Develop Reference

How can I delete lines of data in textfile using java? eg. my textfile is data.txt

From read the line needed to be deleted by the user to delete it
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.Scanner;
public class Delete {
public static void main(String[] args) throws IOException {
File input = new File("data.txt");
FileReader fr = null;
Scanner ob = new Scanner(System.in);
// declare variable
String DeleteWord, str, newDeleteWord;
System.out.print("Enter word you want to delete: ");
DeleteWord = ob.nextLine();
newDeleteWord = (capitalize(DeleteWord));
try {
fr = new FileReader(input);
BufferedReader br = new BufferedReader(fr);
while ((str = br.readLine()) != null) {
if (str.contains(newDeleteWord)) {
System.out.println(str);
}
Scanner read = new Scanner(System.in);
int selection;
System.out.println("Confirm to delete his/her data?\n 1 for yes\n 2 for no");
selection = read.nextInt();
if (selection == 1)
if (str.contains(newDeleteWord)) {
str = "";
}
}
} finally {
fr.close();
}
}
public static String capitalize(String str1) {
if (str1 == null || str1.isEmpty()) {
return str1;
}
return str1.substring(0, 1).toUpperCase() + str1.substring(1);
}
}
How can I delete lines of data in textfile using java? eg. my textfile is data.txt

This is a possible solution:
File inputFile = new File("myFile.txt"); // File which we will read
File tempFile = new File("myTempFile.txt"); // The temporary file where we will write
BufferedReader reader = new BufferedReader(new FileReader(inputFile));
BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));
String lineToRemove = yourString; // here is your line to remove
String currentLine;
while((currentLine = reader.readLine()) != null) {
String trimmedLine = currentLine.trim(); // we trim it and remove unecessary spaces
if(trimmedLine.equals(lineToRemove)) continue; // If it is equal to our line to remove then do not write it to our file!
writer.write(currentLine + System.getProperty("line.separator"));
}
writer.close();
reader.close();
inputFile.delete(); // we delete the file that we have so that we have no conflicts
boolean successful = tempFile.renameTo(inputFile);
OR
Reading all the lines in a list and filtering this list.
The quickest way is through Apache Commons-IO ( or you can implement it yourself)
Apache Commons:
List<String> lines = FileUtils.readLines(file);
List<String> updatedLines = lines.stream().filter(s -> !s.contains(searchString)).collect(Collectors.toList());
FileUtils.writeLines(file, updatedLines, false);

java homework with word replacement

Hello can someone help me? The point of the homework is to read a file then create another file where it replaces all of the words "is" with "was", i have all this done but I am also not sopposed to replace words that have"is" in them, for example: "this, isthmus".
import java.io.*;
import java.util.*;
public class WordChange {
public static void main(String[]args) throws Exception {
FileReader fr = null;
FileWriter fw = null;
try
{
Scanner keyboard=new Scanner(System.in);
System.out.println("Enter the name of the text file: ");
String fileName=keyboard.nextLine();
File file = new File(fileName);
BufferedReader reader = new BufferedReader(new FileReader(file));
String line = "", oldtext = "";
while((line = reader.readLine()) != null)
{
oldtext += line + "\r\n";
}
reader.close();
String replacedtext=oldtext.replaceAll("is ","was ");
FileWriter writer = new FileWriter("output.txt");
writer.write(replacedtext);
writer.close();
}
catch (IOException ioe)
{
ioe.printStackTrace();
}
}
}

just a guess here but instead of
String replacedtext=oldtext.replaceAll("is ","was ");
would this work
String replacedtext=oldtext.replaceAll(" is "," was ");
Im just guessing let me know if it works

How to remove garbage values from csv file?

I have a CSV file with some data and it also has a lot of invalid data in it. How can I print only the valid data and leave rest of it?
My data is like this:-
1,Ron,1234,XYZ
2,Harry,214,SDA
3,Kent,1786,GHI
SAMNE:MANNS;ndndo
kdbg;obmgdf;brhj
I want to print only the first 3 lines and remove the last two invalid lines. I am doing this in Eclipse.

You can try something like this.
BufferedReader reader = new BufferedReader(new FileReader(new File("~/input.csv")));
String line;
while((line = reader.readLine())!= null){
try{
int sno = Integer.parseInt( line.split(",")[0]);
System.out.println("Valid "+ line);
//Continue doing more checks or other operations
}catch(NumberFormatException e){
//Skip invalid line
System.out.println("Invalid row "+ line);
}
}

You should check by regex if is valid, throw an exception is a bad idea.
BufferedReader reader = new BufferedReader(new FileReader(new File("~/input.csv")));
String line;
while((line = reader.readLine())!= null){
if(line.matches("(\\d+,\\w+,\\d+,\\w+)"){
print line;
}
}

Something like this:
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
public class JavaApplication1 {
public static void main(String[] args) throws FileNotFoundException, IOException {
try (BufferedReader reader = new BufferedReader(new FileReader("file.txt"))) {
StringBuilder sb = new StringBuilder();
String line = reader.readLine();
while (line != null) {
String[] part = line.split(",");
try {
Integer.parseInt(part[0]);
System.out.println(line);
} catch (NumberFormatException nfe) {
// This is not a valid line
}
line = reader.readLine();
}
}
}
}

How to print lines from a file that contain a specific word using java?

