-1
我有一種方法可以使用掃描器和分隔符來讀取五種股票的文本文件。我也有一種方法，它應該採用雙乘法器和一系列庫存對象，並用該乘數來改變價格。讀取庫存文件的方法正常工作，但是，當我試圖通過文件讀取方法更改已分配值的庫存對象時，它不會更改價格。在我使用方法updateStocks（）之後，我測試了股票[1]，看看這個值是否已經改變，但沒有。爲什麼updateStocks（）不改變價格？
後，我運行此：
public class Main {
public static void main (String args[]) {
// stock object with which to call methods
Stock theStock = new Stock("", "", 0);
// this array holds the stocks to be read
Stock[] stocks = new Stock[100];
// here is the multiplier I am attempting to use
double multiplier = 1/3;
// first I read in the stocks file
theStock.readStocksWithScanner(stocks);
// then I call the updateStockPrices method
theStock.updateStockPrices(multiplier,stocks);
// lastly, I test to see if the method has functioned correctly
System.out.println(stocks[1]);
}
}
This is my output:
Apple AAPLE 152.70
Alphabet GOOGLE 873.96
IBM IBM 194.37
Microsoft MSFT 65.67
Oracle ORCLE 62.82
Company name: Apple Stock symbol: AAPLE Stock Price: 152.7
Press any key to continue . . .
這裏是方法updateStockPrices：
// this is the method which does not seem to function as intended
public void updateStockPrices(double multiplier, Stock[] objects)
{
// I loop to the length of the array in the parameter
for(int i = 1; i < objects.length; i++)
{
// try to manipulate the stock
try{
double subtractThis = stocks[i].getPrice() * multiplier;
objects[i].setPrice(stocks[i].getPrice() - subtractThis);
}// and catch any null objects
catch(NullPointerException e){
// if null I then increment the counter
i++;}
// Is code missing in order for this to function as intended? or have I made a mistake?
}
}
這裏是stocks.java：
import java.util.Scanner ;
import java.util.InputMismatchException ;
import java.io.FileInputStream ;
import java.io.IOException ;
import java.io.FileNotFoundException ;
import java.io.PrintWriter ;
public class Stock {
private static final double MULTIPLIER = (1/3);
public static final String FILE_NAME = "stocks1.txt";
public String newFile = "stocks2.txt";
public static final String FORMAT = "%-10s%6s\t%.2f%n";
private PrintWriter writer = null;
private String name = "";
private String symbol = "";
private double price = 0;
protected Stock stocks[] = new Stock[100];
FileInputStream inputStream = null;
String workingDirectory = System.getProperty("user.dir");
String absolutePath = workingDirectory + "\\" + FILE_NAME;
public Stock(String aName, String aSymbol, double aPrice)
{
this.name = aName;
this.symbol = aSymbol;
this.price = aPrice;
}
// the fileReading method reads the stocks in
public void readStocksWithScanner(Stock[] stocks)
{
this.stocks = stocks;
String workingDirectory = System.getProperty("user.dir");
String absolutePath = workingDirectory + "\\" + FILE_NAME;
FileInputStream inputStream = null;
try{
inputStream = new FileInputStream(absolutePath);
}
catch (FileNotFoundException e)
{
System.out.println("File not found: " + FILE_NAME);
System.out.println("Exiting program.");
System.exit(0) ;
}
Scanner inputFile = new Scanner(inputStream);
int lineNumber = 1;
try{
while(inputFile.hasNextLine())
{
inputFile.useDelimiter(",");
String name = inputFile.next();
inputFile.useDelimiter(",");
String symbol = inputFile.next();
inputFile.useDelimiter("[,\\s]") ;
Double thePrice = inputFile.nextDouble();
inputFile.nextLine();
// here the stocks are given the values found in the text file and initialized above
stocks[lineNumber] = new Stock(name, symbol, thePrice);
// I print them out using a format constant, in order to ensure the method has functioned correcly
System.out.printf(FORMAT, name, symbol, thePrice);
// then I increment the lineNumber
lineNumber++;
}
// I close the stream and should be left with a partially filled array of stock items
inputStream.close();
}catch (IOException e) {
System.out.println("Error reading line " + lineNumber + " from file " + FILE_NAME) ;
System.exit(0) ;
}
catch(InputMismatchException e) {
System.out.println("Couldn't convert price to a number on line " + lineNumber) ;
System.exit(0) ;}
}
public void setName(String name)
{
this.name = name;
}
public void setSymbol(String symbol)
{
this.symbol = symbol;
}
public void setPrice(double aPrice)
{
this.price = aPrice;
}
public String getName()
{
return name;
}
public String getSymbol()
{
return symbol;
}
public double getPrice()
{
return price;
}
public boolean equals(Object other)
{
if(other.getClass() != getClass() || other == null)
{
return false;
}
Stock stock = (Stock) other;
{
if(stock.getName() == getName() && stock.getSymbol() == getSymbol() && stock.getPrice() == getPrice())
{
return true;
}
return false;
}
}
public String toString()
{
return "Company name: " + getName() + " Stock symbol: " + getSymbol() + " Stock Price: " + getPrice();
}
// this is the method which does not seem to function as intended
public void updateStockPrices(double multiplier, Stock[] objects)
{
// I loop to the length of the array in the parameter
for(int i = 1; i < objects.length; i++)
{
// try to manipulate the stock
try{
double subtractThis = stocks[i].getPrice() * multiplier;
objects[i].setPrice(stocks[i].getPrice() - subtractThis);
}// and catch any null objects
catch(NullPointerException e){
// if null I then increment the counter
i++;}
// Is code missing in order for this to function as intended? or have I made a mistake?
}
}
public void createStocks(int stockAmount)
{
Stock[] stocks = new Stock[stockAmount];
}
public void writeStocks(String fileName, Stock[] objects)
{
try{
writer = new PrintWriter(fileName);
}
catch(FileNotFoundException e){
System.out.println("Couldn't create file " + fileName);
System.exit(0);
}
for(Stock s: objects)
{
writer.printf(FORMAT, getName(), getSymbol(), getPrice());
if(objects == null)
writer.close() ;
}
}
public Stock[] getStocks()
{
return stocks;
}
}
i'm只是要注意，'抓（空指針異常）'，你倒是應該用'List'在這裏工作，而不是創造一個像'包含的實例array'奶酪的' Stock'和'null'。 – SomeJavaGuy
我目前還不能使用List，但是當我能夠使用List的時候，我會記錄下這些內容......我聽說List使得處理數組更容易 – mark1092