I have a text file of names( last and first). I have successfully been able to use RandomAccessFile class to load all the names into an Array of strings. What is left for me to do, is to assign each of the first names to an Array of first names and each of the last names in the list to an array of Last Names. Here is what I did but Im not getting any desired result.
public static void main(String[] args) {
String fname = "src\\workshop7\\customers.txt";
String s;
String[] Name;
String[] lastName, firstName;
String last, first;
RandomAccessFile f;
try {
f = new RandomAccessFile(fname, "r");
while ((s = f.readLine()) != null) {
Name = s.split("\\s");
System.out.println(Arrays.toString(Name));
for (int i = 0; i < Name.length; i++) {
first = Name[0];
last = Name[1];
System.out.println("last Name: " + last + "First Name: "+ first);
}
}
f.close();
} catch (Exception ex) {
System.out.println(ex.getMessage());
}
}
Please help me out I seem to be confused on what kind of collection to use and how to go about it Thanks
You could create a method to read a file and put the data in an Array, but, if you are determined to use an Array you are going to have to create it at a fixed size b/c arrays are immutable in java
public class tmp {
public static void main(String[] args) throws FileNotFoundException {
//problem you have to create an array of fixed size
String[] array = new String[4];
readLines(array);
}
public static String[] readLines(String[] lines) throws FileNotFoundException {
//this counter can be printed to check the size of your array
int count = 0; // number of array elements with data
// Create a File class object linked to the name of the file to read
java.io.File myFile = new java.io.File("path/to/file.txt");
// Create a Scanner named infile to read the input stream from the file
Scanner infile = new Scanner(myFile);
/* This while loop reads lines of text into an array. it uses a Scanner class
* boolean function hasNextLine() to see if there another line in the file.
*/
while (infile.hasNextLine()) {
// read a line and put it in an array element
lines[count] = infile.nextLine();
count++; // increment the number of array elements with data
} // end while
infile.close();
return lines;
}
}
However, the preferred method is to use an ArrayList which is an object that uses dynamically resizing arrays as data is added. In other words, you don't need to worry about having different size text files.
public static void main(String[] args) throws IOException {
BufferedReader in = new BufferedReader(new FileReader("path/of/file.txt"));
String str;
ArrayList<String> list = new ArrayList<String>();
while ((str = in.readLine()) != null) {
list.add(str);
}
String[] stringArr = list.toArray(new String[0]);
A little about random access.
Classes like BufferedReader and FileInputStream use a sequential process of reading or writing data. RandomAccess, on the other hand, does exactly as the name implies, which is to permit non-sequential, random access to the contents of a file. However, Random access is typically used for other applications like reading and writing to zip files. Unless you have speed concerns I would recommend using the other classes.
public static void main(String[] args) throws FileNotFoundException {
BufferedReader in = new BufferedReader(new FileReader("src\\workshop7\\customers.txt"));
String str;
String names[];
List<String> firstName = new ArrayList();
List<String> lastName = new ArrayList();
try {
while ((str = in.readLine()) != null) {
names = str.split("\\s");
int count = 0;
do{
firstName.add(names[count]);
lastName.add(names[count+1]);
count = count + 2;
}while(count < names.length);
}
} catch (IOException e) {
e.printStackTrace();
}
// do whatever with firstName list here
System.out.println(firstName);
// do whatever with LastName list here
System.out.println(lastName);
}
Related
I am new at Java so please bear with me.
I need help for one of my assignments again. Now it involves FileI/O.
The task that I have to do is:
I have to read a .csv file. The values that's inside the file are:
Christopher Lee,54.0
Stanley Wright,90.5
Oliver Stewart,75.8
Jessica Chang,34.65
As the task said, I must store the contents on the file into two arrays. One for the names, and one for the test marks. I should read the file at least twice, once to check how many names are in the file and a couple more times to actually read the file (to get the names and marks). So basically, I should have an array to store the names as Strings, and an array to store the marks of the student as real numbers.
