I'm working on a program that will go through a list of records (IDs and Tickets) and parse them into two list respectively. It will also cross search the lists to see which IDs have a corresponding ticket based on names. Here is a link to an earlier version: here
Now, I've been rewritting with the help of some C# code from a coworker, but I'm having trouble with a parsing method. Here is the C# version:
public void parseLine(string _line)
{
if(string.IsNullOrWhiteSpace(_line)){ return;}
code = _line.Substring(0, 3);
ticketID = _line.Substring(3, 10);
string tmp = _line.Substring(13).Trim();
//get the first and last name
string [] tmp1 = tmp.Split(",".ToCharArray());
if(!(tmp1.Length > 1))
{
throw new Exception("unable to get the first and last name");
}
lastname = tmp1[0];
firstname = tmp1[1].Trim();
}
Here is my Java version:
public void parseLine(String line) throws Exception {
// code will store Ticket code *Alpha ticketId will store 10
// *digit code
code = line.substring(0, 3);
ticketId = line.substring(3, 10);
// tmp will store everything afterthe first 13 characters of
// line and trim the name(s)
String tmp = line.substring(13).trim();
// tmp1 array
String[] tmp1 = tmp.split(".*,.*");
if (tmp1.length > 1) {
throw new Exception("UNABLE TO GET NAME");
}
last = tmp1[0];
first = tmp1[1].trim();
}
This is in a seperate class, that will model the people with tickets. My main class(so far) which invokes the actual parseLine method is as follows:
public class ParkingTickets {
public static void main(String[] args) throws
FileNotFoundException, Exception {
ArrayList<TicketPeople> tickets = new ArrayList<>();
HashMap<String, List<SbPeople>> people = new HashMap<>();
File srcFile = new File("source.txt");
Scanner myScanner = new Scanner(srcFile);
while (myScanner.hasNextLine()) {
String line = myScanner.nextLine();
//System.out.println(line);
if (line.matches("^\\p{Alpha}.*$")) {
//System.out.printf("Ticket: %s%n", line);
TicketPeople t = new TicketPeople();
t.parseLine(line);
tickets.add(t);
}
myScanner.close();
}
}
}
the compiler points at the if statement in the parseLine method, and obviously the parseLine method in main class, when I tried stepping through that sepcifiv line, I see that it's starts parsing the the data from the source file but something is off. From the documentation the error means: Thrown to indicate that an array has been accessed with an illegal index. The index is either negative or greater than or equal to the size of the array.
I used an ArrayList for the ticket list and from what I understand it is a dynamic list that does not need to be set with a specific index size. I'm still learning and am having trouble understanding this exception. I would greatly appreciate any help.
Your call to split() in Java, doesn't match the split() from C#.
// String[] tmp1 = tmp.split(".*,.*");
String[] tmp1 = tmp.split(","); // <-- ",".
also, your check logic seems to have been reversed. But, I would suggest
if (tmp1.length != 2) {
throw new Exception("UNABLE TO GET NAME");
}
1) In C# it is Substring(int startIndex, int length). In java String substring(int startindex, int endindex).
2)The java code has also changed the exception logic. In C# code ther eis a not if(!(tmp1.Length > 1)), whereas in java code, if (tmp1.length > 1)
Related
I am trying to store the contents from a file into an array String retval[] , copy that array to String[] fed() and pass the array into main. So far, the array stores and copies but the array method returns null in main String []feed; feed=uio.fed();.
