So I tracked down the bugger, but I am no closer to understanding what is wrong. Here is what the compiler says:
Exception in thread "main" java.lang.NullPointerException at
BasicFile.Search(BasicFile.java:215) at
TestFile.main(TestFile.java:42)
Line 215 is the one that starts with while, first one.
String Search(String key) throws IOException {
int lines = 0;
String line = "";
String foundAt = "";
BufferedReader BF = new BufferedReader(new FileReader(f));
try {
while ((line = BF.readLine().toLowerCase()) != null) {
lines++;
//create tokenizer words with what is in line
StringTokenizer words = new StringTokenizer(line);
while(words.hasMoreTokens()) { //while words has tokens left
//go to next token and compare to key
if (words.nextToken().equals(key.toLowerCase()))
foundAt = foundAt + "\n" + lines + ":" + line;
//do nothing continue loop
}
}
BF.close();
} catch(FileNotFoundException e) {
}
return foundAt;
}
When your buffer reader runs out of lines it returns null. You are trying to call toLowerCase method on null which ends up throwing the null pointer exception.
Refactor your code in a way that it doesn't require you to execute toLowerCase before ensuring the line is non-null.
For example:
String next;
while ((next = BF.readLine()) != null) {
String line = next.toLowerCase();
// ...
}
while ((line = BF.readLine().toLowerCase()) != null)
What happens if BF.readline() returns null?
remove .toLowerCase() from the test
Please, stop it, your code is giving me cancer! There are a number of stylistic errors in the code that you need to fix.
First off in java, method names always begin with a lowercase letter. You are programming in Java, not C#, so you need to use the Java naming conventions. That means your method should be called search, not Search.
The same goes for variable names. What is BF supposed to mean, anyway? Replace it with in, please.
Next up, unless this method is in an object that itself represents that particular file, the global variable f should be passed as a parameter instead.
BufferedReader is AutoCloseable, so you should use a try-with-resources to deal with closing it.
You need to add a javadoc comment to it, documenting its parameters with #param, its return with #return, and exactly why it might need to throw an IOException with #exception.
Here is a mostly-fixed version of your code:
/**
* Needs Javadoc
*/
String search(String key, File f) throws IOException {
int lines = 0
String line = "";
String foundAt = "";
try(BufferedReader in = new BufferedReader(new FileReader(f)) {
while ((line = in.readLine().toLowerCase()) != null) { //the line in question
lines++;
StringTokenizer words = new StringTokenizer(line);
while(words.hasMoreTokens())
if (words.nextToken().equals(key.toLowerCase()))
foundAt = foundAt + "\n" + lines + ":" + line;
}
} catch(FileNotFoundException e){}
return foundAt;
}
Now, the problem here is that in.readline() returns a null sometimes. Calling a method on a null is always a NullPointerException. Therefore you get a NullPointerException when you attempt to call that null's missing toLowerCase() method.
You need to convert it toLowerCase after you ensure it is non-null.
Related
I am working on a game, and I want to use this text file of mythological names to procedurally generate galaxy solar-system names.
When I read the text file, I tell the while-loop I'm using to continue if there is something that's not a name on a given line. That seems to throw an exception in some (not all) areas where there are multiple lines without names.
How can I make the program work without throwing exceptions or reading lines without names on them?
