逐行读取Java

Question

I have a textfile which looks like this:

1 
2 3
4 5
6 7

I want to have 2 strings that are the values of same line. Example:

String s1 will be 2, String s2 will be 3

I tried like this:

    File file = new File("e:\\read.txt");
    if (file.exists()){
     FileReader fr = new FileReader(file);
     LineNumberReader ln = new LineNumberReader(fr);
        while (ln.getLineNumber() == 0){

            s=Integer.parseInt(ln.readLine());
         System.out.println(s);
        }
        DisjointSetLinkedList dsj=new DisjointSetLinkedList();
        while(ln.getLineNumber()>0)
        {

           String [] tokens = ln.readLine().split(" ");
           s1=tokens[0];
           System.out.println( s1);
        }

I have to make union between 2 strings, that are on the same line:

Answer 1

Change your second loop to :

    String line = null;
    while ((line = ln.readLine()) != null) {

        String[] tokens = line.split(" ");
        String s1 = tokens[0];
        String s2 = tokens[1];
        System.out.println("s1 = " + s1 + " s2 = " + s2);
    }

Otherwise you'll have NullPointerException when trying to access last line read with ln.readLine() .

You also don't need while loop to read first line, just read it once.

Answer 2

I think sth like that is easier:

    try {
        File file = new File("numbers.txt");
        FileReader fr = new FileReader(file);
        BufferedReader br = new BufferedReader(fr);
        String line;
        while ((line = br.readLine())!= null) {
            String[] tokens = line.split("\\s");
            System.out.println(Arrays.toString(tokens));
        }
    } catch (Exception e) {
        e.printStackTrace();
    }

Answer 3

if you have token[0] as the entire first row you can union like this

for(int i=2; i<token.length;i+2)
   System.out.println("UNION: "+Union(token[i-2], token[i]));