Develop Reference

Displaying the contents of a textfile by typing the filename in a java program?

Write a program that reads in a file and displays its contents. Get the input filename from the command line. For example, if your program is in the file Display.class, you would enter on the command line:
java Display t1.txt
to display the content file t1.txt.
How can this be done?

you can use FileReader or BufferedReader to read the contents of file. below code may be helpful to you
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
public class Display {
public static void main(String[] args) {
if(args.length > 0) {
String fileName = args[0];
try {
File file = new File(fileName);
if(file.exists() && file.isFile() ) {
BufferedReader br = new BufferedReader(new FileReader(file));
String line = null;
System.out.println("FileContents are...");
while((line = br.readLine()) != null) {
System.out.println(line);
}
}else{
System.out.println("File Not Found");
}
} catch (FileNotFoundException e) {
System.out.println("File Not Found");
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

Java Writing to a file: does not write to all desired files

I am out of ideas, I've been trying for the whole day to separate one file which has a format of :
AN Aixas
AN Aixirivall
AN Aixovall
AN Andorra la Vella
BR Salto do Mandira
BR Salto do Norte
BR Salto Dollman
BR Salto Grande
BR Salto Pilao
...
and so one, into different files by the name of the Country "AA.txt" and to include all the cities in these separate files. But my program only writes to a certain bunch of files and I cannot figure out why.
I've tried all the writing files classes - same result.
Here is the result, all worked but on a certain bunch of files only.
Here is the code :
package com.fileorganizer;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
public class File2 implements Cloneable {
static InputStream fis = null;
static BufferedReader br = null;
static String state = "";
static String tmp = "";
static File file = null;
static FileWriter fw = null;
static BufferedWriter bw = null;
public static void main(String[] args) {
int a = 0;
try {
fis = new FileInputStream(
new File(
"/Users/Mihail/Documents/WorkSpace/Parse-Starter-Project-1.8.2/ParseStarterProject/res/raw/cities.txt"));
br = new BufferedReader(new InputStreamReader(fis));
String line = null;
while ((line = br.readLine()) != null) {
state = line.substring(0, 2);
if (state.substring(0, 1).matches("^[A-Z]+$")
&& state.substring(1, 2).matches("^[A-Z]+$")
&& !tmp.equals(state)) {
file = new File(
"/Users/Mihail/Documents/WorkSpace/Parse-Starter-Project-1.8.2/ParseStarterProject/res/raw/countriesFolder/"
+ state + ".txt");
fw = new FileWriter(file.getAbsoluteFile());
bw = new BufferedWriter(fw);
tmp = state;
}
bw.write(line.substring(3) + "\n");
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (br != null)
br.close();
} catch (Exception ex) {
}
}
}
}
I am really sorry for such a dumb question. Please help

You don't close bw anywhere, so the contents in the BufferedWriter's buffer are lost.

Reading text file into String array, then converting to ArrayList

How can I read a file into a array of String[] and then convert it into ArrayList?
I can't use an ArrayList right away because my type of list is not applicable for the arguments (String).
So my prof told me to put it into an array of String, then convert it.
I am stumped and cannot figure it out for the life of me as I am still very new to java.

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
/**
* Created by tsenyurt on 06/04/15.
*/
public class ReadFile
{
public static void main(String[] args) {
List<String> strings = new ArrayList<>();
BufferedReader br = null;
try {
String sCurrentLine;
br = new BufferedReader(new FileReader("/Users/tsenyurt/Development/Projects/java/test/pom.xml"));
while ((sCurrentLine = br.readLine()) != null) {
System.out.println(sCurrentLine);
strings.add(sCurrentLine);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (br != null)br.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
}
there is a code that reads a file and create a ArrayList from it
http://www.mkyong.com/java/how-to-read-file-from-java-bufferedreader-example/

Well there are many ways to do that,
you can use this code if you want have a List of each word exist in your file
public static void main(String[] args) {
BufferedReader br = null;
StringBuffer sb = new StringBuffer();
List<String> list = new ArrayList<>();
try {
String sCurrentLine;
br = new BufferedReader(new FileReader(
"Your file path"));
while ((sCurrentLine = br.readLine()) != null) {
sb.append(sCurrentLine);
}
String[] words = sb.toString().split("\\s");
list = Arrays.asList(words);
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (br != null)
br.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
for (String string : list) {
System.out.println(string);
}
}

