Importing CSV / Reading Data And Have A Count Using Queries
Oct 11, 2014
Ok so I know how to import a csv using java. What I'm curious about doing is importing a csv using file chooser, reading the data, sorting the data out by certain parameters, and then outputting a count of each parameter I chose. Say for example I have columns 1,2 and 3. Column 1 has the name, column 2 has the percentage, column 3 has an o'clock time. I want to use queries to sort through the parameters and have a count of each parameter I choose...
My friends and me are trying to make online Test taking system. We got a very basic doubt.
We have developed classes and relationship between classes for example : Online Test Taking system will have admin and student class. And Admin will have list of students.. etc.
But question troubled me was: if we use database to store all data for example student details then I can perform all sorts of operations writing sql query and store result in some other database then what is the need of "ArrayList<Student> field in Admin".??
Question is: We can put everything in database and manipulate using database(sql) functions to manipulate it.Then what is the need of Arraylist of anything which is just used to store object details for example student details....??
I am creating a program where it reads the data inside a file and then places this data into arrays. The file I created has numbers 1-30 in it, file named, testing1.txt .
Let's say hypothetically you're making a huge program and use a lot of imports (ex import java.util). If you only need a few specific things from java.util, will it use more memory importing java.util.* compared to only importing lets say java.util.Scanner, java.util.ArrayList, etc. Basically does importing a whole package use more (if any at all) memory than only importing specific package parts?
I have two programs that talk to each other over a TCP connection. When I write the data "STX+1234" where STX is the Ascii character STX or Ctrl B and I expect the written String length to be 6 which it is. On the other side of the socket I create the ServerSocket and use the client socket's InputStream to create a BufferedReader. When I receive the string it now has 12 characters where each original character has been replaced by NUL and the character. How do I read the string as it is originally specified without the conversion? And is the problem on the reader side or the writer side?
I can read the data to a monitor perfectly. But, I'm having problem reading data from an external file into an array of class objects. Here's my attempt at writing the method:
private void openFile() //This method asks the user to enter a file name(including the file extension) and then //Sets the data to an array of Product type { String fileName, storeName="", emptyLine1="", emptyLine2="", name="", productName=""; int demandRate=0; double setupCost=0.0, unitCost=0.0, inventoryCost=0, sellingPrice=0; Scanner inputStream = null;
A method in Java returns a schema. In .net, we use DataTable to get the data from the schema. How to write the following code in Java:
/* Result r = method(); r.DataSchema; */ using (DataTable tbl = new DataTable()) { using (MemoryStream ms = new MemoryStream()) using (StreamWriter sr = new StreamWriter(ms))
I am reading Excel data using java apache. I got format issue while reading double value such as 869.87929 (in excel) into 869.8792899999999 (in java).
if(type.equals("Double")){ String str = content[i-1]; //System.out.println(str); BigDecimal d = new BigDecimal(str); listObjects.add(d); }
Note: type from schema.csv & content [] value from file.xls If I print **str**, it shows value as 869.8792899999999. But i need to get **str** value as 869.87929. How can I get it?
I have an array with the following characters {'E', 'L','E','P','H','A','N','T','P','O'}
now, I need an array that will store the first array such that only the occurence occurs e.g {'E','L','P','H','A','N','T','O'} Notice that the characters 'E' and 'P' occur twice and as a result were not repeated the second time in the new array.
How would one go about this using the counting elements technique?
I tried this but not sure how to use the counting elements technique.
char [] arr = new char{'E', 'L','E','P','H','A','N','T','P','O'}; char[] bucket = new char[(arr[0] * arr.length)]; for (int i = 0; i < len; i++) bucket[arr[i]]++;
I have to read data from a text file and print it in a new text file. An example of one line is like this: Johnson 85 98 75 89 82
I then have to take the average of all the numbers and assign a "grade" to the numbers for each line of the text file and make a new file so it looks like this for 10 lines:
Name 1 2 3 4 5 Average Grade
Johnson 85 98 75 89 82 85.80 B
My problem is extracting the data from the file so I can use it.
The problem is that I often receive ArrayOutOfBound errors when I try to parse the byte array. I think that I'm reading from the socket in a wrong way..
I'm a complete beginner in Java programming and I'm interested to learn more about its concepts.
Recently, I've been given an exercise which instructs me to display two versions of a picture. The picture to be displayed is provided in the form of a data file of 40,000 digits that are arranged in rows (although there is no marker between rows) and it starts from the top of the picture. So the first digit represents the top left corner of the picture and the last is the bottom right.
Basically, what the exercise wants me to construct a program that plots a dot in one of two colours for each digit. If the digit is in the range 0 to 3 the output should be one colour and for digits in the range 4 to 9 the dot should be in the other colour.
I understand I have to use arrays and also loops to perform this. I'm familiar with the fillEllipse, drawEllipse, drawRectangle and fillRectangle but this exercise is nothing I've attempted before.
We have an autosys job running in our production on daily basis. It calls a shell script which in turn calls a java servlet. This servlet reads these files and inserts the data into two different tables and then does some processing. Java version is 1.6 & application server is WAS7 and database is oracel-11g.
We get several issues with this process like it takes time, goes out of memory etc etc. Below are the details of the way we have coded this process.
1. When we read the file using BufferedReader, do we really get a lot of strings created in the memory as returned by readLine() method of BufferedReader? These files contain 4-5Lacs of line. All the records are separated by newline character. Is there a better way to read files in java to achieve efficiency? I couldnt find any provided the fact that all the record lines in the file are of variable length.