UserIO.java
package fileio;
import classes.*;
import java.util.*;
import java.lang.*;
import java.io.*;
public class UserIO
{
public String search (String line0)
{
String line;
try
{
FileInputStream ufin = new FileInputStream("E:\\3rd sem\\OOP\\Projects\\New folder (2)\\BOOK LIBRARY\\fileio\\user.txt");
Scanner sc = new Scanner(ufin);
while (sc.hasNextLine())
{
line=sc.nextLine();
if(line.contains(line0))
{
String retval[]= line.split(" ");
feed= new String[retval.length];
for (String s: retval)
{
System.out.println("\t\t\tFrom retval:"+s);
}
for (int n=0;n<retval.length;n++)
{
feed[n]=retval[n];
System.out.println("\tFrom feed:"+feed[n]);
}
}
}
}
catch(IOException ioe)
{
ioe.printStackTrace();
}
return line0;
}
public static String [] feed;
public static String[] fed()
{
String [] fd;
fd= new String[feed.length];
for (int n=0;n<feed.length;n++)
{
fd[n]=feed[n];
System.out.println("From fd:"+fd[n]);
}
return fd;
}
}
Down below is the main method
Execute.java
import java.lang.*;
import java.util.*;
import classes.*;
import fileio.*;
public class Execute
{
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
String adminusername = "a";
String adminpassword = "p";
String readerusername = "r";
String readerpassword = "p";
String nreaderusername;
String nreaderpassword;
Library b = new Library();
UserFileReadWriteDemo ufrwd = new UserFileReadWriteDemo();
UserIO uio = new UserIO();
System.out.println("enter id ");
String id = sc.next();
uio.search(id);
try
{
String []feed;
feed=uio.fed();
//uio.fed()=feed.clone;
for(int s=0;s<feed.length;s+=5)
{
String nid00= null;
feed[0+s]= nid00;
String name00=null;
feed[1+s]= name00;
String age00= null;
feed[2+s]= age00;
String uname00= null;
feed[3+s]= uname00;
String upassword00= null;
feed[4+s]= upassword00;
Reader c00 = new Reader(nid00, name00, age00,uname00,upassword00);
b.insertReader(c00);
System.out.println(" In main"+feed[s]);
}
}
catch (NullPointerException n)
{
n.printStackTrace();
}
}
Your code is a little bit difficult to read and also has a lot of unnecessary repetitions, for example method fed has no role, why not call search and make search return an array with the found elements? You are making search return the line you are searching for which you already know when you gave search that argument in the first place, it is just returning a useless value.
Also it is difficult to understand what search actually does, from what i see it finds the last occurrence of line0 in the file, because it continues to iterate over lines and every time it finds line0 it will create new feed array in UserIO and eliminate all the previous array it found, and will return when all file has been read. If this is your intention then this is not the right way to do it as it is inefficient, because you keep creating arrays that will be discarded. If your intention is the last occurrence of line0 then you can just assign a found line to a String variable and when the iteration finishes just split and return that array as it will be the last occurrence of line0 in the file.
As i see it the only way that fed will return null is if there is no line with line0 in the file because search initializes the array if it finds line0 at least once in the file, this way feed will be an uninitialized array which will be a null pointer.
These lines has no meaning:
String nid00= null;
feed[0+s]= nid00;
String name00=null;
feed[1+s]= name00;
String age00= null;
feed[2+s]= age00;
String uname00= null;
feed[3+s]= uname00;
String upassword00= null;
feed[4+s]= upassword00;
I think you meant nid00 = feed[0+s] and so on, because the way you wrote the assignment to nid00 and the other variables will be always null which will be useless.
Also when you copy arrays try to use Arrays.copyOf methods or System.arraycopy they save you writing several lines and also they are more efficient, read about them in the documentation.
And the last thing, it is not useful to catch nullpointer exception if you wrote your code, in general you must know what your methods do and if there is a nullpointer exception in something you wrote then there is something wrong in your code, if for example a method you wrote returns null then you must know about the possibility of a null return and handle that possible return, this way it will be easier for you to read your code and use it and also for others who use your code.
The nullpointer you are getting is because you trying to get the length of an uninitialized feed inside fed method, you must be very careful.
This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 5 years ago.
I've created a class called Human that works properly, it takes 2 arguments, age and name, to create a human.
To create a Human with command line arguments, I want to write
java Filename -H "Anna" 25
And it should create a Human with thatname="Anna", and thatage=25, where 25 is an int.
