问题
I am fairly new to object oriented programming, so I am still having some trouble grasping some of the basic concepts. So here I am trying to create a basic inventory program to keep track of stocks. Each stock contains couple details: company name, stock rating (AAA, AAa, Aaa, stuff like that), purchase price and numbers of shares. The program will ask user to input these details through command line prompt. And users can only input at most 12 stocks. If the user enters a stock twice, it will print out an error. And if the user has inputted one stock twice, it will also print out an error message.
Here is what I have done so far: Stock object
public class Stock {
private String companyName;
private String stockRating;
private int price;
private int numberOfShares;
public String getCompanyName() {
return companyName;
}
public int getStockRating() {
return stockRating;
}
public String getPrice() {
return price;
}
public int getNumberOfShares() {
return numberOfShares;
}
public Stock(String companyName, String stockRating, int price, int numberOfShares) {
super();
this.companyName = companyName;
this.stockRating = stockRating;
this.price = price;
this.numberOfShares = numberOfShares;
}
Now, I am trying to create stock inventory program
import java.util.*;
public class StockInvetory {
private static final int INVENTORY_SIZE = 12;
private Stock [] stocks;
public StockInvetory() {
stocks = new Stock [INVENTORY_SIZE];
}
private static void StockInventory() {
for (int i = 0; i<INVENTORY_SIZE; i++){
Scanner console = new Scanner(System.in);
System.out.println ("Stock's name:");
String stockName = console.next();
System.out.println ("Stock's rating");
String stockRating= console.next();
System.out.println ("Stock's price:");
int stockPrice = console.nextInt();
System.out.println ("Numbers of shares: ");
int numberShares= console.nextInt();
stocks [i]= new Stock(stockName, stockRatings, stockPrice, numberShares);
}
public static void main (String [] args){
StockInventory();
}
}
So my questions are the following:
The first stock object program should be okay, my problem is the stock inventory program. With this code, private Stock [] stocks, does it mean that the stock inventory program will store the info into an array? If it is, how do I store all the details associated with a particular stock, company name, price, etcs together. Do I have to create a multi-dimensional array in order of keep track of all the details? Like one row contains all the details about one stock, and second row contains details about another stock. And to determine if the user has entered one stock twice, do I use "equalsIgnoreCase" to do the comparison? I know I probably need to create another method for the stock Inventory.
Thank you very much in advance for your assistance.
回答1:
Once you read in the name, rating, price, and share count, you need to call the constructor on your class Stock to create an instance of the class and assign it to the next item in your stocks[] array.
Like so:
stocks[0] = new Stock( stockName, stockRating, stockPrice, numberShares);
Then you'll need to put the lines of code that you're using to read from the console, plus my line that creates the new Stock object into a loop so that you can read in all 12 stocks:
for( int i = 0; i < INVENTORY_SIZE; i++ )
{
System.out.println ("Stock's name:");
String stockName = console.next();
System.out.println ("Stock's rating");
String stockRating= console.next();
System.out.println ("Stock's price:");
int stockPrice = console.nextInt();
System.out.println ("Numbers of shares: ");
int numberShares= console.nextInt();
stocks[i] = new Stock( stockName, stockRating, stockPrice, numberShares);
}
Now, this isn't perfect, since it will require users to always enter a full set of 12 stocks, so you'll need to figure out how to let the user abort out of the loop if they're done, and you'll still have to add that error checking you want, to ensure that no duplicates are entered, but it should initialize your individual objects and assign eachh one to the array elements.
回答2:
private Stock [] stocks, does it mean that the stock inventory program will store the info into an array? If it is, how do I store all the details associated with a particular stock, company name, price, etcs together.
Your array is like a list of stocks. But just because its one object, doesn't mean it only contains one piece of data. It can hold Strings, ints, and other user-defined data types. Therefore, you can store pieces of data relating to the stock inside the Stock object.
public class Stock {
private String companyName;
private String stockRating;
private int price;
private int numberOfShares;
Those are all stored in each Stock object, and can be accessed by the getter methods you defined.
int stockdata = stocks[4].getPrice();
However, to initialize your Stock array, you want to create a new Stock object for each area, like so:
for(int i = 0; i < INVENTORY_SIZE; i++) {
stocks[i] = new Stock(foo, bar, lorem, ipsum);
}
The variables used here are just placeholders, so you can create your parameters by reading from the console like you're doing above.
These design principles for OOP should help you understand the relationship between data and containers.
For the second part of your question, you can look at just comparing one of the data values, like companyName, or implementing an interface like Comparable.
for(Stock s : stocks) {
if(stockName.equals(s.getCompanyName()) {
// ERROR!
}
}
回答3:
You may want to provide some way to break the loop in certain condition if user does not want to input all 12 information. However, it is totally on your requirements. In that case, you may have to use other options like List or vector.
Each object can have multiple variables , like in your case rating, price ,name and share which are bound to each object. So when you store an object in an index of array, you are actually storing all those information contained by that object in one single place. So in this case, you do not have to create multidimensional array.
You can override your equals method based on what defines the object as equal and use it to determine if same stock is provided again. This will return true if both object are same, otherwise false.
You can post your updated code and log here so that you can get suggestion regarding your exception
回答4:
In a real world scenario some questions come to mind:
- price shouldn't be an integer because a price is usually an amount in a specific currency. Check this money related question.
- Stock rating would be better represented using an Enum. See doc
来源：https://stackoverflow.com/questions/10859083/oop-java-creating-a-stock-inventory-program