I am a newbie to Java and would be very grateful if someone could look into this code snippet and give me a hand.
#SuppressWarnings("unused")
public static void main(String[] args) throws IOException {
File fin = new File("wordList");
FileInputStream fis = new FileInputStream(fin);
BufferedReader br = new BufferedReader(new nputStreamReader(fis));
List<String> wordList = new ArrayList<>();
List<Character> guessedCharacters = new ArrayList<>();
char guessedCharacter;
String line = "";
while ((line = br.readLine()) != null) {
wordList.add(line);
}
br.close();
System.out.println("Welcome to hanged man.");
System.out.println();
for (int i = 0; i < wordList.size(); i++) {
System.out.print("Guess a letter: ");
guessedCharacter = (char) System.in.read();
System.out.println('\n');
}
When I run the code snippet above I get the following output:
Welcome to hanged man.
Guess a letter: d
Guess a letter:
Guess a letter:
My intention is to have the prompt "Guess a letter" appear only once after I enter the first letter.
If I replace "wordList.size()" in the for-loop with any integer larger than three I get the same result.
I hope to hear from someone. Thank you in advance. Marcos
What you are looking for is either using the Scanner class (probably not, as your exercise looks trivial and you probably just want the easiest way to read keyboard inputs without any GUI) or, most probably, this :
String answer = System.console().readLine("Guess a letter : ");
Don't use System.read() to read keystrokes (or unless you want to complicate things "just for the fun" :)
With System.read.in() you read 'd' and '\n' values. Try to use Scanner class (see here)
Related
I have a java program that reads from a cvs file that looks like this:
1111,John,23
2222,Mary,32
...
I want to store each field in an array. Whenever I run the following program I get the following message:
Exception in thread "main" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Scanner.java:862)
at java.util.Scanner.next(Scanner.java:1485)
at java.util.Scanner.nextInt(Scanner.java:2117)
at java.util.Scanner.nextInt(Scanner.java:2076)
How can I deal with that exception? I guess it is because scanner reads beyond its limit, however, doesn't the while block ensure that it will read within its limits?
Any help is appreciated
import java.util.*;
import java.io.*;
public class program
{
public static void main(String[] args) throws FileNotFoundException, IOException
{
BufferedReader br = new BufferedReader(new FileReader("info.csv"));
int[] ids = new int[20];
String[] names = new String[20];
int[] age = new int[20];
String line;
int i = 0;
while( (line = br.readLine()) != null)
{
Scanner s = new Scanner(line).useDelimiter(",");
ids[i] = s.nextInt();
names[i] = s.next();
sales[i] = s.nextInt();
s.close();
i++;
}
for(int j = 0; j < 20; j++)
{
System.out.println("Id: "+ids[i]+" Name: "+names[i]+" Age: "+ age[i]);
}
}
}
Reading CSV files is actually quite complicated. Handling quotes and newlines is quite difficult. There are also encoding issues to consider (which you haven't; you should basically never use this constructor FileReader, as it uses 'platform default encoding'). Don't reinvent this wheel; use something like super-csv.
The while block ensures you read each line once and don't read beyond the end of the file. Per line you forcibly go: an int, a string, and an int, period. That's where the crash occurs. Mostly likely there's a trailing newline at the end of the file or some such. A trivial example would be to check if line.trim() is empty, and if so, to just move on (continue;) and not attempt to read the line.
But, really, don't handroll this, get a CSV parser.
NB: If you must reinvent this wheel, there are far nicer and easier ways to get all lines from a file. For example, Files.newBufferedReader(Paths.get("/path/to/whatsit")) or even Files.lines(Paths.get("/path/to/whatsit")), conveniently those methods also default to UTF-8, i.e. a consistent choice instead of 'flip a coin and pray'.