I should line up the arrays (e.g.students[0] should store the name of the first student and marks[0] should store the mark of the first student
After I stored the contents of the .csv file into an array I have to display a following menu to the user. If the user pressed 1, it should prompt the user to enter the name of a student. If the user pressed 2, the program should exit. If the name exists, it should display the test mark for the student entered. If the student does not exist then I must output a message indicating so to the user, yet the program should not end but return to the above menu.
This is my code so far:
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
String fileName = "file:///Documents/Java/marks_file.csv"; // Opens the file
String[] arrayString = new String[6]; // String length inside the file
int numLines, selection = 0;
double[] arrayReal = new double[6]; // Number length inside the file
numLines = getNumLines(fileName); // Gets the length of the file
readFile(arrayString, arrayReal, fileName);
// Selection menu
do
{
System.out.println("Select an option:");
System.out.println("1. Display mark");
System.out.println("2. Exit");
selection = sc.nextInt();
if (selection == 1)
{
System.out.println("Enter your full name");
{
// Do something
}
}
else if (selection == 2)
{
System.out.println("Goodbye");
}
}
while (selection == 1);
//System.out.println("Number of arrays: " + numLines);
}
// Method to get the length of the .csv file
public static int getNumLines(String fileName)
{
FileInputStream fileStrm = null;
InputStreamReader rdr;
BufferedReader bufRdr;
String line;
int lineNum = 0;
try
{
fileStrm = new FileInputStream(fileName);
rdr = new InputStreamReader(fileStrm);
bufRdr = new BufferedReader(rdr);
line = bufRdr.readLine();
while (line != null)
{
lineNum = lineNum + 1;
line = bufRdr.readLine();
}
fileStrm.close();
}
catch (IOException e)
{
try
{
if (fileStrm != null)
{
fileStrm.close();
}
}
catch (IOException ex2)
{
// Nothing to do
}
System.out.println("Error in file processing: " + e.getMessage());
}
return lineNum;
}
// Method to store the values to arrays
public static void readFile(String[] arrayString, double[] arrayReal, String fileName)
{
Scanner sc = new Scanner(System.in);
FileInputStream fileStrm = null;
InputStreamReader rdr;
BufferedReader bufRdr;
String line;
try
{
fileStrm = new FileInputStream(fileName);
rdr = new InputStreamReader(fileStrm);
bufRdr = new BufferedReader(rdr);
for (int i = 0; i < arrayString.length; i++)
{
line = bufRdr.readLine();
arrayString[i] = processString(line);
arrayReal[i] = processReal(line);
}
}
catch (IOException e)
{
try
{
if (fileStrm != null)
{
fileStrm.close();
}
}
catch (IOException ex2)
{
// Nothing to do
}
System.out.println("Error in file processing: " + e.getMessage());
}
}
// Stores the String lines to array
public static String processString(String line)
{
String string;
String[] lineArray = line.split(",");
return string = lineArray[0];
}
// Stores real number lines to array
public static double processReal(String line)
{
double real;
String[] lineArray = line.split(",");
return real = Double.parseDouble(lineArray[1]);
}
So far, I finished the "reading the file" part and processing the contents from a .csv file to an array.
I am not too sure how to prompt a user to search a string array from a .csv file. I tried looking at other sources, even at this website but I have no luck at all. I tried the Scanner.next() method but that doesn't work at all. Maybe I just missed something. Also, I am not sure if I did the "reading the file twice" right.
Am I on the right track? I am need of some guidance here
First of all I want to say that I'd use a Map instead of two arrays but I'll show you a solution using two arrays.