My Code:
public class Rewrite {
public static void main(String[] args) {
loadFromFile();
}
private static void loadFromFile() {
String[] names = new String[1000];
try {
FileReader fr = new FileReader("src/res/names/Galaxy_System_Names.txt");
BufferedReader br = new BufferedReader(fr);
String aLine;
int countIndex = 0;
while ((aLine = br.readLine()) != null) {
// skip lines without names
if (aLine.equals(String.valueOf(System.lineSeparator()))) {
aLine = br.readLine();
continue;
} else if (aLine.equals("&")) {
aLine = br.readLine();
continue;
} else if (aLine.startsWith("(")) {
aLine = br.readLine();
continue;
}
System.out.println(aLine);
// capitalize first letter of the line
String firstLetter = String.valueOf(aLine.charAt(0));
aLine = firstLetter + aLine.substring(1);
names[countIndex++] = aLine;
}
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
The Exception Thrown:
Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 0
at java.base/java.lang.StringLatin1.charAt(StringLatin1.java:47)
at java.base/java.lang.String.charAt(String.java:702)
at utilities.Rewrite.loadHumanNamesFromFile(Rewrite.java:39)
at utilities.Rewrite.main(Rewrite.java:10)
Text-File sample: This throws an error after the name "amor"
áed
áedán
aegle
aella
aeneas
aeolus
aeron
(2)
&
aeson
agamemnon
agaue
aglaea
aglaia
agni
(1)
agrona
ahriman
ahti
ahura
mazda
aias
aigle
ailill
aineias
aino
aiolos
ajax
akantha
alberic
alberich
alcides
alcippe
alcmene
alcyone
alecto
alekto
alexander
alexandra
alexandros
alf
(1)
alfr
alkeides
alkippe
alkmene
alkyone
althea
alvis
alvíss
amalthea
amaterasu
amen
ameretat
amirani
ammon
amon
amon-ra
amor
&
amordad
amulius
amun
From the docs of the BufferedReader::readLine:
Returns: A String containing the contents of the line, not including any line-termination characters
Thus when you get to this part of the file:
amor
&
It will read the blank line and strip the linebreak character, and all that will be left is an empty String. Therefore it will not be caught by your if statement:
if (aLine.equals(String.valueOf(System.lineSeparator())))
You need to add in a check for isEmpty()
After amor is an empty line. You're trying to get the char at index 0 of an empty line. Since it's an empty line, it obviously has no chars, and as such there's no char at index 0
I am trying to iterate through a CSV file in Java. It iterates through the entire file, but will get to the end of the file and try to read the next blank line and throw an error. My code is below.
public class Loop() {
public static void main(String[] args) {
BufferedReader br = null;
String line = "";
try {
HashMap<Integer, Integer> changeData = new HashMap<Integer, Integer>();
br = new BufferedReader(new FileReader("C:\\xxxxx\\xxxxx\\xxxxx\\the_file.csv"));
String headerLine = br.readLine();
while ((line = br.readLine()) != null) {
String[] data = line.split(",");
/*Below is my latest attempt at fixing this,*/
/*but I've tried other things too.*/
if (data[0].equals("")) { break; }
System.out.println(data[0] + " - " + data[6]);
int changeId = Integer.parseInt(data[0]);
int changeCv = Integer.parseInt(data[6]);
changeData.put(changeId, changeCv);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
Like I typed, this works fine until it gets to the end of the file. When it gets to the end of the file, I get the error Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at com.ucg.layout.ShelfTableUpdates.main(ShelfTableUpdates.java:23). I've stepped through the code by debugging it in Spring Tool Suite. The error comes up whenever I try to reference data[0] or data[6]; likely because there is nothing in that line. Which leads me back to my original question of why it is even trying to read the line in the first place.
It was my understanding that while ((line = br.readLine()) != null) would detect the end of the file, but it doesn't seem to be. I've tried re-opening the file and deleting all of the blank rows, but that did not work.
Any idea how I can detect the end of the file so I don't get an error in this code?
ANSWER:
Credit goes to user #quemeraisc. I also was able to replace the commas with blanks, and if the line then equals null or "", then you know that it is the end of the file; in my case, there are no blank rows before the end of the file. This still does not solve the problem of detecting the end of the file in that if I did have blank rows in between my data that were not the EOF then this would detect those.
Solution 1:
if (data.length < 7) {
System.out.println(data.length);
break;
}
Solution 1:
if (line.replace(",", "").equals(null) || line.replace(",", "").equals("")) {
System.out.println(line.replace(",", ""));
break;
}
Just skip all blank lines:
while ((line = br.readLine()) != null) {
if( line.trim().isEmpty() ) {
continue;
}
....
....