Try to use split(,)
String[] split = line.split(",");
if (split.length >= 0) {
String input = split[0];
if (input.matches("[0-9]+"))
ids[i] = Integer.parseInt(input);
}
if (split.length >= 1) {
names[i] = split[1];
}
if (split.length >= 2) {
String input = split[2];
if (input.matches("[0-9]+"))
ids[i] = Integer.parseInt(input);
}
I´m in a bit of a struggle here, I´m trying to add each word from a textfile to an ArrayList and every time the reader comes across the same word again it will skip it. (Makes sense?)
I don't even know where to start. I kind of know that I need one loop that adds the textfile to the ArrayList and one the checks if the word is not in the list. Any ideas?
PS: Just started with Java
This is what I've done so far, don't even know if I'm on the right path..
public String findWord(){
int text = 0;
int i = 0;
while sc.hasNextLine()){
wordArray[i] = sc.nextLine();
}
if wordArray[i].contains() {
}
i++;
}
A List (an ArrayList or otherwise) is not the best data structure to use; a Set is better. In pseudo code:
define a Set
for each word
if adding to the set returns false, skip it
else do whatever do want to do with the (first time encountered) word
The add() method of Set returns true if the set changed as a result of the call, which only happens if the word isn't already in the set, because sets disallow duplicates.
I once made a similar program, it read through a textfile and counted how many times a word came up.
Id start with importing a scanner, as well as a file system(this needs to be at the top of the java class)
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.File;
import java.io.PrintStream;
import java.util.Scanner;
then you can make file, as well as a scanner reading from this file, make sure to adjsut the path to the file accordingly. The new Printstream is not necessary but when dealing with a big amount of data i dont like to overflow the console.
public static void main(String[] args) throws FileNotFoundException {
File file=new File("E:/Youtube analytics/input/input.txt");
Scanner scanner = new Scanner(file); //will read from the file above
PrintStream out = new PrintStream(new FileOutputStream("E:/Youtube analytics/output/output.txt"));
System.setOut(out);
}
after this you can use scanner.next() to get the next word so you would write something like this:
String[] array=new String[MaxAmountOfWords];//this will make an array
int numberOfWords=0;
String currentWord="";
while(scanner.hasNext()){
currentWord=scanner.next();
if(isNotInArray(currentWord))
{
array[numberOfWords]=currentWord
}
numberOfWords++;
}
If you dont understand any of this or need further guidence to progress, let me know. It is hard to help you if we dont exactly know where you are at...
You can try this:
public List<String> getAllWords(String filePath){
String line;
List<String> allWords = new ArrayList<String>();
BufferedReader reader = new BufferedReader(new FileReader(new File(filePath)));
//read each line of the file
while((line = reader.readLine()) != null) {
//get each word in the line
for(String word: line.split("(\\w)+"))
//validate if the current word is not empty
if(!word.isEmpty())
if(!allWords.contains(word))
allWords.add(word);
}
}
return allWords;
}
Best solution is to use a Set. But if you still want to use a List, here goes:
Suppose the file has the following data:
Hi how are you
I am Hardi
Who are you
Code will be:
List<String> list = new ArrayList<>();
// Get the file.
FileInputStream fis = new FileInputStream("C:/Users/hdinesh/Desktop/samples.txt");
//Construct BufferedReader from InputStreamReader
BufferedReader br = new BufferedReader(new InputStreamReader(fis));
String line = null;
// Loop through each line in the file
while ((line = br.readLine()) != null) {
// Regex for finding just the words
String[] strArray = line.split("[ ]");
for (int i = 0; i< strArray.length; i++) {
if (!list.contains(strArray[i])) {
list.add(strArray[i]);
}
}
}
br.close();
System.out.println(list.toString());
If your text file has sentences with special characters, you will have to write a regex for that.
I'm currently in an Introductory Java class at University and I'm having a bit of trouble. Last semester we started with Python and I became very acquainted with it and I would say I am proficient now in writing Python; yet Java is another story. Things are alot different. Anyway, Here is my current assignment: I need to write a class to search through a text document (passed as an argument) for a name that is inputted by the user and output whether or not the name is in the list. The first line of the text document is the amount of names in the list.