You were close to the solution. One of you problems is that scanner.next() only reads the input until the first whitespace. That's why you need to use scanner.nextLine(). This method reads the complete line. And the code could look something like that:
Solution with two arrays
Scanner sc = new Scanner(System.in);
System.out.print("Please enter name of student: ");
String name = sc.nextLine();
for(int i = 0; i < arrayString.length; i++){
if(name.equals(arrayString[i])) {
System.out.println(arrayReal[i]);
}
}
Solution with a HashMap
Initialize HashMap
HashMap<String, Double> hm = new HashMap<String, Double>();
Fill HashMap
hm.put("Christopher Lee", 54.0);
Print double value of student
System.out.print("Please enter name of student: ");
String name = sc.nextLine();
System.out.println(hm.get(name));
Instead of storing into arrays, I would rather tell you to pass the data to data into generic arraylist and then query the result using get() method.
You are making simple thing difficult.
Just use a HashMap with name as the keys and test-score as the values.
You open file
You read each line and translate each line to an entry of hash map
When a text is input to the console, you just get it from hash map, if existed return the value, if not then back to number 3
I am working in creating inverted index for list of words in java. Basically it creates a list for each word contains the document index that word appear on associated with frequency of word in that document, the desired output should be like this:
[word1:[FileNo:frequency],[FileNo:frequency],[FileNo:frequency],word2:[FileNo:frequency],[FileNo:frequency]...etc]
Here is the code:
package assigenment2;
import java.io.*;
import java.util.*;
public class invertedIndex {
public static Map<String, Map<Integer,Integer>> wordTodocumentMap;
public static BufferedReader buffer;
public static BufferedReader br;
public static BufferedReader reader;
public static List<String> files = new ArrayList<String>();
public static List<String>[] tokens;
public static void main(String[] args) throws IOException {
//read the token file and store the token in list
String tokensPath="/Users/Manal/Documents/workspace/Information Retrieval/tokens.txt";
int k=0;
String[] tokens = new String[8500];
String sCurrentLine;
try
{
FileReader fr=new FileReader(tokensPath);
BufferedReader br= new BufferedReader(fr);
while ((sCurrentLine = br.readLine()) != null)
{
tokens[k]=sCurrentLine;
k++;
}
System.out.println("the number of token are:"+k+" words");
br.close();
}
catch(Exception ex)
{System.out.println(ex);}
Until there it works correctly, I believe that the problem is in the manipulating the nested map in the following part:
TreeMap<Integer,Integer> documentToCount = new TreeMap<Integer,Integer>();
//read files
System.out.print("Enter the path of files you want to process:\n");
Scanner InputPath = new Scanner(System.in);
String cranfield = InputPath.nextLine();
File cranfieldFiles = new File(cranfield);
for (File file: cranfieldFiles.listFiles())
{
int fileno = files.indexOf(file.getPath());
if (fileno == -1) //the current file isn't in the files list \
{
files.add(file.getPath());// add file to the files list
fileno = files.size() - 1;//the index of file will start from 0 to size-1
}
int frequency = 0;
BufferedReader reader = new BufferedReader(new FileReader(file));
for (String line = reader.readLine(); line != null; line = reader.readLine())
{
for (String _word : line.split(" "))
{
String word = _word.toLowerCase();
if (Arrays.asList(tokens).contains(word))
if (wordTodocumentMap.get(word) == null)//check whether word is new word
{
documentToCount = new TreeMap<Integer,Integer>();
wordTodocumentMap.put(word, documentToCount);
}
documentToCount.put(fileno, frequency+1);//add the location and frequency
}
}
}
reader.close();
}
}
The error I get is:
Exception in thread "main" java.lang.NullPointerException
at assigenment2.invertedIndex.main(invertedIndex.java:65)
You’re never instantiating wordTodocumentMap, so it remains null throughout. Therefore the line if (wordTodocumentMap.get(word) == null)//check whether word is new word throws a NullPointerException when you do .get(), that is, before you have anything to compare to null. One possible solution is to instantiate the map in the declaration:
public static Map<String, Map<Integer,Integer>> wordTodocumentMap = new HashMap<>();
There may be other problems in your code, but this should get you a step further.
I am trying to segregate my data into multiple array list, so that I can use them later-on in my code. But I am not able to put my data in array list.
My code is about segregating the data into three array list of different Subjects (Example:Physics,chemistry) as per various filters, which you will find in my code.