The last line may contain some control characters (like new line, carriage return, EOF and others unvisible chars), in this case a simple String#trim() doesn't remove them, see this answer to know how to remove them: How can i remove all control characters from a java string?
public String readLine() will read a line from your file, even empty lines. Thus, when you split your line, as in String[] data = line.split(","); you get an array of size 1.
Why not try :
if (data.length >= 7)
{
System.out.println(data[0] + " - " + data[6]);
int changeId = Integer.parseInt(data[0]);
int changeCv = Integer.parseInt(data[6]);
changeData.put(changeId, changeCv);
}
which will make sure there are at least 7 elements in your array before proceeding.
To skip blank lines you could try:
while ((line = reader.readLine()) != null) {
if(line.length() > 0) {
String[] data = line.split(",");
/*Below is my latest attempt at fixing this,*/
/*but I've tried other things too.*/
if (data[0] == null || data[0].equals("")) { break; }
System.out.println(data[0] + " - " + data[6]);
int changeId = Integer.parseInt(data[0]);
int changeCv = Integer.parseInt(data[6]);
changeData.put(changeId, changeCv);
}
}
Instead of replace method use replaceAll method. Then it will work.
This is a quick one that stumps me. I've got a Java Program with the following code:
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
String file1 = args[0];
String file2 = args[1];
String output = args[2];
Writer writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(output), "utf-8"));
// Get the file
BufferedReader br1 = new BufferedReader(new FileReader(file1));
ArrayList<String> masterRBT = new ArrayList<String>();
// Read the files
while(br1.readLine() != null) {
masterRBT.add(br1.toString());
System.out.println(br1.toString());
}
Read the file (in this case, a .csv), and output it to the command line.
I use the command line to run the program, plus three parameters, using so (it only really uses the first one):
java -jar csvdiff.jar mainfile.csv subfile.csv output.csv
But then, it returns this:
java.io.BufferedReader#17dfafd1
Repeatedly, as if on loop. I tried putting in a Try/Catch error, but it still does the same - no errors. I've opened the .csv files, and verified its contents.
The CSV files are located in the same directory as the .jar file.
What am I missing?
because you are attempting to print an instance of BufferedReader not the data you are reading from it
Change
while(br1.readLine() != null) {
masterRBT.add(br1.toString());
System.out.println(br1.toString());
}
to
while((String line = br1.readLine()) != null) {
masterRBT.add(line);
System.out.println(line);
}
You're printing out br1.toString() - you're calling toString() on the BufferedReader itself. BufferedReader doesn't override toString(), so you're getting the implementation from Object, as documented:
The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character #, and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:
getClass().getName() + '#' + Integer.toHexString(hashCode())
That's not what you want. Presumably you actually want to print out the line that you've just read - but you've thrown that away by now. You want:
String line;
while((line = br1.readLine()) != null) {
masterRBT.add(line);
System.out.println(line);
}
Or as a for loop:
for (String line = br1.readLine(); line != null; line = br1.readLine()) {
masterRBT.add(line);
System.out.println(line);
}
As a general matter, if you start seeing ClassName#Number in output, that's almost certainly a similar problem of calling toString() on an object which doesn't override it.
You are not printing the line but the reader itself, to print the line change your code like this:
// Read the files
String line;
while((line = br1.readLine()) != null) {
masterRBT.add(line);
System.out.println(line);
}
Use this,
String str;
while((str=br1.readLine()) != null) {
masterRBT.add(str);
System.out.println(str);
}
Because BufferedReader.toString() just returns the class name and hash value of the object.
Use BufferedReader.readLine() to get the String instead.
The code below is mostly self explanatory. However, I am having trouble in two cases:
The while loop does not exit even with the command line is left blank.
If the input is test t1 the key variable is supposed to be "test" (using System.out.println(key)) does that, but, it still doesn't enter the if condition for some reason.