The text document:
14
Christian
Vincent
Joseph
Usman
Andrew
James
Ali
Narain
Chengjun
Marvin
Frank
Jason
Reza
David
And my code:
import java.util.*;
import java.io.*;
public class DbLookup{
public static void main(String[]args) throws IOException{
File inputDataFile = new File(args[0]);
Scanner stdin = new Scanner(System.in);
Scanner inFile = new Scanner(inputDataFile);
int length = inFile.nextInt();
String names[] = new String[length];
for(int i=0;i<length;i++){
names[i] = inFile.nextLine();
}
System.out.println("Please enter a name that you would like to search for: ");
while(stdin.hasNext()){
System.out.println("Please enter a name that you would like to search for: ");
String input = stdin.next();
for(int i = 0;i<length;i++){
if(input.equalsIgnoreCase(names[i])){
System.out.println("We found "+names[i]+" in our database!");
break;
}else{
continue;
}
}
}
}
}
I am just not getting the output I am expecting and I cannot figure out why.
Try this
You should trim() your values as they have extra spaces
if(input.trim().equalsIgnoreCase(names[i].trim()))
I have run your example it runs perfectly after using trim(), you have missed to trim()
Create a seperate scanner class to read line by line.You can use BufferedReader also.
final Scanner scanner = new Scanner(file);
while (scanner.hasNextLine()) {
final String str= scanner.nextLine();
if(str.contains(name)) {
// Found the input word
System.out.println("I found " +name+ " in file " +file.getName());
break;
}
}
If you use Java 8:
String[] names;
try (Stream<String> stream = Files.lines(Paths.get(fileName))) {
names = stream.skip(1).toArray(size -> new String[size]);
} catch (IOException e) {
e.printStackTrace();
}
In Java i take Input using standard Scanner and BufferedReader Classes like:
Scanner sc=new Scanner(System.in);
int a=sc.nextInt();
or
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
int a=Integer.parseInt(br.readLine());
but taking input like this takes a lot of running time. I would like to know the faster way to take input. Thanks in advance
Edit: I have seen top java coders like uwi who take input in a very different way. They kinda create their own reader class. I dont get it that how their program becomes fast in runtime.
In the article below, the author discusses three different ways for reading input from the user in the console. Each way is fairly easy to use and also has its own advantages and drawbacks.
The below mechanisms are discussed and examples are provided.
There is also a pros and cons section as well.
Link:
http://www.codejava.net/java-se/file-io/3-ways-for-reading-input-from-the-user-in-the-console
Link:
Most Efficient Way of Taking User Input in Java
Options:
Scanner Class->
Scanner reader = new Scanner(System.in); // Reading from System.in
System.out.println("Enter a number: ");
int n = reader.nextInt();
DataInputStream->
DataInputStream dis = new DataInputStream(System.in);
int i = dis.readInt();
BufferedReader ->
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
System.out.print("Enter your name: ");
String name = reader.readLine();
System.out.println("Your name is: " + name);
Console->
Console console = System.console();
String s = console.readLine();
int i = Integer.parseInt(console.readLine());
Quote from dejavu:
"BufferedReader is a lot faster than Scanner because it buffers the character so you don't have to access the file each time you want to read a char from it.
Scanner are of particular use such as reading primitive data type directly and is also used for regular expressions.
I have used Scanner and BufferedReader both and BufferedReader gives significant fast performance. You can test it yourself too."
from:which to choose buffered reader or scanner from performance point of view
If you want a fast way to input via stdin (and, if I understand you correctly, you want a fast way to repeatedly feed inputs to your programs), your best bet is to pipe or redirect canned responses e.g.
$ java MyReadingClass < mycannedinput.txt
so you can build your class to take interactive input via stdin, and then use a simple shell redirection to feed in canned input such that you don't have to retype it each time.
The Fastest way to take userinput in java in particularly Competitive coding is to make own FastReader class by using bufferedReader and StringTokenizer.
This method uses the time advantage of BufferedReader and StringTokenizer and the advantage of user defined methods for less typing and therefore a faster input altogether. This gets accepted with a time of 1.23 s and this method is very much recommended as it is easy to remember and is fast enough to meet the needs of most of the question in competitive coding.
