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how to update the file without creating new file

My code does not update the exist file. So i create new file but i want to do with the same file and update it. Anyone know how to do it ? my code is here and a picture of what im doing
try (BufferedWriter writer = new BufferedWriter(new FileWriter("project-output.csv"))) {
try (BufferedReader reader = new BufferedReader(new FileReader("project.csv"))) {
String line;
while ((line = reader.readLine()) != null) {
String[] cols = line.split(",");
System.out.println("Please choose a criteria (2-7): ");
final int subjectToGiveMark = in.nextInt(); // for creativity is 2
System.out.println("Please enter a mark: ");
final int mark = in.nextInt(); // which mark should be given
cols[subjectToGiveMark] = Integer.toString(mark);
// Here is where you write the output:
writer.write(String.join(",", cols));
writer.newLine();
}
writer.flush();
}
}
enter image description here

Do it as follows:
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 Main {
public static void main(String[] args) {
String line;
List<String> dataLines = new ArrayList<String>();
final int COLS = 6;
String[][] data = null;
try (BufferedReader br = new BufferedReader(new FileReader("project.csv"))) {
while ((line = br.readLine()) != null) {
dataLines.add(line);
}
// Initialise data[][] with the data from project.csv
data = new String[dataLines.size()][COLS];
for (int i = 0; i < dataLines.size(); i++) {
data[i] = dataLines.get(i).split(",");// Split on comma
}
// Display Sarah's marks in Achievement (15)
System.out.println(data[2][1] + "'s marks in Achievement (15) is " + data[2][3]);
// Display Harry's marks in Knowledge (25)
System.out.println(data[3][1] + "'s marks in Knowledge (25) is " + data[3][4]);
} catch (Exception e) {
e.printStackTrace();
}
// Update the file
try (BufferedWriter writer = new BufferedWriter(new FileWriter("project.csv"))) {
// Increasing Sarah's marks in Achievement by 1
int m = Integer.parseInt(data[2][3]) + 1;
data[2][3] = String.valueOf(m);
// Decreasing Harry's marks in Knowledge by 1
m = Integer.parseInt(data[3][4]) - 1;
data[3][4] = String.valueOf(m);
//Write the updated data to file
for (String[] row : data) {
writer.write(String.join(",", row) + System.lineSeparator());
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
Output:
Sarah's marks in Achievement (15) is 13
Harry's marks in Knowledge (25) is 24
Original content of project.csv:
Student Id,Student Name,Creativity (10),Achievement (15),Knowledge (25),Documentation (25)
F1233,Bill,8,12,20,18
F2345,Sarah,9,13,22,23
F3456,Harry,9,14,24,24
New content of project.csv:
Student Id,Student Name,Creativity (10),Achievement (15),Knowledge (25),Documentation (25)
F1233,Bill,8,12,20,18
F2345,Sarah,9,14,22,23
F3456,Harry,9,14,23,24
Example of updating the data interactively:
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class Main {
public static void main(String[] args) throws FileNotFoundException, IOException {
String line;
List<String> dataLines = new ArrayList<String>();
final int COLS = 6;
String[][] data = null;
try (BufferedReader br = new BufferedReader(new FileReader("project.csv"))) {
while ((line = br.readLine()) != null) {
dataLines.add(line);
}
// Initialise data[][] with the data from project.csv
data = new String[dataLines.size()][COLS];
for (int i = 0; i < dataLines.size(); i++) {
data[i] = dataLines.get(i).split(",");// Split on comma
}
}
// Update the file
try (BufferedWriter writer = new BufferedWriter(new FileWriter("project.csv"))) {
Scanner in = new Scanner(System.in);
// Updating existing record
System.out.println("Updating " + data[2][1] + "'s marks in a subject...");
System.out.print(
"Enter the subject number[2 for Creativity, 3 for Achievement, 4 for Knowledge, 5 for Documentation]: ");
int col = Integer.parseInt(in.nextLine());
if (col >= 2 && col <= 5) {
System.out.print("Enter marks in the subject: ");
data[2][col] = in.nextLine();
// Write the updated data to file
for (String[] row : data) {
writer.write(String.join(",", row) + System.lineSeparator());
}
}
// Adding a new record
System.out.println("Adding a new record...");
String[] record = new String[COLS];
System.out.print("Enter student ID: ");
record[0] = in.nextLine();
System.out.print("Enter student name: ");
record[1] = in.nextLine();
System.out.print(
"Enter marks in Creativity (10), Achievement (15), Knowledge (25), and Documentation (25): ");
System.arraycopy(in.nextLine().split("\\s+"), 0, record, 2, COLS - 2);
writer.write(String.join(",", record) + System.lineSeparator());
}
}
}
A sample run:
Updating Sarah's marks in a subject...
Enter the subject number[2 for Creativity, 3 for Achievement, 4 for Knowledge, 5 for Documentation]: 2
Enter marks in the subject: 7
Adding a new record...
Enter student ID: F4567
Enter student name: Richard
Enter marks in Creativity (10), Achievement (15), Knowledge (25), and Documentation (25): 8 12 20 21
New content of project.csv:
Student Id,Student Name,Creativity (10),Achievement (15),Knowledge (25),Documentation (25)
F1233,Bill,8,12,20,18
F2345,Sarah,7,14,22,23
F3456,Harry,9,14,23,24
F4567,Richard,8,12,20,21

