我有一种使用Scanner和delimiter读取五种股票的文本文件的方法。我还有一个方法，它应该采用双倍乘数和一组库存对象，并用该乘数改变价格。读取库存文件的方法正常运行，但是，当我尝试使用文件阅读方法更改已分配值的库存对象时，它不会更改价格。在我使用方法updateStocks（）之后，我测试stock [1]以查看该值是否已更改且未更改。
我跑完后：
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 . . .
这是方法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?
}
}
这里是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;
}
}
答案 0 :(得分：1)
简单测试
double multiplier = 1/3;
System.out.println(multiplier);
与
相比 double multiplier = 1/3f;
System.out.println(multiplier);