Java BufferReader 到按行存储的数组

Question

Given a list of polynoms I need to store them on different arrays depending on the row. Example:

5 -4 2 0 -2 3 0 3 -17 int[] a = {-17, 3, 0, 3, -2, 0, 2, -4, 5}

4 -2 0 1 int[] b = {1, 0, -2, 4}

First line I need to put on the array a[], and the second one on array b[] Tried something like this:

File file=new File("Pol.txt");
BufferedReader b=new BufferedReader(new InputStreamReader(new FileInputStream(file)));
Pattern delimiters=Pattern.compile(System.getProperty("line.separator")+"|\\s");
String line=b.readLine();

Answer 1

First, you will want to make sure that any file reading objects are always properly cleaned up. A try-with-resources block is your best bet, or otherwise a try finally block.

try(BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(
        new FileInputStream(file))) {
    //code using bufferedReader goes here.
}

You should not need to use the Pattern class here. It's a simple case of reading a line and using the String.split method. eg

String line = bufferedReader.readLine();
//if (line == null) throw an exception
String[] splitLine = line.split("\\s+");

Now the splitLine variable will contain an array of Strings, which is each of the elements from the original line, as separated by spaces. The split method takes a String which is the regular expression representing the 'delimiter' of your values. For more information on regular expressions in Java, try this . The "\\\\s+" represents any whitespace character or characters These can be 'parsed' to int values using the Integer.parseInt method, like this:

int[] a = new int[splitLine.length];
for(int i = 1; i <= splitLine.length; i++) {
    int parsed = Integer.parseInt(splitLine[i]);
    a[splitLine.length - i] = parsed;
}

The parseInt method may throw a NumberFormatException , for example if you give it the String "Hello world" . You can either catch that or let it be thrown.