can you try
// Read existing file
CSVReader reader = new CSVReader(new FileReader(inputFile), ',');
List<String[]> csvBody = reader.readAll();
// get CSV row column and replace with by using row and column
csvBody.get(row)[col] = replace;
reader.close();
// Write to CSV file which is open
CSVWriter writer = new CSVWriter(new FileWriter(inputFile), ',');
writer.writeAll(csvBody);
writer.flush();
writer.close();

How to add only unique values from CSV into ComboBox?

I want to read a csv File and put words " Jakarta " and " Bandung " in a combobox. Here's the input
id,from,
1,Jakarta
2,Jakarta
5,Jakarta
6,Jakarta
10,Bandung
11,Bandung
12,Bandung
I managed to get the words and put it in the combobox, but as you can see, the text file itself contains a lot word " Jakarta " and " Bandung " while i want to show both only once in the combobox.
Here's my temporary code, which works for now but inefficient and probably can't be used if the word has more variety
public String location;
private void formWindowOpened(java.awt.event.WindowEvent evt) {
String csvFile = "C:\\Users\\USER\\Desktop\\Project Data.csv";
BufferedReader br = null;
LineNumberReader reader = null;
String line = "";
String cvsSplitBy = "-|\\,";
br = new BufferedReader(new FileReader(csvFile));
reader = new LineNumberReader(new FileReader(csvFile));
while ((line = br.readLine()) != null) {
// use comma as separator
String[] bookingdata = line.split(cvsSplitBy);
location = bookingdata[1];
ComboBoxModel model = cmb1.getModel();
int size = model.getSize();
cmb1.addItem(location);
for(int i = 1; i < size; i++){
if(model.getElementAt(i).equals("from")){
cmb1.removeItemAt(i);
}
else if(model.getElementAt(i).equals("Bandung")){
cmb1.removeItemAt(i);
}
for(int j = 2; j < i; j++){
if(model.getElementAt(j).equals("Jakarta")){
cmb1.removeItemAt(j);
}
}
}
}
}
Someone else recommended this approach
boolean isEquals = false;
for(i = 0; i < a && !isEquals; i++){
isEquals = location.equals("Jakarta");
if(isEquals){
cmb1.addItem("Jakarta");
}
}
This code doesn't work. As the code doesn't stop once it adds a " Jakarta " but it stops after it completed a loop. thus it still creates duplicate within the combobox.
I would like to know if there's any other code i can try. Thank you

Try putting all the words in a Set first and then add it in the combobox. Set itself will take care of exact one occurrence of each word.
Something like this:
while ((line = br.readLine()) != null) {
// use comma as separator
String[] bookingdata = line.split(cvsSplitBy);
location = bookingdata[1];
ComboBoxModel model = cmb1.getModel();
int size = model.getSize();
// add all location in set and set will only allow distinct values
locationSet.add(location);
}
// after looping through all location put it in combobox
for(String location:locationSet)cmb1.addItem(location);
}
}
As discussed in comments, Sets are meant to keep unique values. Please find the screenshot of JShell below:
PS: This is just to give an idea and may need some amendment as per requirement.
--EDITED--
As discussed, it seems you are still missing something, I tried and write below piece of code and worked fine
package com.digital.core;
import java.util.HashSet;
import java.util.Set;
import javax.swing.JComboBox;
import javax.swing.JFrame;
public class Test {
public static void main(String[] args) {
JFrame jframe = new JFrame();
jframe.setSize(300, 300);
String data = "id,from,\n" +
"1,Jakarta\n" +
"2,Jakarta\n" +
"5,Jakarta\n" +
"6,Jakarta\n" +
"10,Bandung\n" +
"11,Bandung\n" +
"12,Bandung";
String[] dataArr = data.split("\n");
Set<String> locationSet = new HashSet<>();
for(String line:dataArr) {
locationSet.add(line.split(",")[1]);
}
JComboBox<String> comboBox = new JComboBox<>();
for(String location:locationSet)
comboBox.addItem(location);
jframe.add(comboBox);
jframe.setVisible(true);
}
}

