Using Serializable To Write Everything To A File At Once?
Nov 3, 2014
For a class, I'm making a prison system program. The prison has cell blocks, each cell block has cells, each cell has bed(s), and each bed has prisoners. There are also visitors and visits. I thought, rather than write all of those to different files, I could just write the entire prison to a file and make all the classes under it implement serializable. The instructor said that is a bad practice and we shouldn't do it. So I'm thinking I'll make the prison non-serializable. But the prison has maps of cell blocks, inmates, visitors, and visits. I think I'll make all those serializable and I'll also make everything a cell block contains serializable as well. Then I can just read the cellblocks from the file. But is that too easy as well? Is that a bad practice?
I have two JFrames the first one is a log in screen where i log in to the log in server that i made using RMI . If the log in succeeds i send the user object witch is Serializable to the second JFrame.
The user object is received from the server. This object contains all the information needed in the second JFrame. This second JFrame is made inside the first one and i defined a method with witch i send this user object to the second frame.
Now the problem arises , while inside this method i am able to read all the data i need from the user object. At the end of the method i save the reference of this object in a new User object defined in the second JFrame ,because i need it later on.
But soon as this method finishes , for some reason my reference to the object becomes null , and i cant use it later on.
This program is basically complete. It compiles and runs. It is a college course assignment that I pretty much completed but for the last part in which I'm suppose to change the values of all fields and display the modified values using a toString method. Modifying the values of the fields is where I am stuck. I don't think I need to create a new text data file to do this. The instructor only asked that all the values of fields be changed and this was the last part of the assignment so I don't think it involves creating additional ObjectOutputStream and ObjectInputStream objects. I'm getting a NullPointerException error on line 161.Here is the code. I'm also including the input data file.
//create program so that objects of class can be serialized, implements interface Serialiable //create constructor with 4 parameters with accompanying get and set methods, Override toString method //create text file with 5 records, create Scanner object,ObjectOutputStream, and ObjectInputStream //create new ItemRecord object, change values of all fields in ItemRecord object using object's set methods //modify ItemRecord object using toString method
[hightlight =Java]import java.io.Serializable; public class ItemRecord implements Serializable
----jGRASP wedge2: exit code for process is 1. ----jGRASP: operation complete.
Here is the data file: A100 99.99 10 Canon PowerShot-135 A200 149.99 50 Panasonic-Lumix T55 A300 349.99 20 Nikon- D3200 DSRL A400 280.99 30 Sony- DSC-W800 A500 97.99 20 Samsung- WB35F
Here is the data file for the modified field values. B100 98.00 10 ABC1010 B200 97.00 15 DEF1020 B300 96.00 10 GHI1030 B400 95.00 05 JKL1040 B500 94.00 01 MNO1050
is my current exercise.so far i have gotten the code to create a file, and ask the user to input their age.what should i use to save what the user writes into the file?
Java Code:
package assignment7; import java.io.*; import java.util.*; public class Exercise2 { public static void main ( String [ ] args ) throws IOException { Scanner scan = new Scanner(System.in);
I have created a program that allows a pizza shop to enter a customers orders (via 3 seperate panels of options), and calculate a total. Everything works just fine, and now we have to take it a step further and record the sale data in a .txt file (which will include the Crust Type, Toppings, and Extras).
I need to make it so that when a user clicks the calculate button, it also writes to a file (in this case, SalesRecords.txt). I have it all set up, but for some reason I can not get it to work. The error I get is:
"error: unreported exception FileNotFoundException; must be caught or declared to be thrown PrintWriter outputFile = new PrintWriter(filename);
Here's my code: (the calculate button that I am working with is indicated by a comment)
[I looked up the exception I got, and just so everyone knows I made sure that the file "SalesRecords.txt" DOES EXIST. It is in the same folder as my java and class files for this program. I even tried defining the absolute file path for SalesRecords.txt and that changed nothing.
My program successfully reads a file, reports back what it finds and creates an output file. However, I cannot get it to write to the output file, it is always blank!
Here's my code:
import java.util.Scanner; import java.io.*; public class Ex19 { public static void main (String [] args) { //Variables
I want to write a text area to a file which I have accomplished however the formatting for how it is written into the text file is different. Is there a different library I must use to retain the formatting?
I'm using a BufferedWriter to write to the file
if (!file.exists()) { try { BufferedWriter output = new BufferedWriter( new FileWriter(file)); output.write(textArea.getText()); output.close(); } catch (IOExcception io) { io.printStackTrace(); } }
I extended the SimpleFileVisitor class. And I am able to traverse the file directories. I give a file path then have it display the files full path and out put that to a text file. Here is what i have so far.
public class Main { public static void main(String[] args) throws IOException { Path fileDir = Paths.get("somedirpathhere"); FileTraversal visitor = new FileTraversal(); Files.walkFileTree(fileDir, visitor);
[code]...
