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merge file and delete the old file

I have been trying to merge two files into new file and below code does it job. But after the merge i want to delete the old files. The code I am using to delete files just delete 1 file (file2) not the both of them.
public static void Filemerger() throws IOException
{
String resultPath = System.getProperty("java.io.tmpdir");
File result = new File(resultPath+"//NewFolder", "//file3.txt");
// PrintWriter object for file3.txt
PrintWriter pw = new PrintWriter(result);
// BufferedReader object for file1.txt
BufferedReader br = new BufferedReader(new FileReader(resultPath+"file1.txt"));
String line = br.readLine();
// loop to copy each line of
// file1.txt to file3.txt
while (line != null)
{
pw.println(line);
line = br.readLine();
}
pw.flush();
br = new BufferedReader(new FileReader(resultPath+"file2.txt"));
line = br.readLine();
// loop to copy each line of
// file2.txt to file3.txt
while(line != null)
{
pw.println(line);
line = br.readLine();
}
pw.flush();
// closing resources
br.close();
pw.close();
File dir = new File(resultPath);
FileFilter fileFilter1 = new WildcardFileFilter(new String[] {"file1.txt", "file2.txt"}, IOCase.SENSITIVE);
File[] fileList1 = dir.listFiles(fileFilter1);
for (int i = 0; i < fileList1.length; i++) {
if (fileList1[i].isFile()) {
File file1 = fileList1[i].getAbsoluteFile();
file1.delete();
}
}
}
I also try this code to delete the file1 as above code delete the file2:
Path fileToDeletePath = Paths.get(resultPath+"file1.txt");
Files.delete(fileToDeletePath);
but it throws an exception that Exception in thread "main" java.nio.file.FileSystemException: C:\Users\haya\AppData\Local\Temp\file1: The process cannot access the file because it is being used by another process.

Closing the streams as suggested in the comments will fix. However you are writing a lot of code which is hard to debug / fix later. Instead simplify to NIO calls and add try with resources handling to auto-close everything on the way:
String tmp = System.getProperty("java.io.tmpdir");
Path result = Path.of(tmp, "NewFolder", "file3.txt");
Path file1 = Path.of(tmp,"file1.txt");
Path file2 = Path.of(tmp,"file2.txt");
try(OutputStream output = Files.newOutputStream(result)) {
try(InputStream input = Files.newInputStream(file1)) {
input.transferTo(output);
}
try(InputStream input = Files.newInputStream(file2)) {
input.transferTo(output);
}
}
Files.deleteIfExists(file1);
Files.deleteIfExists(file2);

Find and replace in Java using regular expression without changing file format

I've a code which replaces 10:A to 12:A in a text file called sample.txt. Also, the code I've now is changing the file format, which shouldn't. Can someone please let me know how to do the same using regular expression in Java which doesn't change the file format? File has original format as below 10:A 14:Saxws But after executing the code it outputs as 10:A 14:Saxws.
import java.io.*;
import java.util.*;
public class FileReplace
{
List<String> lines = new ArrayList<String>();
String line = null;
public void doIt()
{
try
{
File f1 = new File("sample.txt");
FileReader fr = new FileReader(f1);
BufferedReader br = new BufferedReader(fr);
while ((line = br.readLine()) != null)
{
if (line.contains("10:A"))
line = line.replaceAll("10:A", "12:A") + System.lineSeparator();
lines.add(line);
}
fr.close();
br.close();
FileWriter fw = new FileWriter(f1);
BufferedWriter out = new BufferedWriter(fw);
for(String s : lines)
out.write(s);
out.flush();
out.close();
}
catch (Exception ex)
{
ex.printStackTrace();
}
}
public static void main(String[] args)
{
FileReplace fr = new FileReplace();
fr.doIt();
}
}

It looks like your OS or editor is not able to print correctly line separators generated by System.lineSeparator(). In that case consider
reading content of entire file to string (including original line separators), - then replacing part which you are interested in
and writing replaced string back to your file
You can do it using this code:
Path file = Paths.get("sample.txt");
//read all bytes from file (they will include bytes representing used line separtors)
byte[] bytesFromFile = Files.readAllBytes(file);
//convert themm to string
String textFromFile = new String(bytesFromFile, StandardCharsets.UTF_8);//use proper charset
//replace what you need (line separators will stay the same)
textFromFile = textFromFile.replaceAll("10:A", "12:A");
//write back data to file
Files.write(file, textFromFile.getBytes(StandardCharsets.UTF_8), StandardOpenOption.CREATE);

Writing with a PrintWriter to a file doesn't come out right

public static void doubleSpace(String fileName) {
try {
FileReader reader = new FileReader(fileName);
Scanner in = new Scanner(reader);
String outputFileName = fileName.charAt(0) + ".ds";
PrintWriter pOut = new PrintWriter(outputFileName);
// Opening of files for input and output
while (in.hasNextLine()) {
String line = in.nextLine();
pOut.println(line + "\n");
pOut.print("\n");
// System.out.println(line + "\n"); //Test
}
pOut.close(); // Close the files if they have been opened.
} catch (Exception e) {
}
}
So basically my input file contains
a
b
c
and my output file should look like
a
b
c
However, my output file always contains only abc.
Any help would be much appreciated!