You could create an ObservablArrayList of strings and as you read the CSV file, check if the list already contains that string:
ObservableList<String> locationsList = FXCollections.observableArrayList();
// Add your strings to the array as they're loaded, but check to
// make sure the string does not already exist
if (!locationsList.contains(location)) {
locationsList.add(location);
}
Then, after reading the whole file and populating the list, just set the items in your combobox to that ObservableArrayList.

how to link a main class to a jframe form in java using netbeans

Good day!
I have created a code using Netbeans and it executes the processes just fine.
Now, i want my input to given and output to be displayed through a user interface. I have then created a 2 Jframes, 1 to collect the user's input and the other to display the results after execution by the code.
But, i am unable to link the interface to the main class(called NgramBetaE) as i am not aware of how i can do so.
I highly welcome suggestions.
The main class in its entirety is;
package ngrambetae;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.*;
/**
*
* #author 201102144
*/
public class NgramBetaE {
static LinkedList<String> allWords = new LinkedList<String>();
static LinkedList<String> distinctWords = new LinkedList<String>();
static String[] hashmapWord = null;
static int wordCount;
public static HashMap<String,HashMap<String, Integer>> hashmap = new HashMap<>();
public static HashMap<String,HashMap<String, Integer>> bigramMap = new HashMap<>();
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
//prompt user input
Scanner input = new Scanner(System.in);
//read words from collected corpus; a number of .txt files
File directory = new File("Corpus");
File[] listOfFiles = directory.listFiles();//To read from all listed iles in the "directory"
int lineNumber = 0;
String line;
String files;
String delimiters = "[()?!:;,.\\s]+";
//reading from a list of text files
for (File file : listOfFiles) {
if (file.isFile()) {
files = file.getName();
try {
if (files.endsWith(".txt") || files.endsWith(".TXT")) { //ensures a file being read is a text file
BufferedReader br = new BufferedReader(new FileReader(file));
while ((line = br.readLine()) != null) {
line = line.toLowerCase();
hashmapWord = line.split(delimiters);
//CALCULATING UNIGRAMS
for(int s = 0; s < hashmapWord.length; s++){
String read = hashmapWord[s];
allWords.add(read);
//count the total number of words in all the text files combined
//TEST
wordCount = 0;
for (int i = 0; i < allWords.size(); i++){
wordCount ++;
}
}
//CALCULATING BIGRAM FREQUENCIES
for(int s = 0; s < hashmapWord.length -1; s++){
String read = hashmapWord[s];
final String read1 = hashmapWord[s + 1];
HashMap<String, Integer> counter = bigramMap.get(read);
if (null == counter) {
counter = new HashMap<String, Integer>();
bigramMap.put(read, counter);
}
Integer count = counter.get(read1);
counter.put(read1, count == null ? 1 : count + 1);
}
//CALCULATING TRIGRAM FREQUENCIES
for(int s = 0; s < hashmapWord.length - 2; s++){
String read = hashmapWord[s];
String read1 = hashmapWord[s + 1];
final String read2 = hashmapWord[s + 2];
String readTrigrams = read + " " + read1;
HashMap<String, Integer> counter = hashmap.get(readTrigrams);
if (null == counter) {
counter = new HashMap<String, Integer>();
hashmap.put(readTrigrams, counter);
}
Integer count = counter.get(read2);
counter.put(read2, count == null ? 1 : count + 1);
}
}
br.close();
}
} catch (NullPointerException | IOException e) {
e.printStackTrace();
System.out.println("Unable to read files: " + e);
}
}
}
//COMPUTING THE TOTAL NUMBER OF WORDS FROM ALL THE TEXT FILES COMBINED
System.out.println("THE TOTAL NUMBER OF WORDS IN COLLECTED CORPUS IS : \t" + wordCount + "\n");
for(int i = 0, size = allWords.size(); i < size; i++){
String distinctWord = allWords.get(i);
//adding a word into the 'distinctWords' list if it doesn't already occur
if(!distinctWords.contains(distinctWord)){
distinctWords.add(distinctWord);
}
}
//PRINTING THE DISTINCT WORDS
System.out.println("THE DISTINCT WORDS IN TOTAL ARE :\t " + distinctWords.size() + "\n");
System.out.println("PRINTING CONTENTS OF THE BIGRAMS HASHMAP... ");
System.out.println(bigramMap);
System.out.println("================================================================================================================================================================================================================================================================================================================\n");
System.out.println("PRINTING CONTENTS OF THE TRIGRAMS HASHMAP... ");
System.out.println(hashmap);