Input data file:
1|150|20150328|20150406|Physics|1600|1600|2|68|92
2|152|20150328|20150406|Physics|1600|1500|2|68|89
3|153|20150328|20150406|Physics|1600|1500|2|68|60
4|155|20150328|20150406|Physics|1600|1600|2|68|72
5|161|20150328|20150406|Chemistry|1600|1600|2|68|77
Here's my code:
Public Class filter{
public static void main(String args[])
BufferedReader in= null;
BufferedWriter out= null;
String in_line;
String PrevRollNo= "";
int PrevDate= 0;
ArrayList<transaction> PhysicsList= new ArrayList<transaction>();
ArrayList<transaction> scList= new ArrayList<transaction>();
ArrayList<transaction> Chemistry= new ArrayList<transaction>();
try{
in = new BufferedReader(new FileReader(Path for input file));
File out_file= new File(Path for output file);
if(!out_file.exists())
{
(!out_file.createNewFile();
}
FileWriter fw=new FileWriter(out_file);
out= new BufferedWriter(fw);
while ((in_line=in.readline())!=null)
{
Transaction transact=new Transaction(in_line);
if(transact.RollNo.equals(PrevRollNo))
{
if(transact.subject.equals("Physics")&& transact.Prs_Date= PrevDate
{
PhysicsList.add(transact);
}
else if(transact.subject.equals("Physics")&&transact.wk_date != PrevDate}
Iterator<Transaction> it;
if(!transact.RoomNo.equals("102")&&!transact.lcl_RoomNo.equals("102");
{
it= scList.iterator();
while(it.hasnext())
{
Transaction sc= it.next();
if(sc.lcl_RoomNo.equals(transact.RoomNo) && sc.l1 equals(tansact.l1) && sc.l2 equals(transact.l2)
if(sc.marks==transact.marks)
{
transact.srsfound= true;
}
else
{
System.out.print.ln( "not found");
}
scList.remove(sc))
out.write(in_line);
break;
}}}}
Static Class Transaction
{
Public String RollNo, Subject, RoomNo, lcl_RoomNo, l1, l2;
Public int wk_date, prs_date;
Public double marks , amt;
Public boolean srcfound, tgtfound;
Public Transaction(String in_line)
{
String [] SplitData= in_line.split("\\|");
RollNo = SplitData[1];
Subject = SplitData[4]
RoomNo = SplitData[5];
lcl_RoomNo = SplitData[6];
l1 = SplitData[7];
l2 = SplitData[8];
wk_date = SplitData[3];
prs_date = SplitData[2];
marks = Double.parsedouble(SplitData[9]);
amt = Double.parsedouble(SplitData[]);
srcfound = false;
tgtfound = false;
}
Kindly help with your expertise.
Use Java 8 NIO and Streams. It will ease the job.
Files.lines(Paths.get("fileName.txt")).map(line -> {
String[] tokens = line.split("|");
//tokens contains individual elements of each line. Add your grouping logic on tokens array
}
I agree with the other answer in some ways. NIO should be used, it makes it a lot easier. However, I would avoid streams and instead use the readAllLines method like so:
try{
List<String> filecontents = new String(Files.readAllLines(file.toPath()); //file is the object to read from.
for(int i = 0; i < filecontents.size(); i++){
String line = lines.get(i);
//New code starts here
if(!line.contains("|") continue; //Ignore that line
//New code ends here
String[] array = line.split("|");
ArrayList<String> list = new ArrayList<String>();
for(int a = 0; a < array.length; a++){
String part = array[a];
list.add(part);
}
Transaction t = new Transaction(line);
if(line.contains("Physics") PlysicsList.add(t);
else if(line.contains("Chemistry") Chemistry.add(t);
else{ //Do nothing}
}
}catch(IOException e){
e.printStackTrace();
}
EDIT: I added a check in there. The reason the first and last lines may not be working is if the lines that are being parsed are not being parsed properly. See if this fixes your issue
I am trying to figure out how to make a program that reads data from a text file, and fills a Jtable with it, I will need to be able to search the table, and do some calculations with the numbers.