The code I've written is creating a list called Argument, and iterating through it to find -H. I need to do this because I'm going to be using this to create different classes later. I just need help with the syntax on the lines where I've written thename=, and theage=, because I don't know how to get the next item in list, and next-next item in list.
public static void main(String[] args) {
ArrayList<String> Argument = new ArrayList<String>();
for (String item: args) {
Argument.add(item);
}
for (String item2: Argument) {
if (item2 == "-H") {
thatname = Argument.get(item2+1)
thatage = Argument.get(item2+2)
Human person = new Human(thatname,thatage);
System.out.println(person);
}
Why not just loop the args?
for ( int i = 0; i < args.length; i++ ) }
if (args[i].equals("-H")) {
i++;
thatName = args[i];
i++;
thatAge = args[i];
}
}
You should add some code to catch if one does not follow the rules you have set. Probably not enough arguments or other things humans do at the keyboard...
thatname = Argument.get(Argument.indexOf(item2)+1);
thatage = Argument.get(Argument.indexOf(item2)+2);
OR you know that 1st element is -H, 2nd element is name and 3rd is age, so you can use below code directly
thatname = Argument.get(1);
thatage = Integer.parseInt(Argument.get(2));
Your code have some problems, let me explain them to you for your assistance.
You cannot compare Strings with == you have to use equals method
in the String to compare between two Strings.
You have to use this for loop for(int i = 0; i < Argument.size();
i++) syntax so that you can iterate from zero to the number of
items in the list.
get method in ArrayList take the index as parameter and return the value at that index.
You can add i += 2 to skip the next two iterations which will
return the name and age value of the human. (It is optional)
Here is the working code:
public static void main(String[] args) {
ArrayList<String> Argument = new ArrayList<String>();
for (String item: args) {
Argument.add(item);
}
String currentItem;
for (int i = 0; i < Argument.size(); i++) { // it will iterate through all items
currentItem = Argument.get(i); // getting the value with index;
if (currentItem.equals("-H")) {
String thatname = Argument.get(i+1);
String thatage = Argument.get(i+2);
i += 2; // Skipping 2 iterations of for loop which have name and age human.
Human person = new Human(thatname,thatage);
System.out.println(person);
}
}
}
You cannot iterate the list using String. When iterating a list you required a index number like list.get(indexNumber);
public static void main(String[] args) {
ArrayList<String> Argument = new ArrayList<String>();
for (String item: args) {
Argument.add(item);
}
for (int i=0;i<args.length;i++) {
if (args[i].trim().equals("-H")) {
i++;
thatname = Argument.get(i);
i++;
thatage = Argument.get(i);
Human person = new Human(thatname,thatage);
System.out.println(person.getName()+" "+person.getAge());
}
Why using array list when you can directly use args? and while you're having only two parameters don't use a for loop access them direclty.
One thing you should know is that String is an object in java so comparing two Strings with == sign will return false even if they have same value (== will compare the id of the object), you should use .equale() function to compare the value of the object.
Check out this code :
public static void main(String[] args) {
if(args.length>0)
{
try{
if (args[0].equals("-H")) {
Human person = new Human( args[1],args[2]);
System.out.println(person);
}
}catch(ArrayIndexOutOfBoundsException exception) {
System.out.println("error with parameters");
}
}else
System.out.println("No command");
}
I am working on a project for school and things are going well until i tried to perform a merge sort on my ArrayList.
It will run but then it errors out. The first error of many is Exception in thread "main" java.lang.StackOverflowError.
I have looked over the code and cant find out why the error is occurring.
It does give me a location ( line 74:first_half = mergeSort(first_half); ) but i don't see the issue.