System.out.println("================================================================================================================================================================================================================================================================================================================\n");
//QUITTING APPLICATION
String userInput = null;
while(true) {
System.out.println("\n**********************************************************************************************************************************************************************************************************************************");
System.out.println("\n\n\t\tPLEASE ENTER A WORD OR PHRASE YOU WOULD LIKE A PREDICTION OF THE NEXT WORD FROM:");
System.out.println("\t\t\t\t(OR TYPE IN 'Q' OR 'q' TO QUIT)");
userInput = input.nextLine();
if (userInput.equalsIgnoreCase("Q")) break;
//FORMAT USER INPUT
String[] users = userInput.toLowerCase().split("[?!,.\\s]+");
if (users.length < 2) {
userInput = users[0];
//System.out.println("\nENTRY '" + userInput + "' IS TOO SHORT TO PREDICT NEXT WORD. PLEASE ENTER 2 OR MORE WORDS");
//CALCULATING BIGRAM PROBABILITY
int sum = 0;
try {
for(String s : bigramMap.get(userInput).keySet()) {
sum += bigramMap.get(userInput).get(s);
}
String stringHolder = null;
double numHolder = 0.0;
for(String s : bigramMap.get(userInput).keySet()) {
//System.out.println("TWO");
double x = Math.round(bigramMap.get(userInput).put(s, bigramMap.get(userInput).get(s))/ (double)sum *100 );
if(s != null){
if(numHolder < x ){
stringHolder = s;
numHolder = x;
}
}
}
System.out.println("\nNEXT WORD PREDICTED IS '" + stringHolder + "'");
System.out.println("ITS PROBABILITY OF OCCURRENCE IS " + numHolder + "%");
} catch (Exception NullPointerException) {
System.out.println("\nSORRY. MATCH NOT FOUND.");
}
} else {
userInput = users[users.length - 2] + " " + users[users.length - 1];
// System.out.println("FROM USER WE GET....");
// System.out.println(bigrams.get(userInput).keySet());
/* CALCULATING TRIGRAM PROBABILITY*/
int sum = 0;
try {
for(String s : hashmap.get(userInput).keySet()) {
sum += hashmap.get(userInput).get(s);
}
String stringHolder = null;
double numHolder = 0.0;
for(String s : hashmap.get(userInput).keySet()) {
//System.out.println("TWO");
double x = Math.round(hashmap.get(userInput).put(s, hashmap.get(userInput).get(s))/ (double)sum *100 );
if(s != null){
if(numHolder < x ){
stringHolder = s;
numHolder = x;
}
}
}
System.out.println("\nNEXT WORD PREDICTED IS '" + stringHolder + "'");
System.out.println("ITS PROBABILITY OF OCCURRENCE IS " + numHolder + "%");
} catch (Exception NullPointerException) {
System.out.println("\nSORRY. MATCH NOT FOUND.");
}
}
}
input.close();
}
}
My first Jframe which i would like to appear upon running the project has got a single textbox and a single button;
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
String usersInput = jTextField1.getText();
Interface1 s = new Interface1();
s.setVisible(true);
dispose();
}
i would like for the user to enter data in the textbox and when they click on the button 'predict next word' then the output from the code execution is displayed on the second jframe which has got 3 labels and relative text areas.
NOTE; i couldn't paste the screenshots but if you run the NgramBetaE class you will get an idea of how the interfaces will be as i tried to explain them.
Thank you

Don't even try to link your GUI code to your NgramBetaE code as you've more work to do since the NgramBetaE is little more than one huge static main method that gets user input from the console with a Scanner and outputs to the console via printlns. Melding these two is like trying to put a square peg into a round hole.
Instead re-write the whole thing with an eye towards object-oriented coding, including creation of an OOP-compliant model class with instance fields and methods, and a single GUI that gets the input and displays it, that holds an instance of the model class and that calls instance methods on this instance.
Consider creating non-GUI classes and methods for --
Reading in data from your text files
Analyzing and hashing the data held in the text files including calculating word frequencies etc...
Returning needed data after analysis in whatever data form it may be needed.
A method for allowing input of a String/phrase for testing, with return its predicted probability
Then create GUI code for:
Getting selected text file from the user. A JFileChooser and supporting code works well here.
Button to start analysis
JTextField to allow entering of phrase
JTextArea or perhaps JTable to display results of analysis
Note that you should avoid having more than one JFrame in your GUI. For more on this, please have a look at The Use of Multiple JFrames, Good/Bad Practice?