A row in the text file would contain:
name, country, gender, age, weight
The number of rows is unknown (I need to count the number of rows).
This is what I tried, but it seems to crash. I need to count the # of rows, and then fill the array with the content from the rows.
package Jone;
import java.io.*;
import java.util.*;
public class Jone {
public static void main (String [] args)throws IOException{
int rows = 0;
Scanner file = new Scanner (new File("data.txt"));
while (file.hasNextLine()){rows++;}
Object[][] data = new Object[rows][5];
System.out.print(rows);
file.nextLine();
for(int i = 0;i<rows;i++)
{
String str = file.nextLine();
String[] tokens= str.split(",");
for (int j = 0;j<5;j++)
{
data[i][j] = tokens[j];
System.out.print(data[i][j]);
System.out.print(" ");
}
}
file.close();
}
}
change your code as follows
package Jone;
import java.io.*;
import java.util.*;
public class Jone {
public static void main (String [] args)throws IOException{
try{
int rows = 0;
Scanner file = new Scanner (new File("data.txt"));
while (file.hasNextLine())
{
rows++;
file.nextLine();
}
file = new Scanner (new File("data.txt"));
System.out.println(rows);
Object[][] data = new Object[rows][5];
for(int i = 0;i<rows;i++)
{
String str = file.nextLine();
String[] tokens= str.split(",");
for (int j = 0;j<5;j++)
{
data[i][j] = tokens[j];
System.out.print(data[i][j]);
System.out.print(" ");
}
}
file.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
You create an array with 0 rows and then you try to access the empty array dimension.
Also I suppose you should reset the pointer of the scanner after counting the rows.
ArrayList should be more useful for your goal.
class Person {
String name, country, gender;
int age;
double weight;
public Person(String n, String c, String g, int a, double w) {
name = n;
country = c;
gender = g;
age = a;
weight = w;
}
}
Would properly model your data better when you are extracting from the file (I took a guess at Person but call it what you will). We then use ArrayList like so:
public static void main (String[] args) throws IOException {
ArrayList<Person> people = new ArrayList<Person>();
Scanner file = new Scanner (new File("data.txt"));
while (file.hasNextLine()) {
String str = file.nextLine();
String[] tokens= str.split(",");
people.add(new Person(tokens[0], tokens[1], tokens[2],
Integer.parseInt(tokens[3], Double.parseDouble(tokens[4]))));
}
file.close();
Person[] arrayPeople = people.toArray();
}
ArrayLists are far more powerful than arrays as you can perform all sorts of operations on them like sorts and searches and of course you don't have to worry about their initial size because they just grow as you add new elements.
Maroun is right, you really need to use some Collections to help you with that :
public static void main(String[] args) throws Exception {
List<String[]> lines = readFiles(new File("data.txt"));
String[][] data = lines.toArray(new String[0][]);
}
public static List<String[]> readFiles(File file) {
List<String[]> data = new LinkedList<>();
Scanner scanner = null;
try {
scanner = new Scanner(file);
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
String[] tokens = line.split(",");
data.add(tokens);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} finally {
scanner.close();
}
return data;
}
Note that you can use some third party libraries like Commons IO to read the file's lines :
List<String> lines = org.apache.commons.io.FileUtils.readLines(new File("data.txt"));)
Less code = less bugs!
Hope it helps
Move this line
Object[][] data = new Object[rows][5];
below
System.out.print(rows);
But as per answers above, we suggest change the code to use array lists if possible.
