I don't know how to handle java strings and ArrayList.

Hi, nice to meet you.I have been studying java for about 3 months.
The text file printed with the following code will never be the ideal value.

Specifically, two text files are taken for input.Each text file is formatted like a comma-separated CSV file, for example,

1,2,3,4,5
2,,5

1,3,5,7,9

It looks like .Some lines are empty or empty.

What I want to do with this code is to add the two text files that match each other and output them to a new text file.Apart from the previous example,

1,1,1,1
2,2,2,2
3,3,3
4,4
5

When prepared, the output is as follows:

2,3,4,5,6
4,2,7,2
3,3,3
5,7,5,7,9
5

What doesn't work is that after the second line, the calculation doesn't work, the empty line doesn't work, and I don't know if the output method is correct. I'm sure there are other things that don't work, but please let me know.

Also, I think there is definitely a good alternative, so I would appreciate it if you could suggest it as an alternative solution.

Thank you for your cooperation.

import java.io.*;
import java.util.*;

public classNum_Array{
    public static void main(String[]args) {
        ArrayList<ArrayList<Integer>>list=new ArrayList<ArrayList<Integer>(); 
        ArrayList<Integer>row;

        try{
            FileReader fr=new FileReader("1041.txt");
            FileReader fr2 = new FileReader ("1042.txt");
            BufferedReader br = new BufferedReader (fr);
            BufferedReader br2 = new BufferedReader (fr2);
            File f = new File ("output104.txt");
            FileWriter filewriter = new FileWriter(f);
            String str1 = null;
            str1 = br.readLine();
            String str2 = null;
            str2 = br2.readLine();
            
            while(str1!=null&str2!=null){
                int num = 0;
                int add_num = 0;
 
                String [ ] nstr1 = str1.split(", ");
                String [ ] nstr2 = str2.split(", ");
                row=new ArrayList<Integer>();
           
                for(inti=0;i<nstr1.length||i<nstr2.length;i++){
                    if(i<nstr1.length&i<nstr2.length){
                        if(nstr1[i].equals(""){
                            nstr1[i] = "0";
                        }
                        if(nstr2[i].equals(""){
                            nstr2[i] = "0";
                        }
                        // System.out.println(nstr2[i]);
                        num = Integer.valueOf(nstr1[i]);
                        add_num = Integer.valueOf(nstr2[i]);
                        num+=add_num;
                        row.add(num);
                    }
                
                    if(i>=nstr1.length){
                        row.add(Integer.valueOf(nstr2[i]));
                    } else if(i>=nstr2.length) {
                        row.add(Integer.valueOf(nstr1[i]));
                    }
                }
                list.add(row);
                str1 = br.readLine();
                str2 = br.readLine();
            }
            for(inti=0;i<list.size();i++){
                for(int j=0;j<list.get(i).size();j++){
                    filewriter.write(String.valueOf(list.get(i).get(j)));
                    if(j!=list.get(i).size()-1){
                        filewriter.write(", ");
                    } else {
                        filewriter.write("\n");
                    }
                }
            }
            br.close();
            br2.close();
            filewriter.close();
            fr.close();
            fr2.close();
        }catch(IOExceptione){
            System.out.println(e.getMessage());
        }
    }
}

java text-file

2022-09-30 19:26

1 Answers

There are two problems.

The first is to confuse the two BufferedReaders when reading the next line.

str1=br.readLine();
str2 = br.readLine();

The second line of the quote above should use br2.

The second condition is to finish reading the file.

while(str1!=null&str2!=null){

The longer line file is not processed until the end because either end will exit the loop.

Will both continue until null (where null is set to a dummy)?

while(str1!=null||str2!=null){
    // ...
    String [ ] nstr1 = str1! = null?str1.split(", "): new String [0];
    String [ ] nstr2 = str2! = null?str2.split(", "): new String [0];

Also, this is not a direct problem, but

if(i<nstr1.length&i<nstr2.length){
    // ...
}

if(i>=nstr1.length){
    // ...
} else if(i>=nstr2.length) {
    // ...
}

The conditions of are in the same column, so

if(i<nstr1.length&i<nstr2.length){
    // ...
} else if(i>=nstr1.length){
    // ...
} else if(i>=nstr2.length){
    // ...
}

I think it would be better if

"As for ""another method is good"", it is difficult to answer because of the wide range of questions, but regarding this question,

Two file operations often overlap, so methodize to improve visibility
The line is a little special, so you can use it a little simpler from the outside by classifying it.

I think there are things like that.
If you class the lines, for example, I think it will look like this.

2022-09-30 19:26

If you have any answers or tips

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