Calculating the frequency of strings as they get stored in a nested hashmap

i want to write a code that stores strings in a hashmap as they are read from text files.
i have written the code below and it works, no errors, the frequency of every occurrence of the string combination does not change, it is always 1.
i am asking for assistance on how i can ensure that if a string combination appears more than once in the text file then its frequency should also increase.
this is my code:
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.*;
public class NgramBetaC {
static String[] hashmapWord = null;
public static Map<String,Map<String, Integer>> bigrams = new HashMap<>();
public static void main(String[] args) {
//prompt user input
Scanner input = new Scanner(System.in);
//read words from collected corpus; a number of .txt files
File directory = new File("Corpus4");
File[] listOfFiles = directory.listFiles();//To read from all listed iles in the "directory"
//String bWord[] = null;
int lineNumber = 0;
String line;
String files;
String delimiters = "[\\s+,?!:;.]";
int wordTracker = 0;
//reading from a list of text files
for (File file : listOfFiles) {
if (file.isFile()) {
files = file.getName();
try {
if (files.endsWith(".txt") || files.endsWith(".TXT")) { //ensures a file being read is a text file
BufferedReader br = new BufferedReader(new FileReader(file));
while ((line = br.readLine()) != null) {
line = line.toLowerCase();
hashmapWord = line.split(delimiters);
for(int s = 0; s < hashmapWord.length - 2; s++){
String read = hashmapWord[s];
String read1 = hashmapWord[s + 1];
final String read2 = hashmapWord[s + 2];
String readBigrams = read + " " + read1;
final Integer count = null;
//bigrams.put(readBigrams, new HashMap() {{ put (read2, (count == null)? 1 : count + 1);}});
bigrams.put(readBigrams, new HashMap<String, Integer>());
bigrams.get(readBigrams).put(read2, (count == null) ? 1 : count+1);
} br.close();
}
}
} catch (NullPointerException | IOException e) {
e.printStackTrace();
System.out.println("Unable to read files: " + e);
}
}
}
}
THE LINES CONTAINED IN THE TEXT FILES ARE::
1.i would like some ice cream.
2.i would like to be in dubai this december.
3.i love to eat pasta.
4.i love to prepare pasta myself.
5.who will be coming to see me today?
THE OUTPUT I GET WHEN PRINTING CONTENTS OF THE HASHMAP IS:
{coming to={see=1}, would like={to=1}, in dubai={this=1}, prepare pasta={myself=1}, to eat={pasta=1}, like to={be=1}, to prepare={pasta=1}, will be={coming=1}, love to={prepare=1}, some ice={cream=1}, be in={dubai=1}, be coming={to=1}, dubai this={december=1}, to be={in=1}, i love={to=1}, to see={me=1}, who will={be=1}, like some={ice=1}, i would={like=1}, see me={today=1}}
Please assist! some string combinations are not even appearing.
THE OUTPUT I EXPECT AS I READ FROM THE FILES IS:
{coming to={see=1}, would like={to=1}, in dubai={this=1}, prepare pasta={myself=1}, to eat={pasta=1}, like to={be=1}, to prepare={pasta=1}, will be={coming=1}, love to={prepare=1}, some ice={cream=1}, be in={dubai=1}, be coming={to=1}, dubai this={december=1}, to be={in=1}, i love={to=1}, to see={me=1}, who will={be=1}, like some={ice=1}, i would={like=2}, see me={today=1}, love to {eat=1}, would like {some=1}, i would {love=1}, would love {to=1}}

Tentatively update the current structure without overwriting the originl content
Replace
bigrams.put(readBigrams, new HashMap<String, Integer>());
bigrams.get(readBigrams).put(read2, (count == null) ? 1 : count+1);
With
HashMap<String, Integer> counter = bigrams.get(readBigrams);
if (null == counter) {
counter = new HashMap<String, Integer>();
bigrams.put(readBigrams, counter);
}
Integer count = counter.get(read2);
counter.put(read2, count == null ? 1 : count + 1);