public static void main(String[] args) throws IOException {
// URL url = new
// URL("https://www.cs.uoregon.edu/Classes/15F/cis212/assignments/phonebook.txt");
FileReader fileReader = new FileReader("TestSort.txt");
BufferedReader bufferReader = new BufferedReader(fileReader);
String entry = bufferReader.readLine();
// Scanner s = new Scanner(url.openStream());
// int count = 0;
while (entry != null) {
// String person = s.nextLine();
String phoneNum = entry.substring(0, 7);
String name = entry.substring(9);
PhonebookEntry newentry = new PhonebookEntry(name, phoneNum);
phoneBook.add(newentry);
entry = bufferReader.readLine();
}
// ********************Selection
// Sort*************************************
ArrayList<PhonebookEntry> sortList = new ArrayList<PhonebookEntry>(phoneBook);
for (int min = 0; min < sortList.size(); min++) {
for (int i = min; i < sortList.size(); i++) {
int res = sortList.get(min).getName().compareTo(sortList.get(i).getName());
if (res > 0) {
PhonebookEntry temp = sortList.get(i);
sortList.set(i, sortList.get(min));
sortList.set(min, temp);
}
}
}
for (PhonebookEntry sortentry : sortList) {
System.out.println(sortentry);
}
System.out.println(mergeSort(mergeSortList));
}
// *****************************merge sort******************************************
static int mergecounter = 0;
static ArrayList<PhonebookEntry> mergeSortList = new ArrayList<PhonebookEntry>(appMain.phoneBook);
public static ArrayList<PhonebookEntry> mergeSort(ArrayList<PhonebookEntry> mergeSortLists) {
if (mergeSortLists.size() == 1) {
return mergeSortLists;
}
int firstHalf = mergeSortLists.size() % 2 == 0 ? mergeSortLists.size() / 2 : mergeSortLists.size() / 2 + 1;
ArrayList<PhonebookEntry> first_half = new ArrayList<PhonebookEntry>(mergeSortLists.subList(0, firstHalf));
ArrayList<PhonebookEntry> mergeSortHalf2 = new ArrayList<PhonebookEntry>(
mergeSortLists.subList(first_half.size(), mergeSortLists.size()));
System.out.println(++mergecounter);
first_half = mergeSort(first_half);
mergeSortHalf2 = mergeSort(mergeSortHalf2);
return merge(first_half, mergeSortHalf2);
}
public static ArrayList<PhonebookEntry> merge(ArrayList<PhonebookEntry> first_half,
ArrayList<PhonebookEntry> mergeSortHalf2) {
ArrayList<PhonebookEntry> returnMerge = new ArrayList<PhonebookEntry>();
while (first_half.size() > 0 && mergeSortHalf2.size() > 0) {
if (first_half.get(0).getName().compareTo(mergeSortHalf2.get(0).getName()) > 0) {
returnMerge.add(mergeSortHalf2.get(0));
mergeSortHalf2.remove(0);
}
else {
returnMerge.add(first_half.get(0));
first_half.remove(first_half.get(0));
}
}
while (first_half.size() > 0) {
returnMerge.add(first_half.get(0));
first_half.remove(first_half.get(0));
}
while (mergeSortHalf2.size() > 0) {
returnMerge.add(mergeSortHalf2.get(0));
mergeSortHalf2.remove(mergeSortHalf2.get(0));
}
return returnMerge;
}
}
My opinion there is no error in code.
How so sure?
I ran you code in my environment and its executed without any error.
With the text file i found at https://www.cs.uoregon.edu/Classes/15F/cis212/assignments/phonebook.txt As input
and done a simple implementation for PhonebookEntry
Then why is this error?
First off all try to understand the error, I mean why StackOverflowError occur. As there are lots of I am not going to explain this
But please read the top answer of this two thread and i am sure you will know why this happen.
Thread 1: What is a StackOverflowError?
Thread 2: What actually causes a Stack Overflow error?
If you read those I hope you understand the summury is You Ran Out Of Memory.
Then why I didnt got that error: Possible reason is
In my environment I configured the jvm to run with a higher memory 1024m to 1556m (as eclipse parameter)
Now lets analyze your case with solution:
Input: you have big input here ( 50,000 )
To check you code try to shorten the input and test.
You have executed two algorithm in a sigle method over this big Input:
When a method execute all its varibles stay in the memory untill it complete its execution.
so when you are calling merge sort all previouly user vairables and others stay in the memory which can contribute to this situation
Now if you use separated method and call them from the main method like write an method for selection sort, all its used varible will go out of scope
and possibly be free (if GC collect them) after the selection sort is over.
So write two separated method for reading input file and selection sort.
And Please Please close() those FileReader and BufferedReader.
Get out of those static mehtod . Make them non static create and object of the class and call them from main method
So its all about code optimization
And also you can just increase the memory for jvm and test by doing like this java -Xmx1556m -Xms1024m when ruining the app in command line
BTW, Thanks for asking this this question its gives me something to think about
I'm trying to create a simple method. Basically, I want this method (called "returnIndex") to return the word at the ArrayList index number the user types in.
Example:
If the user types in "1", is should return whatever String is at index 1 in the ArrayList.
This is what I have so far:
public void returnIndex ()
{
Scanner in = new Scanner (System.in)
while (in.hasNextLine())
{
if (in.equals(1))
{
//return item at that index
}
}
}
I'm just not sure how to say "return the item at that index" in Java. Of course, I'll have to make the code work with any other number, not just '1'. But for now, I'm focusing on '1'. Not even sure if the in.equals(1) part is even 100% right.
