /**This is the setter for our saved title string above*/
    public void setTitle(String title){
         this.title=title;
    }    

    /**This is the setter from our saved type string above*/
    public void setType(String type){
         this.type=type;
    }

    /**This is the setter for our saved price integer above*/
    public void setPrice(double price){
         this.price=price;
    }

    /**This is the setter for our saved quantity integer above*/
    public void setQuantity(int quantity){
         this.quantity=quantity;
    }

    /**This is the getter for the title*/
    public String getTitle(){
         return this.title;
    }

    /**This is the getter for the type*/
    public String getType(){
         return this.type;
    }

    /**This is the getter for the saved price*/
    public double getPrice(){
         return this.price;
    }

    /**This is the getter for the saved quantity*/
    public int getQuantity(){
         return this.quantity;
    }

    /**Overriding the toString call and making it return the info needed*/
    @Override
    public String toString(){
         return "Title: "+title+" Type: "+type+"  Price: "+price+" Quantity: "+quantity;
    }
}