String[] broken_text = null; String text = "";
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
while((text = reader.readLine()) != null) {
broken_text = text.split(" ");
String first_key = broken_text[0];
if (first_key == "test") {
//some statements
}
}
I am not sure why this is happening, any help regarding the same will be much appreciated.
use equals() to check string equality.
if (first_key == "test") {
//some statements
}
should be
if (first_key.equals("test")) {
//some statements
}
your text will never be null because you declared it as
String text = "";
thus your while loop would be an infinite loop
change
String text = "";
to
String text = null;
or if you wanna leave your text="" string as empty string.
use
while(!(text = reader.readLine()).isEmpty())
The loop does not end because a blank line causes readLine() to return an empty string, not null.
The comparison fails because Strings must be compared with equals() not ==
The String text will never be null in this case. You can use:
while (!(text = reader.readLine()).isEmpty()) {
this should be your edited code:
String[] broken_text = null;
String text = "";
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
while((text = reader.readLine()) != null && !text.isEmpty()) {
broken_text = text.split(" ");
String first_key = broken_text[0];
if ( "test".equals(first_key)) {
//some statements
}
}
The reason changed (text = reader.readLine()) != null to (text = reader.readLine()) != null && !text.isEmpty() is because readLine() returns null when it encounters end-of-file as the first character, and it returns "" (empty string) when the first character is encounters is \r (carriage return), \n(line feed) , or \r\n(carriage return followed by line feed). And you must always check for null before checking for isEmpty().
On unix / Linux console end-of-file is [ctrl][d] and on DOS it is [ctrl][z]
Note: In case you want to read input from a file (where you are more likely to get an end-of-file) instead of console, then your reader will be initialised like this:
BufferedReader reader = new BufferedReader(new FileReader("d:\\a1.txt"));
(assuming your input data is in file: "d:\a1.txt".)
I'm trying import CSV file to Arraylist using StringTokenizer:
public class Test
{
public static void main(String [] args)
{
List<ImportedXls> datalist = new ArrayList<ImportedXls>();
try
{
FileReader fr = new FileReader("c:\\temp.csv");
BufferedReader br = new BufferedReader(fr);
String stringRead = br.readLine();
while( stringRead != null )
{
StringTokenizer st = new StringTokenizer(stringRead, ",");
String docNumber = st.nextToken( );
String note = st.nextToken( ); /** PROBLEM */
String index = st.nextToken( ); /** PROBLEM */
ImportedXls temp = new ImportedXls(docNumber, note, index);
datalist.add(temp);
// read the next line
stringRead = br.readLine();
}
br.close( );
}
catch(IOException ioe){...}
for (ImportedXls item : datalist) {
System.out.println(item.getDocNumber());
}
}
}
I don't understand how the nextToken works, because if I keep the initialize three variables (docNumber, note and index) as nextToken(), it fails on:
Exception in thread "main" java.util.NoSuchElementException
at java.util.StringTokenizer.nextToken(Unknown Source)
at _test.Test.main(Test.java:32)
If I keep docNumber only, it works. Could you help me?
It seems that some of the rows of your input file have less then 3 comma separated fields.You should always check if tokenizer has more tokens (StringTokenizer.hasMoreTokens), unless you are are 100% sure your input is correct.
CORRECT parsing of CSV files is not so trivial task. Why not to use a library that can do it very well - http://opencsv.sourceforge.net/ ?
Seems like your code is getting to a line that the Tokenizer is only breaking up into 1 part instead of 3. Is it possible to have lines with missing data? If so, you need to handle this.
Most probably your input file doesn't contain another element delimited by , in at least one line. Please show us your input - if possible the line that fails.
However, you don't need to use StringTokenizer. Using String#split() might be easier:
...
while( stringRead != null )
{
String[] elements = stringRead.split(",");
if(elements.length < 3) {
throw new RuntimeException("line too short"); //handle missing entries
}
String docNumber = elements[0];
String note = elements[1];
String index = elements[2];
ImportedXls temp = new ImportedXls(docNumber, note, index);
datalist.add(temp);
// read the next line
stringRead = br.readLine();
}
...
You should be able to check your tokens using the hasMoreTokens() method. If this returns false, then it's possible that the line you've read does not contain anything (i.e., an empty string).
It would be better though to use the String.split() method--if I'm not mistaken, there were plans to deprecate the StringTokenizer class.