Implementation :
static class FastReader
{
BufferedReader br;
StringTokenizer st;
public FastReader()
{
br = new BufferedReader(new
InputStreamReader(System.in));
}
String next()
{
while (st == null || !st.hasMoreElements())
{
try
{
st = new StringTokenizer(br.readLine());
}
catch (IOException e)
{
e.printStackTrace();
}
}
return st.nextToken();
}
int nextInt()
{
return Integer.parseInt(next());
}
long nextLong()
{
return Long.parseLong(next());
}
double nextDouble()
{
return Double.parseDouble(next());
}
String nextLine()
{
String str = "";
try
{
str = br.readLine();
}
catch (IOException e)
{
e.printStackTrace();
}
return str;
}
}
In Main File :
public static void main(String[] args)
{
FastReader s=new FastReader();
int n = s.nextInt();
int k = s.nextInt();
int count = 0;
while (n-- > 0)
{
int x = s.nextInt();
if (x%k == 0)
count++;
}
System.out.println(count);
}
Source Link : https://www.geeksforgeeks.org/fast-io-in-java-in-competitive-programming/
This is repeated question and an optimized way to read and write data in java can be found at the below link.
https://stackoverflow.com/a/49957378/5076337
These classes are very useful in reading inputs and writing outputs in programming contests.
In this program I am just getting input from a file and trying to get the boys name and the girls name out of it, and also put them in separate files. I have done everything just as the book has stated. And I've also searched everywhere online for help with this but cant seem to find anyone with the same problem. Ive seen problems where its not -1 but a positive number because they went to far out of the string calling a substring over the strings length. But cant seem to figure out this giving me -1 since i's value is 1.
import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Scanner;
import java.util.ArrayList;
public class Homework_11_1 {
public static void main(String[] args)throws FileNotFoundException
{
File inputFile = new File("babynames.txt");
Scanner in = new Scanner(inputFile);
PrintWriter outBoys = new PrintWriter("boys.txt");
PrintWriter outGirls = new PrintWriter("girls.txt");
while (in.hasNextLine()){
String line = in.nextLine();
int i = 0;
int b = 0;
int g = 0;
while(!Character.isWhitespace(line.charAt(i))){ i++; }
while(Character.isLetter(line.charAt(b))){ b++; }
while(Character.isLetter(line.charAt(g))){ g++; }
String rank = line.substring(i);
String boysNames = line.substring(i, b);
String girlsNames = line.substring(b, g);
outBoys.println(boysNames);
outGirls.println(girlsNames);
}
in.close();
outBoys.close();
outGirls.close();
System.out.println("Done");
}
}
Here is the txt file
1 Jacob Sophia
2 Mason Emma
3 Ethan Isabella
4 Noah Olivia
5 William Ava
6 Liam Emily
7 Jayden Abigail
8 Michael Mia
9 Alexander Madison
10 Aiden Elizabeth
I would have written it an other way, using split.
public static void main(String[] args)throws FileNotFoundException
{
File inputFile = new File("babynames.txt");
Scanner in = new Scanner(inputFile);
PrintWriter outBoys = new PrintWriter("boys.txt");
PrintWriter outGirls = new PrintWriter("girls.txt");
while (in.hasNextLine()){
String line = in.nextLine();
String[] names = line.split(" "); // wile give you [nbr][boyName][GirlName]
String boysNames = names[1];
String girlsNames = names[2];
outBoys.println(boysNames);
outGirls.println(girlsNames);
}
in.close();
outBoys.close();
outGirls.close();
System.out.println("Done");
}
Rather than fuss with loops and substring(), I'd just use String.split(" "). Of course, the assignment may not permit you to do this.
But anyway, without giving you the answer to the assignment, I can tell you that your logic is wrong. Walk through it and find out why. If you try running this code on just the first line of the input file, you'll get these values: i=1, b=0, and g=0. Calling line.substring(1,0) is obviously not going to work.