Use a BufferedWriter. It has a .newLine() method. This method will use the platform's default line separator.
And use a BufferedReader. It has a .readLine() method.
Example:
// NOTE: you should really be using UTF-8
final Charset charset = Charset.defaultCharset();
final Path src = Paths.get(filename);
final Path dst = Paths.get(filename + ".ds");
String line;
try (
final BufferedReader reader = Files.newBufferedReader(src, charset);
final BufferedWriter writer = Files.newBufferedWriter(dst, charset);
) {
while ((line = reader.readLine()) != null) {
writer.write(line);
writer.newLine();
writer.newLine();
}
}

You are likely useing the wrong character(s) for new line for your plattform. Use
System.getProperty("line.separator");
to get the right value.

Java code to remove initial lines of a file executing very slow

I have written java code to remove initial characters from a file with 200k records , the file is removing the initial characters but its reading the file line by line and removing the characters .The program is executing very slow . Any tweaks could be made to below code to execute it faster ?
The program is executing and writing the output to a file , but its very slow
import java.io.*;
import java.util.Scanner;
public class truncate {
public static void main(String [] args) {
// The name of the file to open.
String inputfile = "C:\\Program Files\\eclipse\\twfiles.txt";
String outputfile = "C:\\Program Files\\eclipse\\rename.txt";
// This will reference one line at a time
String line = "";
int number_of_char_to_erased =19;
try {
// FileReader reads text files in the default encoding.
FileReader fileReader =
new FileReader(inputfile);
// Always wrap FileReader in BufferedReader.
BufferedReader bufferedReader =
new BufferedReader(fileReader);
while((line = bufferedReader.readLine()) != null) {
System.out.println(line);
File input = new File(inputfile);
Scanner scan = new Scanner(input);
File output = new File(outputfile);
PrintStream print = new PrintStream(output);
while (scan.hasNext()) {
line = scan.nextLine();
line = line.substring(number_of_char_to_erased);
print.println(line);
}
scan.close();
print.close();
}
// Always close files.
bufferedReader.close();
}
catch(FileNotFoundException ex) {
System.out.println(
"Unable to open file '" +
inputfile + "'");
}
catch(IOException ex) {
System.out.println(
"Error reading file '"
+ inputfile + "'");
// Or we could just do this:
// ex.printStackTrace();
}
}
}

What appears to be the issue here is that you just created a buffered reader to read the file. Then, it reads the first line of the file. Then, you create a Scanner to read ALL the lines in the file, omitting certain characters. Then your BufferedReader reads the next line in the file. And the process repeats itself. So all you have to do is this:
File output = new File(outputfile);
PrintStream print = new PrintStream(output);
while((line = bufferedReader.readLine()) != null) {
print.println(line.substring(number_of_char_to_erased);
}
print.close();
This should much faster. Basically, since you've already allocated line to the read line from the file, you can simply print out that line, minus the number of chars, to the output file. The entire for loop with scanner was entirely unnecessary, and closing and opening the print stream for each line was also unnecessary.
EDIT: Removed the println statement since it would slow it down a bit.

Try this (Scanner and Println removed, output file refactored outside the loop):
import java.io.*;
public class truncate {
public static void main(String [] args) {
// The name of the file to open.
String inputfile = "C:\\Program Files\\eclipse\\twfiles.txt";
String outputfile = "C:\\Program Files\\eclipse\\rename.txt";
// This will reference one line at a time
String line = "";
int number_of_char_to_erased =19;
try {
// FileReader reads text files in the default encoding.
FileReader fileReader = new FileReader(inputfile);
// Always wrap FileReader in BufferedReader.
BufferedReader bufferedReader = new BufferedReader(fileReader);
File output = new File(outputfile);
PrintStream print = new PrintStream(output);
while((line = bufferedReader.readLine()) != null) {
String trimmedLine = line.substring(number_of_char_to_erased);
print.println(trimmedLine);
}
// Always close files.
bufferedReader.close();
print.close();
}
catch(FileNotFoundException ex) {
System.out.println(
"Unable to open file '" +
inputfile + "'");
}
catch(IOException ex) {
System.out.println(
"Error reading file '"
+ inputfile + "'");
// Or we could just do this:
// ex.printStackTrace();
}
}
}

How can I overwrite lines from text file to specific lines in another file instead of appending them

public class AddSingleInstance {
public void addinstances(String txtpath,String arffpath) throws IOException {
BufferedReader reader = new BufferedReader(new FileReader("C:\\src\\text.txt"));
FileWriter fw = new FileWriter("C:\\src\\" + test.txt,true);
StringBuilder sb = new StringBuilder();
//String toWrite = "";
String line = null;
while ((line = reader.readLine())!= null){
// toWrite += line;
sb.append(line);
sb.append("\n");
}
reader.close();
fw.write(sb.toString());
fw.flush();
fw.close();
}
}
my code is working on append lines from text file(A) to specific lines in another file(B), like
I
AM
......
(above lines are fixed, cannot be overwriting)
student(New string was added from text file)
now(New string...)
How can I overwrite those lines into file(B) instead of appending them on B?

You can use java.io.RandomAccessFile to access file(B) and write to it at the desired location.