2. When we insert the data then we are doing a batch process with statement/prepared statement. We are making one batch containing all the records of the file. Does it really matter to break the batch size to have better performance?
3. If the tables has no indexes defined nor any other constraints and all the columns are VARCHAR type, then which operation will be faster:- inserting a new row or updating an existing row based upon some matching condition?
I'm having a bit of trouble with using the Scanner and the Printwriter. I start with a file like this (1 = amount of Houses in the file)
1 FOR SALE: Emmalaan 23 3051JC Rotterdam 7 rooms buyprice 300000 energylevel C
The user gets (let's say for simplicity) 3 options:
1. Add a House to the file, 2. Get all Houses which fullfil requirements (price, FOR SALE / SOLD etc.) and 3. Close the application.
This is how I start:
Scanner sc = new Scanner (System.in); while (!endLoop) { System.out.println("Make a choice); System.out.println("1) Add House"); System.out.println("2) Show Houses"); System.out.println("3) Exit"); int choice = sc.nextInt();
Then I have a switch for all of the three cases. I keep the scanner open, so Java can get the user input (house = for sale or sold, price = ... etc). If the user chose option 1, and all information needed is inputted and scanned, the House will be written to the file (which looks like what I typed above).
For this, I use try (PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("Makelaar.txt", false)))). This works perfectly (at least so it seems.)
If the user chose option 1, and all requirements are inputted and scanned, the Houses will be read (scanner) from the file and outputted. For this I use the same Scanner sc. This also works perfectly (so it seems atleast).
My problem is as follows: If a House has been added, I can only read the House(s) which were already in the file. Let's say I have added 2 houses, and there were from the start 3 houses. If option 2 is chosen, the first 3 houses will be scanned perfectly. An exception will be caught for the remaining 2 (just added) Houses. How can I solve this? I tried to close the Scanner, and reopening it, but apparently Java doesn't agree with this
How can I Cache the data I'm reading from a collection of text files in a directory using a TreeMap? Currently my program reads the data from several text files in a directory and the saves that information in a text file called output.txt. I would like to cache this data in order to use it later. How can I do this using the TreeMap Class? These are the keys,values: TreeMap The data I'd like to Cache is (date from the file, time of the file, current time).
import java.io.*; public class CacheData { public static void main(String[] args) throws IOException { String target_dir = "C:Files"; String output = "C:Filesoutput.txt"; File dir = new File(target_dir); File[] files = dir.listFiles();
Lately I've been working with JDBC and writing queries in some Java programs. I've noticed that I keep experimenting with where I place my blocks of querying code. I've tried creating a private method in the class where the query is used, I've created utility classes where I can call the query when needed, and sometimes I've just put it in a localized block of code where I need to. Also, most often these queries are one-shot queries where I need to pull the data to populate a JTable.
In short, this has made me realize that I don't have a solid practice for organizing my queries in Java. So my question is "Is there a practice for organizing query code?".
I am new to JSTL and JSP & I am running 2 seperate SQL queries from a java/jsp program and I need to display the results from both queries on one JSP page output.Currently I have java code that passes the 2 queries to a method along with passing the jsp files to output the query results
- the method dispatches the results to these 2 JSP pages using JSTL tags in hope for separate output results:
I need to have a way to display these 2 outputs into 1 jsp page: - currently one just overwrites the other.I also tried using the jstl core <c: tags in 2 separate methods on the same jsp page but the <c: tags just resulted in overwriting one another - The queries run and display fine except I cannot get them both to display correctly.using jstl and jsp for displaying multiple queries on the same page.example: the jsp file that runs the queries:
I have a question about query execution strategy ...
Scenario: let's suppose I've to query a table with a query like
SELECT F1, F2, F3 FROM MYTABLE WHERE F1 = ? AND F2 = ? AND F3 = ?.
I need to execute this query changing parameters' actual values in a combinatorial way, until a combination gives back at least one row or all combinations are unsuccessfully tried. For instance, I may have this sequence of values:
(V1,V2,V3); (V1,V2,""); (V1,"",V3); (V1,"","");
where V1, V2, V3 may by string values and V1 is always present, not null, and not blank in each combination.
A first strategy may be to prepare the statement, clear the parameters each time I execute the query, until stop condition is met.
I wonder if may be more efficient transform the query into
SELECT F1, F2, F3 FROM MYTABLE WHERE F1 = V1
and cycling over the cursor and, for each cursor row, verify if the returned tuple (F1,F2,F3) matches the combination (V1x,V2x,V3x). When at least 1 rows matches, or all combination are done, I'll exit iteration.
javax.xml.parsers.DocumentBuilder can build a document from a single stream which is the XML file. However, I can't find any way to also give it a schema file.
Is there a way to do this so that my XPath queries can perform type aware queries and return typed data?
We presently use dom4j/jaxen and it does this fine but I figure we should switch to the standard Java runtime if this has been added.
I have one problem regarding Running Multiple queries parallely and storing results in resultsets . I have multiple queries but I need to executing all at a time without having to wait for one query to complete execution and then run another as there are 2 queries say query1 takes 10 mins and hence query2 should also start simultaneously and not wait for query 1 for completion.
String query1="select * from knowledge_rep"; String query2="select * from events"; ResultSet rs=null; PreparedStatement ps =con.prepareStatement(query1); rs=ps.executeQuery(); ps =con.prepareStatement(query2); rs1=ps.executeQuery();
[Code] ....
The above one is time consuming and second implementation using branch i wont be able to resolve it to result set using execute batch. Considering there are multiple select queries and the number of queries to be executed are dynamic and unknown and all the data from the queries are needed. Any leads to perform all these by running multiple threads simantaneously.
