Java. BufferWriter

Question

I'm new in java and currently learning how to read a file, do the work, and write the result to a file. My code can run with error free but I don't know why the output file can not print out anything from the consoles(it must print the last word of each line). Can anyone point me out how I can fix to make it work? Thank you so much. Here is my code.

import javax.swing.JButton;
import javax.swing.JFileChooser;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
public class ReadingWriting {
    private static BufferedReader reader;
    private static BufferedWriter writer;
    private static String currentLine;
    private static String result;


public static void main(String[] arg) {
    File inputFile=null;
    JButton open= new JButton();
    JFileChooser jfc = new JFileChooser();
    jfc.setCurrentDirectory(new java.io.File("."));
    jfc.setDialogTitle("ReadingWriting");
     if (jfc.showOpenDialog(open) == JFileChooser.APPROVE_OPTION){  
            inputFile = jfc.getSelectedFile();

            try {
            reader = new BufferedReader(new FileReader(inputFile));


            }catch (FileNotFoundException e){
            System.out.println("The file was not found");
            System.exit(0);
            }
     }
     try {
            Scanner input = new Scanner(inputFile);

            while ((currentLine = reader.readLine()) != null){

            currentLine = currentLine.trim();
            String[] wordList = currentLine.split("\\s+");
            String result =wordList[wordList.length-1];
            System.out.println(result+"");
            }

            input.close();
            reader.close();
            }catch (IOException e2){
            System.out.println("The file was not found");
            System.exit(0);
           }

     try{
            File outFile = new File("src/result.txt");
        writer= new BufferedWriter(new FileWriter(outFile));
        writer.write(result+"");
        writer.close();
        } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        }  

}        
}

Input file(hello.txt):

hello world

he is a good boy

345 123 46 765

output file(result.txt):

world

boy

765

My currently result.txt file :

null

Answer 1

There are a few issues with your code..

1. You createdresult twice (one class variable & one local variable)

   private static String result;
   ...
   String result =wordList[wordList.length-1];
   

Just like what EJP mentioned. Your local variable of String result =wordList[wordList.length-1]; actually shadows the class variable result. Hence, once you leave the scope of your while loop, the data is actually lost.

Outside the while loop, you are accessing the class variable resullt which is still empty.

---

2. Currently your while loop will only store the last word of the last sentence from your textfile.

You may write the result while you are reading it:

while ((currentLine = reader.readLine()) != null){
    currentLine = currentLine.trim();
    String[] wordList = currentLine.split("\\s+");
    String result =wordList[wordList.length-1];
    writer.write(result);    //write to file straight
}

Alternatively, you can save the last word of all sentences first, then perform the writing separately. This was also mentioned by user Tima:

ArrayList<String> resultList = new ArrayList<String>();
...

while ((currentLine = reader.readLine()) != null){
    currentLine = currentLine.trim();
    String[] wordList = currentLine.split("\\s+");
    resultList.add(wordList[wordList.length-1]);    //add to a list
}

...

//Perform your writing 
for(String s : resultList)
    writer.write(s);

Answer 2

You have created a result as temporary variable here.

String[] wordList = currentLine.split("\\s+");
String result = wordList[wordList.length - 1];
System.out.println(result + "");

You have to store all the read lines either in array then you write it later to another file.

Or

you can read line from one file and then write line in another file just after that.