How to print lines from a file that contain a specific word using java ?
Want to create a simple utility that allows to find a word in a file and prints the complete line in which given word is present.
I have done this much to count the occurence but don't knoe hoe to print the line containing it...
import java.io.*;
public class SearchThe {
public static void main(String args[])
{
try
{
String stringSearch = "System";
BufferedReader bf = new BufferedReader(new FileReader("d:/sh/test.txt"));
int linecount = 0;
String line;
System.out.println("Searching for " + stringSearch + " in file...");
while (( line = bf.readLine()) != null)
{
linecount++;
int indexfound = line.indexOf(stringSearch);
if (indexfound > -1)
{
System.out.println("Word is at position " + indexfound + " on line " + linecount);
}
}
bf.close();
}
catch (IOException e)
{
System.out.println("IO Error Occurred: " + e.toString());
}
}
}

Suppose you are reading from a file named file1.txt Then you can use the following code to print all the lines which contains a specific word. And lets say you are searching for the word "foo".
import java.util.*;
import java.io.*;
public class Classname
{
public static void main(String args[])
{
File file =new File("file1.txt");
Scanner in = null;
try {
in = new Scanner(file);
while(in.hasNext())
{
String line=in.nextLine();
if(line.contains("foo"))
System.out.println(line);
}
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}}
Hope this code helps.

public static void grep(Reader inReader, String searchFor) throws IOException {
BufferedReader reader = null;
try {
reader = new BufferedReader(inReader);
String line;
while ((line = reader.readLine()) != null) {
if (line.contains(searchFor)) {
System.out.println(line);
}
}
} finally {
if (reader != null) {
reader.close();
}
}
}
Usage:
grep(new FileReader("file.txt"), "GrepMe");

Have a look at BufferedReader or Scanner for reading the file.
To check if a String contains a word use contains from the String-class.
If you show some effort I'm willing to help you out more.

you'll need to do something like this
public void readfile(){
try {
BufferedReader br;
String line;
InputStreamReader inputStreamReader = new InputStreamReader(new FileInputStream("file path"), "UTF-8");
br = new BufferedReader(inputStreamReader);
while ((line = br.readLine()) != null) {
if (line.contains("the thing I'm looking for")) {
//do something
}
//or do this
if(line.matches("some regular expression")){
//do something
}
}
// Done with the file
br.close();
br = null;
}
catch (Exception ex) {
ex.printStackTrace();
}
}

Writing the text from the back

As in the tittle , i want to write my text from back and enter to the text file . In first , i read the text from the text file , next i want to save it in text file , but writing by the end of. I don't have any ideas how to fix my code . My code read the text file , and write the text file , but in the same order , from beginning to ending.
Example how it must work:
input text:
aaaaa
bbbb
ccc
dd
f
output text:
f
dd
ccc
bbbb
aaaaa
My code:
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
public class Loading {
public static void main(String[] args) {
try {
BufferedReader br = new BufferedReader(new FileReader(
"file.txt.txt"));
String line, txt = "";
String[] splittedLine;
while ((line = br.readLine()) != null) {
txt += linia + "\n";
splittedLine = line.split(" ");
}
System.out.println(txt);
br.close();
BufferedWriter bw = new BufferedWriter(new FileWriter("file2"));
bw.write(txt);
bw.newLine();
bw.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}

Read File to String
Write String data to File starting from end.
For lines, use String array to store data from file and then traverse from end to start of array.
Here is complete program.
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.ArrayList;
import java.util.List;
public class Loading {
public static void main(String[] args) {
try {
BufferedReader br = new BufferedReader(new FileReader(
"DB.xml"));
String line, txt = "";
List<String> lines = new ArrayList<String>();
while ((line = br.readLine()) != null) {
lines.add(line);
}
System.out.println(txt);
br.close();
BufferedWriter bw = new BufferedWriter(new FileWriter("file2"));
for(int i=lines.size()-1; i>=0; i--){
bw.write(lines.get(i));
bw.newLine();
}
bw.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}

You're going to want a list of lines, since you don't know the number of entries beforehand, so you want something that can grow with your code.
List<String> lines = new ArrayList<String>();
And add all your lines to it
while ((line = br.readLine()) != null) {
lines.add(line);
}
Then write them to your file in reverse order:
for(int i = lines.size() - 1; i >= 0; i--) {
bw.write(lines.get(i));
bw.newLine();
}

Your code is concatenating the string incorrectly. It needs to add the line text to the beginning of the string rather than at the end if you are trying to reverse the order.
txt = line + txt + "\n"; //original: txt += linia + "\n"
But it would be better to use a StringBuilder object to handle the concatenation for you. Something like...
StringBuilder txt = new StringBuilder();
String line;
while ((line = br.readLine()) != null) {
txt.insert(0, line + "\n");
}
System.out.println(txt.toString());
I do agree that the array approach in the other answers would also work and is probably a little easier to read and maintain. But the StringBuilder approach is closer to what you already have.

It should work:
package test;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.ArrayList;
/**
*
* #author
*/
public class Read {
public static void main(String[] args) {
try {
BufferedReader br = new BufferedReader(new FileReader(
"D:/file.txt"));
String line, txt = "";
ArrayList<String> lines = new ArrayList<String>();
while ((line = br.readLine()) != null) {
lines.add(line);
}
System.out.println(txt);
br.close();
BufferedWriter bw = new BufferedWriter(new FileWriter("D:/file2.txt"));
for(int i = lines.size()-1; i>=0; i--){
bw.write(lines.get(i));
bw.newLine();
}
bw.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}