将文本文件中的数字读入 Java 中的 ArrayList
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Reading numbers from a text file into an ArrayList in Java
提问by
Can anyone show me a basic guideline for how to do this sort of thing? Would you use an Array or an ArrayList, and why? Anything else I've found online is too complicated to understand for my level of experience with Java. The file is a simple text file with seven decimal values per line, and contains three lines. Here is what I have so far and am just testing it to see if I'm doing the ArrayList properly. It keeps printing an empty ArrayList that is just two brackets.
谁能告诉我如何做这种事情的基本指南？你会使用 Array 还是 ArrayList，为什么？我在网上找到的任何其他内容都太复杂了，以我的 Java 经验水平无法理解。该文件是一个简单的文本文件，每行有七个十进制值，包含三行。这是我到目前为止所拥有的，我只是在测试它以查看我是否正确地执行了 ArrayList。它不断打印一个只有两个括号的空 ArrayList。
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
public class SalesAnalysis
{
public static void main (String[] args) throws FileNotFoundException
{
Scanner salesDataFile = new Scanner(new File("SalesData.txt"));
ArrayList<Double> salesData = new ArrayList<Double>();
while(salesDataFile.hasNextDouble())
{
salesData.add(salesDataFile.nextDouble());
}
salesDataFile.close();
System.out.println(salesData);
}
}
采纳答案by nullptr
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
public class SalesAnalysis
{
public static void main (String[] args) throws FileNotFoundException
{
Scanner salesDataFile = new Scanner(new File("SalesData.txt"));
ArrayList<Double> salesData = new ArrayList<Double>();
while(salesDataFile.hasNextLine()){
String line = salesDataFile.nextLine();
Scanner scanner = new Scanner(line);
scanner.useDelimiter(",");
while(scanner.hasNextDouble()){
salesData.add(scanner.nextDouble());
}
scanner.close();
}
salesDataFile.close();
System.out.println(salesData);
}
}
Read lines from file, then for each file get doubles using Scanner.
从文件中读取行，然后使用 Scanner 为每个文件获取双倍。
And for per line basis, you can just create Lists for every line, like:
对于每行，您可以为每一行创建列表，例如：
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
public class SalesAnalysis
{
public static void main (String[] args) throws FileNotFoundException
{
Scanner salesDataFile = new Scanner(new File("SalesData.txt"));
while(salesDataFile.hasNextLine()){
String line = salesDataFile.nextLine();
ArrayList<Double> salesData = new ArrayList<Double>();
Scanner scanner = new Scanner(line);
scanner.useDelimiter(",");
while(scanner.hasNextDouble()){
salesData.add(scanner.nextDouble());
}
scanner.close();
System.out.println(salesData);
}
salesDataFile.close();
}
}
As you are getting per line values inside first while() loop, you can do whatever with line.
当您在第一个 while() 循环中获取每行值时，您可以对 line 执行任何操作。
// number of values in file
int totalNumValues = 0;
// total sum
double totalSum = 0;
while(salesDataFile.hasNextLine()){
String line = salesDataFile.nextLine();
ArrayList<Double> salesData = new ArrayList<Double>();
// total values in this line
int numValuesInLine = 0;
// sum in this line
double sumLine = 0;
Scanner scanner = new Scanner(line);
scanner.useDelimiter(",");
while(scanner.hasNextDouble()){
double value = scanner.nextDouble();
sumLine = sumLine + value;
numValuesInLine++;
totalNumValues++;
totalSum = totalSum + value;
}
scanner.close();
System.out.println(salesData);
}
回答by lazyprogrammer
As @Justin Jasmann said, you have comma separated values, so technically they are more than just doublevalues, why not read them as String and then parse them using Double.parseDouble(String s)after you have your comma separatad value by using string.split(",");on every line.
正如@Justin Jasmann 所说，你有逗号分隔的值，所以从技术上讲，它们不仅仅是double值，为什么不将它们作为字符串读取，然后Double.parseDouble(String s)在你拥有逗号分隔值后使用string.split(",");在每一行上解析它们。
回答by Dark Knight
This is what you are looking for,
这就是你要找的
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.text.NumberFormat;
import java.text.ParseException;
import java.text.ParsePosition;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
public class FileRead {
public static void main(String args[])
{
try{
// Open the file that is the first
FileInputStream fstream = new FileInputStream("textfile.txt");
// Use DataInputStream to read binary NOT text.
BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
String strLine;
List<Double> saleNumbers= new ArrayList<Double>();
//Read File Line By Line
while ((strLine = br.readLine()) != null) {
// Add number from file to list
saleNumbers.add( parseDecimal(strLine));
}
//Close the input stream
in.close();
System.out.println(saleNumbers);
}catch (Exception e){
e.printStackTrace();
}
}
public static double parseDecimal(String input) throws NullPointerException, ParseException{
if(input == null){
throw new NullPointerException();
}
input = input.trim();
NumberFormat numberFormat = NumberFormat.getNumberInstance(Locale.US);
ParsePosition parsePosition = new ParsePosition(0);
Number number = numberFormat.parse(input, parsePosition);
if(parsePosition.getIndex() != input.length()){
throw new ParseException("Invalid input", parsePosition.getIndex());
}
return number.doubleValue();
}
}
回答by Esteban Filardi
I'd do something like this:
我会做这样的事情：
Scanner salesDataFile = new Scanner(new File("SalesData.txt"));
ArrayList<ArrayList< double > > salesData = new ArrayList<>();
while(salesDataFile.hasNextLine() )
{
String stringOfNumbers[] = salesDataFile.nextLine().split(",");
ArrayList< double > aux = new ArrayList<>( stringOfNumbers.length );
for( int i = 0; i < stringOfNumbers.length; ++i )
aux.get(i) = Double.parseDouble( stringOfNumbers[i] );
//... Perform your row calculations ...
salesData.add( aux );
}
salesDataFile.close();
System.out.println(salesData);