My apologies if this question seems a little elementary. I'm still working on my Java. Just hints please, no complete answers. Thank you very much.
public String returnIndex(Scanner in, List<String> list) {
return list.get(in.nextInt());
}
Don't create new Scanners as it can cause subtle problems. Instead, create only one and keep using it. That means you should pass it into this function.
There's no need to use ArrayList when List will do (as it will here).
You need to make the function return String, not void, if you want it to return a String.
public static void main(String[] args) {
List<String> values = new ArrayList<String>();
values.add("One");
values.add("Two");
values.add("Three");
String result = getStringAtIndex(values);
System.out.println("The result:" + result);
}
public static String getStringAtIndex(List<String> list) {
Scanner scanner = new Scanner(System.in);
int index = 0;
index = scanner.nextInt();
return list.get(index-1);
}
First of all, id like to thank this fourm, as I am finding myself quickly improving through all the material on this forum and all the help different members have been giving me. So this is just a big thank you for all of that. As for my question, I've been experimenting around with input out and wanted to see if this logic would work. I am trying to get the appropriate things in their appropriate array, and wanted to see if this logic would do it. Currently (and for a while) I wont be in a place where I can access any Virtual IDE effectively so all this was kinda done on the fly using notepad, word etc. *So don't be to hard on my syntax. What I am mostly concerned about is the logic (if it would work) and to a lesser mistake any major mistakes in code.*
Thanks alot.
So basically, the text file goes like this. Title, one line of space, then name, age and wage and the separator is the #. Then right below that, name, age and wage the separator bring # etc etc.
(pretend there was no line spaces between Bobby, Sandy, Roger, Eric and David..so pretend in the txt file they are right under each other, but there is a gap in between information and bobby.
Information
Bobby#24#5.75
Sandy #19#10.22
Roger #27#6.73
Eric#31#8.99
David#12#3.50**
Here is the logic i've come up with.
public class Practice {
public static void main(String[] args) throws Exception {
String Name [] = new String [5];
int Age [] = new int [5] ;
double Wage [] = new double [5];
String Blank [] = new String [5];
FileReader inputfile = new FileReader (new File(info.txt));
BufferedReader InputBuffer = new BufferedReader (inputfile);
String Title = InputBuffer.readline (); // to get the title
int count = 0;
while (InputBuffer.readline() = null) { // this while loop grabs the blank under the title
Blank [count] = count;
}
int i = 0;
while (InputBuffer.readline() !=null) {
String Getter = InputBuffer.readline (); // reads line
String splitup= Getter.split(#); // splits it
Name [i] = splitup[i]; // puts name in this array
Age [i] = splitup([i] + 1); // age in this array
Wage [i] = splitup([i] + 2); // wage in this array
}
InputBuffer.close();
}
}
Would this logic work for storing the title in the title String, the Blank line under the Blank Array, the name under the name array, age under the age array and the wage under the wage array??
Thanks alot.
P.S: Mostly concerned about the last while loop, I want to know if it will put the name in the name array, the age in the age array and the wage in the wage array.
First of all, you only need one while-loop. I don't understand why you have two, especially since the conditional in the first is nonsensical ( InputBuffer.readline() = null ).
Your loop would look something like this:
boolean isTitleParsed = false;
String title;
String line;
while ( (line = inputBuffer.readLine()) != null ) {
if (!isTitleParsed) {
// this is the title
title = line;
isTitleParsed = true;
} else if (line.isEmpty()) {
// this is a blank line; logic for dealing with blank lines here
...
} else {
// this is actual person data
String[] personData = line.split("#");
if (personData != null && personData.length == 3) {
String name = personData[0];
String age = personData[1];
String wage = personData[2];
...
}
...
}
}
Secondly, I think using arrays is entirely the wrong way to go. Like #AVD mentioned in his comment on the OP, List<T> and a POJO is probably a much better solution -- and much more extensible.
And finally: no, as you've written it, your second loop will not successfully save the name, age, and wage to the arrays. You never increment i and the syntax splitup([i] + 1) is just wrong. (You probably meant splitup[i+1].)
