如何比较文本文件的每一行？ java的

Question

I have a text file with content like, with 792 lines:

der 17788648
und 14355959
die 10939606
Die 10480597

Now I want to compare if "Die" and "die" are equal in lowercase. So if two Strings in lowerCase are equal, copy the word into a new text file in lowerCase and sum the values.

Expected output:

der 17788648
und 14355959
die 114420203

I have that so far:

    try {
        BufferedReader bk = null;
        BufferedWriter bw = null;

        bk = new BufferedReader(new FileReader("outagain.txt"));
        bw = new BufferedWriter(new FileWriter("outagain5.txt"));

        List<String> list = new ArrayList<>();
        String s = "";
        while (s != null) {
            s = bk.readLine();
            list.add(s);
        }


        for (int k = 0; k < 793; k++) {
            String u = bk.readLine();
            if (list.contains(u.toLowerCase())) {

                //sum values?

            } else {
                bw.write(u + "\n");
            }
        }

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

    } catch (Exception e) {
        System.out.println("Exception caught : " + e);
    }

Answer 1

Instead of list.add(s); , use list.add(s.toLowerCase()); . Right now your code is comparing lines of indeterminate case to lower-cased lines.

Answer 2

With Java 8, the best approach to standard problems like reading files, comparing, grouping, collecting is to use the streams api, since it is much more concise to do that in that way. At least when the files is only a few KB, then there will be no problems with that. Something like:

Map<String, Integer> nameSumMap = Files.lines(Paths.get("test.txt"))
            .map(x -> x.split(" "))
            .collect(Collectors.groupingBy(x -> x[0].toLowerCase(),
                    Collectors.summingInt(x -> Integer.parseInt(x[1]))
            ));

First, you can read the file with Files.lines() , which returns a Stream<String> , than you can split the strings into a Stream<String[]> , finally you can use the groupingBy() and summingInt() functions to group by the first element of the array and sum by the second one.

If you don't want to use the stream API, you can also create a HashMap und do your summing manually in the loop.

Answer 3

The String class has an equalIgnoreCase method which you can use to compare two strings irrespective of case. so:

String var1 = "Die";
String var2 = "die";

System.out.println(var1.equalsIgnoreCase(var2));

Would print TRUE.

Answer 4

If I got your question right, you want to know how you can get the prefix from the file, compare it, get the value behind it and sum them up for each prefix. Is that about right?

You could use regular expressions to get the prefixes and values seperately. Then you can sum up all values with the same prefix and write them to the file for each one.

If you are not familiar with regular expressions, this links could help you:

Regex on tutorialpoint.com

Regex on vogella.com

For additional tutorials just scan google for "java regex" or similar tags.

If you do not want to differ between upper- and lowercase strings, just convert them all to lower/upper before comparing them as @spork explained already.

Answer 5

Use a HashMap to keep track of the unique fields. Before you do a put, do a get to see if the value is already there. If it is, sum the old value with the new one and put it in again (this replaces the old line having same key)

package com.foundations.framework.concurrency;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;

public class FileSummarizer {

  public static void main(String[] args) {
    HashMap<String, Long> rows = new HashMap<String, Long>();
    String line = "";
    BufferedReader reader = null;
    try {
      reader = new BufferedReader(new FileReader("data.txt"));
      while ((line = reader.readLine()) != null) {
        String[] tokens = line.split(" ");
        String key = tokens[0].toLowerCase();
        Long current = Long.parseLong(tokens[1]);

        Long previous = rows.get(key);
        if(previous != null){
          current += previous;
        }
        rows.put(key, current);
      }
    }
    catch (IOException e) {
      e.printStackTrace();
    }
    finally {
      try {
        reader.close();
        Iterator<String> iterator = rows.keySet().iterator();
        while (iterator.hasNext()) {
          String key = iterator.next().toString();
          String value = rows.get(key).toString();

          System.out.println(key + " " + value);
        }
      }
      catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}