使用lambdas将字符串arraylist转换为double arraylist

Question

I need some help regarding converting string array list to double array list using java lambdas upto now I had tried these.

List<Double> Doublevalues1 = valueItemsToList.stream().mapToDouble(Double::parseDouble).boxed().collect(Collectors.toList());

and this in general

 for(int j = 0; j< valueItemsToList.size();j++)
    {
         Doublevalues1.add(Double.parseDouble(valueItemsToList.get(j)));
         //Doublevalues.add(Double.valueOf(valueItemsToList.get(j)));
    }

can anyone tell me where I gone wrong This is not duplicate answer I tried all possibilites I had gone through the net but none of them gave me correct answer glad if you could help. this is my complete code

 public class Stock {
public static void main(String[] args) {
    // TODO code application logic here
    String buff[] = new String[4988];
    int i = 0;
    File file = new File("C:\\Users\\admin\\Desktop\\data.csv");
    try{
        FileInputStream fis = new FileInputStream(file);
        BufferedReader dis = new BufferedReader(new InputStreamReader(fis));
        String s;
        while ((s = dis.readLine()) != null) {
           // System.out.println(s);
            buff[i] = s;
            i++;
          // String[] s1 = s.split(",");
        }
    }
    catch(Exception e)
    {
         System.out.println("error happend at block try at fileinput");
    }
     //converting array string to arraylist
     List<String> valueItemsToList = Arrays.asList(buff);
     //valueItemsToList.forEach(System.out::println);
     List<Double> Doublevalues1 = new ArrayList<Double>();// valueItemsToList.stream().mapToDouble(Double::parseDouble).boxed().collect(Collectors.toList());
    for(int j = 0; j< valueItemsToList.size();j++)
    {
         Doublevalues1.add(Double.parseDouble(valueItemsToList.get(j)));
         //Doublevalues.add(Double.valueOf(valueItemsToList.get(j)));
    }
     Doublevalues1.forEach(System.out::println);
}
}

error: its little bit clumsy its here complete

Exception in thread "main" java.lang.NullPointerException at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1838) at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.lang.Double.parseDouble(Double.java:538) at stock.Stock.main(Stock.java:53) C:\\Users\\admin\\AppData\\Local\\NetBeans\\Cache\\8.1\\executor-snippets\\run.xml:53: Java returned: 1 BUILD FAILED (total time: 2 seconds)

Answer 1

Agree with @bayou.io, either use ArrayList<String> in place of buff[]

(because if the number of lines in your input file are less 4988 then you will get NullPointerExcetion and if you have more lines then you will get ArrayIndexOutOfBoundsException)

or place null check before String to Double conversion eg

for(int j = 0; j< valueItemsToList.size();j++)
{
    if(valueItemsToList.get(j) != null){ // NULL Check
        Doublevalues1.add(Double.parseDouble(valueItemsToList.get(j)));
        //Doublevalues.add(Double.valueOf(valueItemsToList.get(j)));
    }
}

Answer 2

List<String> valueItemsToList = Arrays.asList(buff);
     //valueItemsToList.forEach(System.out::println);
     List<Double> Doublevalues1 = new ArrayList<Double>();// valueItemsToList.stream().mapToDouble(Double::parseDouble).boxed().collect(Collectors.toList());
    for(int j = 0; j< valueItemsToList.size();j++)
    {
         Doublevalues1.add(Double.parseDouble(valueItemsToList.get(j)));
         //Doublevalues.add(Double.valueOf(valueItemsToList.get(j)));

    }
     Doublevalues1.forEach(System.out::println);

solved thanks for your posts