I am able to printout of the arraylist to the console. I cant get it to write to a text file whats in the arraylist to a text file.
package shoppingcartselection; import javax.swing.*; import java.util.ArrayList; public class Main { public static void main(String[] args) { ArrayList<Item> items = new ArrayList<>();
[Code] .....
I have it to save to a text file the subtotal, sales tax, and the total cost of all items in the cart after clicking on Checkout. I need it to also show the Items that where in the cart, along with how much each Item costs. I've tried this:
public void save(ArrayList Receipt) throws FileNotFoundException { PrintWriter pw = new PrintWriter(new FileOutputStream("Receipt.txt")); for (Item itemsInCartNames : itemsInCart) pw.println(itemsInCartNames); pw.close(); }
But this is what gets saved to the Receipt.txt file:
I want to write byteArray in file from String and if "/n " newline comes in String it should write from next line in file. I tried and no content starts from newline in file.
Suppose String s= "This is my Java Program /n Converting string to byteArray";
Output in file should be as :
This is my Java Program Converting string to byteArray
When i am converting byteArray in String, it showing me same output as i wants but not in file.it showing me on console.
psvm(String arr[]){ String s= "This is my Java Program Coverting string to byteArray"; FileOutputStream fos = new FileOutputStream("filepath"); fos.write(s.getBytes()); fos.close(); }
output in file : This is my Java Program Converting string to byteArray
Any other way to get content after newline in next line.
I'm rather new to programming and I'm trying to make a gui program that will allow the user to create text files. They will be prompted to enter what they'd like to save their file as and then they will be allowed to input text to that file . They will also be allowed to open their files to modify or view its contents. So to start things off, I'm making a prototype if you will.. I've been able to save to a file the problem occurs when I try to read/display it.
Main Class:
public class MainActivity { public static void main(String[] args) { // Access to other classes WriteFile writer = new WriteFile(); ReadFile reader = new ReadFile();
My background is mainframe and i'm new to java. We're moving from mainframe to the java world and I'm trying to achieve a task. I have a main folder and then bunch of sub folders and each sub folder has bunch of xml files, files size are varies some of them are 900kb. I need to read these xml files and send the output to the txt file (comma separated).
Some possible options or sample example... Please find below the sample xml file. I need to extract information's only where
I wanna learn to create a method where I use a scanner or any other way to input.The stuffs I input will be strings. The whole thing will be like a destination creator.So if I input the string USA, it will write this to a file:
1:USA
When I go to the method again the ID will be added so if I input UK, the file will contain:
1:USA 2:UK
Now if I terminate the program, next time when I run it again it will be able to read the ArrayList, so if I wanna go to the method again and write: Norway the file will contain:
1:USA 2:UK 3:Norway
Later I also want to be able to use println to show all of these lines from the file, as well I would like to be able to delete an ID, so if I delete ID 2 the file would contain:
1:USA 3:Norway
I'm quite new to Java, I'm in a Java course since soon 3 weeks back and I have sure learned a lot, all the loops and basic statements that exist in most languages, but now when it comes to this I just don't understand.
I got a question in my last interview, its all about multithreading, interviewer asked me to write a program, to write the contents of three files(F1,F2,F3) in to a new File F4, using multithreading , first thread should read the first file and second thread should read second file, so the File F4 should contain F1's contents in first then F2's contents after that etc. I tried to give my best shot, but i couldn't get a way to ensure that the first thread is reading the first file and write to F4 then second thread reading the second file and writing once first file is written completely into F4 and so on ..how to do this?
Google shows me how to use file I/O, and how to use stdio, but not how to combine the two easily.
With my *nix command line I could "program file | tee savefile", but savefile holds the result of prior runs, gets read before I parse 'file', and this command line zero's out savefile before the program can read it.
The data is standard ASCII, I doubt I'll ever have 20k of data.
What i basically do is that i read the information of what course that needs to be updated with a new course date and then i log into the wordpress page and navigate to the course and add the date.
I need the java program to be able to do these following actions.
1. Open a webpage
2. write to a form
3. click a button
4. search for a text on screen
5. click on a specific place on the screen/click on a link
So I am calling this method several times and trying to write multiple records to a file. Problem is that every time I call the method it overwrites the file from before and doesn't add it.
public void fileWriterMethod() throws IOException{ RandomAccessFile raf = new RandomAccessFile(filename, "rw"); raf.writeInt(id); raf.writeInt(existingMileage); raf.writeInt(gasCost); raf.writeInt(ndays); raf.writeInt(rate);