Here is my code:
import java.util.Scanner;
import java.io.*;
import java.util.ArrayList;
public class Filter{
Message myMessage;
Scanner input;
Scanner input2;
String sender;
String subject;
String emailMIN;
String line;
String line2;
ArrayList<String> blacklist = new ArrayList<String>();
ArrayList<String> keywords = new ArrayList<String>();
ArrayList<String> subjectWords = new ArrayList<String>();
ArrayList<String> emails = new ArrayList<String>();
//String[] lines;
File SpamMessage;
File inFile;
File inFile2;
File tempFile;
String[] lines;
public Filter(Message m,String blacklistFile, String keywordFile, String Spam)throws IOException{
inFile = new File(blacklistFile);
inFile2 = new File(keywordFile);
input = new Scanner (inFile);
input2 = new Scanner (inFile2);
myMessage =m;
SpamMessage=new File(Spam);
}
public void filter() throws IOException{
PrintWriter output = new PrintWriter(SpamMessage);
while(input.hasNextLine()){
line = input.nextLine();
//System.out.println(line);
if(line!=null)
blacklist.add(line);
}
while(input2.hasNextLine()){
line2 = input2.nextLine();
//System.out.println(line2);
if(line!=null)
keywords.add(line2);
}
emails=myMessage.getEmails();
// System.out.println(emails.size() + emails.get(1));
for(int i = 0; i < emails.size(); i++){
// boolean isSpam = false;
lines = emails.get(i).split("\n");
// System.out.println(lines[5] + lines[7]);
sender = lines[2].substring(lines[2].indexOf('<'), lines[2].indexOf('>'));
//` System.out.println(sender);
emailMIN = lines[6].substring(lines[6].indexOf('<'), lines[6].indexOf('>'));
// System.out.println(emailMIN);
for(int j =0; j<lines.length; j++)
{
if(j==2)
{
for(String blacklist2: blacklist)
{
// System.out.println(blacklist2);
if(lines[j].contains(blacklist2))
{
output.println(emailMIN);
}
// output.close();
}
}
if(j==5 || j>=7)
{
// System.out.println(keywords.size());
for(String keywords2: keywords)
{
// System.out.println(keywords2);
if(lines[j].contains(keywords2))
{
output.println(emailMIN);
}
// output.close();
}
}
//addKeywords();
}
}
output.close();
addKeywords();
}
public void addKeywords() throws IOException
{
tempFile = new File("tempFile.txt");
PrintWriter pw = new PrintWriter(new FileWriter(tempFile));
for(int i=0; i<lines.length; i++)
{
if(i==5){
String[] words = lines[i].split(" ");
for(String word: words){
if(word.length()>=6){
subjectWords.add(word +"\n");
//System.out.println(subjectWords);
}
}
keywords.addAll(subjectWords);
pw.println(keywords);
}
}
pw.close();
if (!inFile2.delete()) {
//System.out.println("Could not delete file");
return;
}
// Rename the new file to the filename the original file had.
if (!tempFile.renameTo(inFile2)){
//System.out.println("Could not rename file");
}
}
}
I'm trying to update the list of words in the keywords txt file right now it does update it but it puts it in the format [generic, pharmacy, little, inside]
Which is wrong because then if I run my code again it is searching if the file contains [generic, pharmacy, little, inside] and I need it to search for every word not the plus a comma or brace. So basically I want it to copy the words in a list format like this
generic
pharmacy
little
inside
That way it searches for each individual word. I figured out how to do this part. Now, how do I add the senders to a different text file? Also is there a way to modify this so it doesn't add the same keywords twice? Thanks
It is because you are writing an array to the file which causes the toString method of it to be called. Write every single item instead.
Instead of pw.println(keywords);
Do:
for (String keyword : keywords)
{
pw.println(keyword.trim());
}
Or, if every word contains \n already, this should work
for (String keyword : keywords)
{
pw.print(keyword);
}
Instead of doing:
pw.println(keywords);
you should instead loop through the array and add each line individually.
for(int i = 0; i < keywords.length; i++) {
pw.println(keywords[i]);
}
That was because you are printing an ArrayList object. In your code, keywords is instance of the List and which would you give you an output of [aa,bb] . More over you would get duplicate words since these list instance are class variables, and printed inside a loop
keywords.addAll(subjectWords);
pw.println(keywords);
Either you can loop around keywords outside the for loop or print the word before adding to list.