replace a line to above line for every two lines java

Question

I have a text file like this:

Emma,F,20355
Olivia,F,19553
Sophia,F,17327
Ava,F,16286
Isabella,F,15504
Mia,F,14820
Abigail,F,12311
Emily,F,11727

I am trying to remove words after , and also put two lines in one line for every two lines. For example:

Emma Olivia
Sophia Ava
Isabella Mia
Abigail Emily

The program can do the first part, but I don't know how the program can do the second part. I can split the words and numbers after first ,, but I got stuck how I can can arrange lines.

Here is the code:

BufferedReader reader = new BufferedReader(new FileReader(inputFile));
BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));
String currentLine;
String[] a;
String res;
while ((currentLine = reader.readLine()) != null) {
    a = currentLine.split(",");
    res = a[0] + "\n";
    writer.write(res);
}
writer.close();
reader.close();

I think I need to create a for loop inside while loop, but I am not sure what to write to count even or odd lines.

Refer this http://stackoverflow.com/questions/455695/what-is-the-best-way-to-read-a-text-file-two-lines-at-a-time-in-java — Unknown, Jun 17 '16 at 20:15

score 2 · Answer 1 · edited Jun 17 '16 at 21:02

2

Change to to something like this :

int count = 1;
while ((currentLine = reader.readLine()) != null) {
    a = currentLine.split(",");
    res = a[0] + count % 2 == 0 ? "\n" : " ";
    count++;
    writer.write(res);
}

edited Jun 17 '16 at 21:02

4castle

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answered Jun 17 '16 at 20:18

Arpit Ratan

2,976
1
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20

4castle · Answer 2 · 2016-06-17T21:07:34.797

2

try (
    BufferedReader reader = new BufferedReader(new FileReader(inputFile));
    BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile))
) {
    while (true) {
        String line1 = reader.readLine();
        if (line1 == null) { 
            break;
        }
        writer.write(line1.split(",", 2)[0]);

        String line2 = reader.readLine();
        if (line2 == null) {
            writer.newLine();
            break;
        }
        writer.write(" " + line2.split(",", 2)[0]);
        writer.newLine();
    }
}

edited Jun 17 '16 at 21:07

answered Jun 17 '16 at 20:19

4castle

32,613
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Wrong. Exception will be thrown for incorrect input. – questioner and answerer Jun 17 '16 at 20:25
@questionerandanswerer What exception? Like `null`? – 4castle Jun 17 '16 at 20:27
You read line inside, so if number of lines is odd, exception will be thrown when you try to read new line, because there may be no line. – questioner and answerer Jun 17 '16 at 20:27
@questionerandanswerer Fixed now. It's also using `try-with-resources` as Elliott recommended. – 4castle Jun 17 '16 at 20:34
If it matters, this would still give inconsistent file endings (newline at end of last line) for odd vs even row count since the writer.newLine() will be skipped for odd rows. – Jeff Neet Jun 17 '16 at 20:49
1

@JeffNeet I'm not even sure if an odd number will happen in the first place (the OP will need to clarify), but I will edit. – 4castle Jun 17 '16 at 20:53

score 1 · Answer 3 · edited Jun 17 '16 at 21:03

1

int newLine = 1;
while ((currentLine = reader.readLine()) != null) {
    a = currentLine.split(",");
    if (newLine % 2 == 0)
        res += a[0] + "\n";
    else
        res += a[0] + " ";
    newLine++;
}
writer.write(res);

edited Jun 17 '16 at 21:03

4castle

32,613
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answered Jun 17 '16 at 20:18

ramiz samol

31
7

Storing an entire file in a string isn't a very good idea. It's better to write to the other file as you iterate. – 4castle Jun 17 '16 at 21:09

score 1 · Answer 4 · edited Jun 17 '16 at 21:04

1

Try reading two lines in at the same time if there is a second line left in the reader.

Something like this:

BufferedReader reader = new BufferedReader(new FileReader(inputFile));
BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));
String currentLine;
String[] a;
String[] b;
String res;
while ((currentLine = reader.readLine()) != null) {
    a = currentLine.split(",");
    if (reader.hasNext()) {
        b = reader.readLine().split(",");
        res = a[0] + " " + b[0] + "\n";
    } else {
        res = a[0]+"\n";
    }
    writer.write(res);
}
writer.close();
reader.close();

edited Jun 17 '16 at 21:04

4castle

32,613
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answered Jun 17 '16 at 20:23

Jeff Neet

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1

While this looks *okay*, I would prefer [`try-with-resources`](http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html) to the two explicit `close` calls. – Elliott Frisch Jun 17 '16 at 20:25
@ElliottFrisch That's a good idea. Is my answer doing that right? – 4castle Jun 17 '16 at 20:38
That's a fair point. I simply copied the code provided by the OP and modified the parts directly relevant to their question. However, instantiating the BufferedReader within a try-with-resources block (assuming Java 7+) is definitely a safer way to go. – Jeff Neet Jun 17 '16 at 20:41

score 0 · Answer 5 · edited Jun 17 '16 at 21:06

As mentioned above, read in two lines at a time. Combine them, then split based on the delimiter (comma) - Should then be easy to write out new format to a text file (Maybe pop the results in a list, then iterate over the list to write it out.

This is not a complete solution, but should be enough for you to get the idea.

// Read two lines at a time
String currentLine = reader.readLine(); //Emma,F,20355
String nextLine = reader.readLine();    //Olivia,F,19553

String combinedLine = currentLine + "," + nextLine;

// split into separate elements
String[] elements = combinedLine.split(",");

List<String> newLines = new ArrayList<>();
newLines.add(elements[0] + " " + elements[3]);

for (final String line : newLines) {
    // write to file
    writer.write(res);
}

replace a line to above line for every two lines java

5 Answers5