Code deletes the content of the file rather than replacing a text

In my below code I wanted to replace the text "DEMO" with "Demographics" but instead of replacing the text it deletes the entire content of the text file.
Contents inside the file:
DEMO
data
morning
PS: I'm a beginner in java
package com.replace.main;
import java.io.*;
public class FileEdit {
public static void main(String[] args) {
BufferedReader br = null;
BufferedWriter bw = null;
String readLine, replacedData;
try {
bw = new BufferedWriter(
new FileWriter(
"Demg.ctl"));
br = new BufferedReader(
new FileReader(
"Demg.ctl"));
System.out.println(br.readLine()); //I Get Null Printed Here
while ((readLine = br.readLine())!= null) {
System.out.println("Inside While Loop");
System.out.println(readLine);
if (readLine.equals("DEMO")) {
System.out.println("Inside if loop");
replacedData = readLine.replaceAll("DEMO","Demographics");
}
}
System.out.println("After While");
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

You open a Writer to your file, but you don't write anything. This means that your file is replaced with an empty file.
Besides this you also need to close your writer, not just the reader.
And last but not least, your if condition is wrong.
if (readLine.equals("DEMO")) {
should read
if (readLine.contains("DEMO")) {
Otherwise it would only return true if your line contained "DEMO" but nothing else.

I'm updating the answer to my own question.
package com.replace.main;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class FileEdit
{
public static void main(String args[])
{
try
{
BufferedReader reader = new BufferedReader(new FileReader("Demg.ctl"));
String readLine = "";
String oldtext = "";
while((readLine = reader.readLine()) != null)
{
oldtext += readLine + "\r\n";
}
reader.close();
// To replace the text
String newtext = oldtext.replaceAll("DEMO", "Demographics");
FileWriter writer = new FileWriter("Demg.ctl");
writer.write(newtext);
writer.close();
}
catch (IOException e)
{
e.printStackTrace();
}
}
}

Unable to rename file

I was trying an exercise of deleting lines from a file not starting with a particular string.
The idea was to copy the desired lines to a temp file, delete the original file and rename the temp file to original file.
My question is I am unable to rename a file!
tempFile.renameTo(new File(file))
or
tempFile.renameTo(inputFile)
do not work.
Can anyone tell me what is going wrong? Here is the code:
/**
* The intention is to have a method which would delete (or create
* a new file) by deleting lines starting with a particular string. *
*/
package com.dr.sort;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
public class RemoveLinesFromFile {
public void removeLinesStartsWith(String file, String startsWith, Boolean keepOrigFile) {
String line = null;
BufferedReader rd = null;
PrintWriter wt = null;
File tempFile = null;
try {
// Open input file
File inputFile = new File(file);
if (!inputFile.isFile()) {
System.out.println("ERROR: " + file + " is not a valid file.");
return;
}
// Create temporary file
tempFile = new File(file + "_OUTPUT");
//Read input file and Write to tempFile
rd = new BufferedReader(new FileReader(inputFile));
wt = new PrintWriter(new FileWriter(tempFile));
while ((line = rd.readLine()) != null) {
if (line.substring(0, startsWith.length()).equals(startsWith)) {
wt.println(line);
wt.flush();
}
}
rd.close();
if (!keepOrigFile) {
inputFile.delete();
if (tempFile.renameTo(new File(file))) {
System.out.println("OK");
} else {
System.out.println("NOT OK");
}
}
}
catch (FileNotFoundException ex) {
ex.printStackTrace();
} catch (IOException ex) {
ex.printStackTrace();
}
finally {
if (tempFile != null && tempFile.isFile()) {
wt.close();
}
}
}
}

I guess you need to close your PrintWriter before renaming.

if (line.substring(0, startsWith.length()).equals(startsWith))
should instead be the opposite, because we don't want the lines that are specified to be included.
so:
if (!line.substring(0, startsWith.length()).equals(startsWith))