Searching for strings in a text file

I was programing in Python but now I want to do the same code in Java. Can you help me please? This is the code that I was working on
import random
import re
a = "y"
while a == "y":
i = input('Search: ')
b = i.lower()
word2 = ""
for letter in b:
lista = []
with open('d:\lista.txt', 'r') as inF:
for item in inF:
if item.startswith(letter):
lista.append(item)
word = random.choice(lista)
word2 = word2 + word
print(word2)
a = input("Again? ")
Now I want to do the same on Java but Im not really sure how to do it. Its not that easy. Im just a beginner. So far I founded a code that makes the search in a text file but I'm stuck.
This is the java code. It finds the position of the word. I've been trying to modify it without the results Im looking for.
import java.io.*;
import java.util.Scanner;
class test {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.println("Search: ");
String searchText = input.nextLine();
String fileName = "lista.txt";
StringBuilder sb = new StringBuilder();
try {
BufferedReader reader = new BufferedReader(new FileReader(fileName));
while (reader.ready()) {
sb.append(reader.readLine());
}
}
catch(IOException ex) {
ex.printStackTrace();
}
String fileText = sb.toString();
System.out.println("Position in file : " + fileText.indexOf(searchText));
}
}
What I want is to find an item in a text file, a list, but just want to show the items that begin with the letters of the string I want to search. For example, I have the string "urgent" and the text file contains:
baby
redman
love
urban
gentleman
game
elephant
night
todd
So the display would be "urban"+"redman"+"gentleman"+ until it reaches the end of the string.

Let's assume that you've already tokenized the string so you've got a list of Strings, each containing a single word. It's what comes from the reader if you've got one word per line, which is how your Python code is written.
String[] haystack = {"baby", "redman", "love", "urban", "gentleman", "game",
"elephant", "night", "todd"};
Now, to search for a needle, you can simply compare the first characters of your haystack to all characters of the needle :
String needle = "urgent";
for (String s : haystack) {
for (int i = 0; i < needle.length(); ++i) {
if (s.charAt(0) == needle.charAt(i)) {
System.out.println(s);
break;
}
}
}
This solutions runs in O(|needle| * |haystack|).
To improve it a bit for the cost of a little bit of extra memory, we can precompute a hash table for the available starts :
String needle = "urgent";
Set<Character> lookup = new HashSet<Character>();
for (int i = 0; i < needle.length(); ++i) {
lookup.add(needle.charAt(i));
}
for (String s : haystack) {
if (lookup.contains(s.charAt(0))) {
System.out.println(s);
}
}
The second solution runs in O(|needle| + |haystack|).

This works if your list of words isn't too large. If your list of words is large you could adapt this so that you stream over the file multiple time collecting words to use.
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Random;
public class Test {
public static void main(String[] args) {
Map<Character, List<String>> map = new HashMap<Character, List<String>>();
File file = new File("./lista.txt");
BufferedReader reader = null;
try {
reader = new BufferedReader(new FileReader(file));
String line = null;
while ((line = reader.readLine()) != null) {
// assumes words are space separated with no
// quotes or commas
String[] tokens = line.split(" ");
for(String word : tokens) {
if(word.length() == 0) continue;
// might as well avoid case issues
word = word.toLowerCase();
Character firstLetter = Character.valueOf(word.charAt(0));
List<String> wordsThatStartWith = map.get(firstLetter);
if(wordsThatStartWith == null) {
wordsThatStartWith = new ArrayList<String>();
map.put(firstLetter, wordsThatStartWith);
}
wordsThatStartWith.add(word);
}
}
Random rand = new Random();
String test = "urgent";
List<String> words = new ArrayList<String>();
for (int i = 0; i < test.length(); i++) {
Character key = Character.valueOf(test.charAt(i));
List<String> wordsThatStartWith = map.get(key);
if(wordsThatStartWith != null){
String randomWord = wordsThatStartWith.get(rand.nextInt(wordsThatStartWith.size()));
words.add(randomWord);
} else {
// text file didn't contain any words that start
// with this letter, need to handle
}
}
for(String w : words) {
System.out.println(w);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if(reader != null) {
try {
reader.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
}
This assumes the content of lista.txt looks like
baby redman love urban gentleman game elephant night todd
And the output will look something like
urban
redman
gentleman
elephant
night
todd