Using Arrays
If you're really stuck on using arrays to save your data, you'd have to do in something like this:
String[] names = new String[5];
String[] ages = new String[5];
String[] wages = new String[5];
...
int index = 0;
while ( (line = inputBuffer.readLine()) != null && index < 5) {
if (!isTitleParsed) {
...
} else if (line.isEmpty()) {
...
} else {
// this is actual person data
String[] personData = line.split("#");
if (personData != null && personData.length == 3) {
String name = personData[0];
String age = personData[1];
String wage = personData[2];
names[index] = name;
ages[index] = age;
wages[index] = wage;
index++;
} else {
System.err.println("Line " + line + " is malformed and was not saved.");
}
...
}
}
Notice that index is instantiated at 0, but is incremented every time we save something to the arrays. This way names[0] will hold the first name, names[1] will hold the second, and so on.
Notice also that we save a given record's name, age, and wage all at the same index. So we could expect names[0] to hold "Bobby", ages[0] to hold "24", and wages[0] to hold "5.75" -- all of which are related to the same record.
Finally, the condition in the while loop has been amended to be (line = inputBuffer.readLine()) != null && index < 5. This means we'll keep looping through the lines of the file until we either run out of lines (the file ends) or our index becomes greater than 5, which is the size at which we instantiated the array. This is one reason why arrays are such a bad structure to hold this data: you have to know exactly how many records you have in your file, and you may end up not filling them all the way (you allocated too much space) or not saving some records because you have no more room to store them.
Using POJOs
A much better way to save the data would be to use a POJO -- a Plain Old Java Object. This kind of object is pretty much a "data holder" object.
In your case, it would be something like this:
public class PersonData {
private String name;
private String wage;
private String age;
public PersonData() {
this(null, null, null);
}
public PersonData(String name, String wage, String age) {
this.name = name;
this.wage = wage;
this.age = age;
}
// ... getters and setters here
}
In your code, you'd replace your arrays with a List structure of PersonData objects:
List<PersonData> records = new ArrayList<PersonData>();
And in your while loop, you'd save into these objects instead of into the arrays:
// in the else in the while loop:
String[] data = line.split("#");
if (data != null && data.length == 3) {
PersonData record = new PersonData(data[0], data[1], data[2]);
records.add(record);
} else {
// error handling for malformed line
}
Now if you wanted to get data for a particular record, you'd just need to extract the PersonData object from your records list and query it:
// assuming the first record we scraped was "Bobby#24#5.75"
PersonData person = records.get(0);
person.getName(); // returns "Bobby"
person.getAge(); // returns 24
person.getWage(); // returns 5.75
Since we're using a List and not an array, we don't have to worry about knowing exactly how many records there are in the file, and we don't run the risk of losing information because we don't have anywhere to store it.
This way we can also know for certain that a name, age, and wage are all related to the same record, whereas before we were just hoping that, say, all records at index 0 in the arrays were related to the same person.
Also, if you add additional data to the records -- for example, name#age#wage#favorite food -- all you have to do is add a new field to the PersonData object and add a line in your parsing method to add that data to the object. If you were using arrays, you'd need to add a new array, and so on.
It's also much easier to create logic if, say, you have a row that only has a name or that missing a wage, and so on -- so that you're actually able to save the data in some meaningful fashion.
If you want to make good progress in Java or any OOP Language for that matter you should always approach a problem in a Object Oriented Manner.
For the problem at hand you should always consider a class to store the Person Info rather than using associative arrays.
class PersonInfo {
PersonInfo(String name,int age,float wage) {
this.name = name;
this.age = age;
this.wage = wage;
}
String name;
int age;
float wage;
}
The code is more or less the same from above...but it should give a List of PeopleInfo as output.
List<PersonInfo> peopleInfo = new ArrayList<String>();
boolean isTitleParsed = false;
while ( (line = inputBuffer.readLine()) != null ) {
if (!isTitleParsed) {
// this is the title
title = line;
isTitleParsed = true;
continue;
} else if (line.isEmpty()) {
// this is a blank line; logic for dealing with blank lines here
} else {
String[] personData = line.split("#");
if (personData != null && personData.length == 3) {
peopleInfo.add(new PersonInfo(personData[0],personData[1],personData[2]));
}
}