Can Database Storage And Queries Replace All Collections And Arrays (which Basically Hold Data)
Jan 10, 2014
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....??
would like to make .jar application, which will be able to sava data without using any database (Postgres...) but i dont know, what type of datastorage i should use to make the application portable. I just want to .jar file, which is capable works on any computer with java installed. Is there some option?
I am trying to create a java program to sort an array in ascending and descending order. Here is the program I created :
import java.util.Arrays; import java.util.Collections; public class ArraySort { public static void main(String [] args) { int [] num = {5,9,1,65,7,8,9}; Arrays.sort(num);
[Code]...
BUT I GET THE FOLLOWING EROOR ON COMPILATION
ArraySort.java:12: error: no suitable method found for reverseOrder(int[]) Arrays.sort(num,Collections.reverseOrder(num)); ^ method Collections.<T#1>reverseOrder(Comparator<T#1>) is not applicable
I have a class with static ArrayLists to hold objects such as Members,Players etc.I want to save the class with the arrays so as to reload them again and hold onto the list of objects within those ArrayLists.
The ArrayClass
import java.io.Serializable; import java.util.ArrayList; public class ArrayClass implements Serializable {
[code]....
The arrays within the ArrayClass are empty when i reload the application.I cant tell if the arrays are being properly saved or is it in the reloading from file???
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...
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 .
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 .
I am unable to post my code, it redirects me to a 'Page not found' page.
The problem with my program is a variable that I have initialized, is being said its not being initialized.
I am working on my second javafx program and I am getting confused. The program that I am writing is a payroll calculator. A secondary window opens at the start of the program where the user first enters the number of employees and clicks submit to save the number and to close this window. Then, the user begins to enters the employee information (first name, last name, pay rate and hours worked) when the user clicks the NextEmp button, I want the data in the text fields to be entered into arrays for later use, then clear the fields for the next use. I am running into 2 issues. The first is the close event for the secondary window that pops up. I cannot figure out the syntax. The second issue that I am running into is the loop to store the data into the arrays. I believe I am getting the text field data correctly, but I cannot figure out how to stop the loop until the NextEmp button is pressed again.
I am just learning arrays or rather teaching myself about them and I am not to sure how they work and why. I understand that in order to set one up you do
int[] example1; example1 = new int[]{01, 02, 03, 04};
But I don't really understand is why if you only need 3 data integers, why put the 4th one in?
Also with outputting data, I understand .print() and .println() but I am not to sure what .printf() does and then the formatting after that.
System.out.printf("%3d%11") // and then what you want to print
The international Olympics Committee has asked you to write a program to process the data and determine the medal winners for the pairs figure skating. You will be given the following file: Pairs.txt
Which contains the data for each pair of skaters. The data consists of each skater's name, their country and the score from each of eight judges on the technical aspects and on the performance aspects. A typical record would be as follows:
Smith Jones Australia 5.0 4.9 5.1 5.2 5.0 5.1 5.2 4.8 4.3 4.7 4.8 4.9 4.6 4.8 4.9 4.5
The final score for each skater is the sum of the average of the two categories of score. Design a class to hold the above data and the final score. Read the data in from the file and calculate the final score for each pair. Sort the array of objects , and display the results on the screen in order, giving special prominence to the medal winners.
Here is my CLass:
public class Skaters { private String name1; private String name2; private String country; private double [] arrTech = new double [8]; private double [] arrArt = new double [8]; private double score;
[code]...
how do i print my 2 arrays using the file? i got the name1, name2 and counntry to print but im stuck on printing the scores that are stored in the arrays. Also, i have to print the average for each array. one is for techniques and the other one is artistic. as you can see i already wrote the code for it but im stuck in printing it.
I am having some trouble with a Java program. I have a txt data file, which I will display, that I need to add into two separate arrays. The text file is 8 lines long that is supposed to go into two separate 4x4 matrices. A little background info on this program, reads in two arrays, compares them and outputs the largest elements of the same index and outputs them in a separate array. I somehow cannot seem to figure out how to do this. My code is below:
I am still working on my java course and now we have to create a jar file from a previous project (this is a project where a connection to the database is made and data is shown in a frame).
When I follow the instruction in my course material I don't get it to work. I've tried the following:
1. Open eclipse on windows xp 2. Right click on the project folder in eclipse 3. Click on "export" in the menu that appears 4. Choose "runnable jar" 5. click next 6. I insert the following parameters:
- Launch configuration --> I select my main class - export destination --> I select the folder D: - library handling --> Package required libraries into generated jar
7. click Finish
This is what happens when I dbl click the jarfile (wampserver is running):
1. I get an error: "SQL ERROR: Communications link failure The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server."
2. I click ok on the message and the following message appears: "SQL Error: null"
3. I click ok on this message and the frame with the fields appears without data from the database.
I can insert data to table by using JSP Scriptlet easily but I have a hard time with servlet.
public class UsertToDatabase() { public boolean inserUser(String name, String email, String pwd) throws SQLException { PreparedStatement pstmt = null; boolean flag = false; System.out.println("start"); openConn(); System.out.println("start_1"); if(conn == null) {
[code]....
I am positive that the above code function fine. The problem is whenever I call UserToDB() class inside the servlet, and I got this error: java.lang.ClassNotFoundException: org.postgresql.
Driver which mean that my conn (connection) is not connected to the database but I have ensure to do so by calling openConn() before start the transaction.
try { is = new FileInputStream(file); data = new byte[(int) file.length()]; is.read(data); String extension = ""; int i = file.getName().lastIndexOf('.'); if(i>0)
[Code] ....
Everything works except transferring the image file.
I need my java program to insert data into my access database. I get no errors in my code, but it never inserts, deletes the data in my database. Here is my code:
import java.awt.*; import java.awt.event.*; import java.sql.*; public class INS extends Frame implements ActionListener{ Frame f; Label l1, l2; TextField t1, t2; Button b1, b2, b3, b4, b5; Connection c;
I have tried this code to insert into datbase if not exists but i get an Exception in thread "main" com.mysql.jdbc. exceptions.jdbc4. MySQL SyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHERE NOT EXISTS (SELECT teamName FROM Teams WHERE teamName = teamName) LIMIT 1' at line 1
stmt.executeUpdate("INSERT INTO Teams(teamId,teamName,league) VALUES ("+i+",'"+loser+"','"+league2+"')WHERE NOT EXISTS (SELECT teamId,teamName,league FROM Teams WHERE teamName = teamName) LIMIT 1;");
I need getting detailed examples about how I can read/insert into database using JSF code for its different components. I am a beginner in JSF and I have the basics, however, I need the best source which it has useful, easy and detailed steps to understand the techniques for connecting to the DB and how to insert or read data from the database.
I tried to search, but I found the lessons are not useful or not described in details.
I have a simple project to save data to the database. I have successfully mapped the java class with the database table. The code displays no error, it runs very well but it does not save to database, instead it catches an exception and prints out "saving failed". The database is a mysql database.
This is the managed bean code. Save.java(name=bean)
//imports
@ManagedBean(name="bean") @RequestScoped public class Save { private String username,password,msg; Session session = null; Transaction transaction = null; //GETTERS AND SETTERS public Save() {
[Code] ....
This is a screenshot of my Hibernate configuration file : hb.jpg
