Read Double From a .txt File into an Array List

So we have this program where we have to read double values from a text file into a double ArrayList and make certain calculations.

example of the text file:

Note: there's space between the date and the double values

5/05/1998 4.4

1/01/1999 -4.123


the problem is that i'm getting is as below:

"NumberFormatException for input string: 1/2/1950 0.0258" error.

Here's my code:

public static void value() throws java.io.IOException
try
BufferedReader br = new BufferedReader(new FileReader(new File("SP500-Weekly.txt")));
ArrayList<Double>list = new ArrayList<Double>();
String line;
while((line=br.readLine())!=null)
String r = line.split(" ");
for(int i=0; i<r.length; i++)
double val = Double.parseDouble(r[i]);
list.add(val);

br.close();
System.out.println(list.size());

catch(IOException io)
System.out.println("error");




3 Answers
3

Seems like you just need the double value present on each line and want to add it into a List<Double>. Based off of your input, second value is always your double value, but you are trying to parse first value as well which is a date and Double.parseDouble() cannot parse characters that comes in a date such as /, thus you ran into exception. If the double value is what you need then do it simply as :

double

List<Double>

Double.parseDouble()

/

try
BufferedReader br = new BufferedReader( new FileReader( new File( "SP500-Weekly.txt"" ) ) );
List<Double> list = new ArrayList<Double>();
String line;

while ( ( line = br.readLine( ) ) != null )

String r = line.split( "\s+" );
list.add( Double.parseDouble( r[ 1 ] ) );

br.close( );
System.out.println( list.size( ) );
catch ( IOException io )
e.printStackTrace( );



You can then play around with list variable as your wish.

list

Also if you want to be more specific and check if it's actually number/double for second value then I'd do following to add a regex which will make sure that the second value is number (with or without - sign) as below:

-

while ( ( line = br.readLine( ) ) != null )
String r = line.split( "\s+" );
for ( String string: r )
if ( string.matches( "^-?[0-9]?.?[0-9]+" ) )
list.add( Double.parseDouble( r[ 1 ] ) );





A very simple and up to date implementation of this using java.nio and pure Java 8 would the following.

java.nio

private static List<Double> readDoubles(final String fileName)
try (Stream<String> stream = Files.lines(Paths.get(fileName)))
return stream.map(s -> s.split("\s+")[1])
.map(Double::parseDouble)
.collect(Collectors.toList());
catch (IOException e)
e.printStackTrace();

return Collections.emptyList();



Implementation also takes the liberty of using try-with-resources to auto manager the various resources.

try-with-resources

CORRECTCODE:

import java.util.List;
class Sample extends SimulateMarket
public static void value()
try
BufferedReader br = new BufferedReader(new FileReader(new File("SP500-Weekly.txt")));
List<Double> list = new ArrayList<Double>();
String line;
while((line=br.readLine())!=null)
String r = line.split("\s+");
list.add(Double.parseDouble(r[1]));
br.close();
Random rand = new Random();
int randomIndex = rand.nextInt(list.size());
System.out.println(list.get(randomIndex));

catch(IOException io)
System.out.println("error");




ArrayList<Double>list = new ArrayList<Double>();

List<Double> list = new ArrayList<Double>();

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