Develop Reference

Using parsed input from text file as parameter for new Event

I've working on an assignment that asks me to alter a method in a class to take content from a textfile and use it to create multiple instances of various subclasses of the Event Class. Here is the text file:
Event=ThermostatNight,time=0
Event=LightOn,time=2000
Event=WaterOff,time=8000
Event=ThermostatDay,time=10000
Event=Bell,time=9000
Event=WaterOn,time=6000
Event=LightOff,time=4000
Event=Terminate,time=12000
The Event=* is the name of the subclass, while time=* is a parameter that is used in the subclass' constructor. The Event class itself is an abstract class and is used for inheritance.
public class Restart extends Event {
Class eventClass;
String eventInput;
Long timeDelay;
public Restart(long delayTime, String filename) {
super(delayTime);
eventsFile = filename;
}
public void action() {
List<String> examples = Arrays.asList("examples1.txt", "examples2.txt", "examples3.txt", "examples4.txt");
for (String example : examples) {
//finding pattern using Regex
Pattern pattern = Pattern.compile(example);
Matcher matcher1 = pattern.matcher(eventsFile);
if (matcher1.find()) {
File file = new File(example);
String line;
try {
FileReader fileReader = new FileReader(file);
Scanner sc = new Scanner(file);
BufferedReader bufferedReader =
new BufferedReader(fileReader);
while ((line = bufferedReader.readLine()) != null) {
sc.useDelimiter("\n");
//Parsing through text
while (sc.hasNext()) {
String s = sc.next();
String[] array1 = s.split(",");
String[] array2 = array1[0].split("=");
eventInput = array2[1];
String[] array3 = array1[1].split("=");
String timeInput = array3[1];
try {
eventClass = Class.forName(eventInput);
timeDelay = Long.parseLong(timeInput);
try {
addEvent(new eventClass(timeDelay));
}
//catch block
catch(NoSuchMethodException e){
System.out.println("No Such Method Error");
} catch (Exception e) {
System.out.println("error");
}
//catch block
} catch (ClassNotFoundException ex) {
System.out.println("Unable to locate Class");
} catch (IllegalAccessException ex) {
System.out.println("Illegal Acces Exception");
} catch (InstantiationException ex) {
System.out.println("Instantiation Exception");
}
}
}
//Close bufferedReader
bufferedReader.close();
}
//catch block
catch (FileNotFoundException ex) {
System.out.println(
"Unable to open file '" +
file + "'");
} catch (IOException ex) {
ex.printStackTrace();
}
break;
}
//if input match is not found
else {
System.out.println("No Match Found");}
}
}
I seem to be able to parse fine, and find the strings i'm looking for, but I'm not able to use eventInput which I've pulled from the text file as a parameter to create a new event.
eventClass = Class.forName(eventInput);
doesn't seem to be turning my string into an acceptable parameter either.
Any help would be much appreciated!
I know I'm probably missing something key here, but I've been staring at it too long that it seems like a lost cause.
Here is the Event class:
public abstract class Event {
private long eventTime;
protected final long delayTime;
public Event(long delayTime) {
this.delayTime = delayTime;
start();
}
public void start() { // Allows restarting
eventTime = System.currentTimeMillis() + delayTime;
}
public boolean ready() {
return System.currentTimeMillis() >= eventTime;
}
public abstract void action();
} ///:~

I think you've misunderstood how reflection works. Once you have a Class object (the output from Class.forName(), you have to find the appropriate constructor with
Constructor<T> constructor = eventClass.getConstructor(parameter types)
and then create a new instance with
constructor.newInstance(parameters);
For a no-arg constructor there's a shortcut
eventClass.newInstance();
I strongly suggest you read the tutorials on reflection before proceeding.

Java read file with scanner

I have this code that have some methods for creating a file, adding data to the file and then read the file with scanner.
My problem is that I want it to run my three methods at once but it stops
at the method number two and does not read the file with readFile() method
createFile();
addResponses(file);
readFile(file);
I can not run these three together. It does not read the file. But if I take
the other methods away like this
//createFile();
//addResponses(file);
readFile(file);
Then the read file method works.
I hope you did understand my problem. Is there something wrong with my code?
import java.io.*;
import java.util.Formatter;
import java.util.Scanner;
import javax.swing.JOptionPane;
public class Main {
static Formatter f;
static String sträng = " ";
static BufferedWriter output;
static File file;
static int nummer = 1;
static int counter = 0;
static private StringBuffer strBuff;
static InputStream is;
static FileWriter fw;
/**
* #param args the command line arguments
*/
public static void main(String[] args) throws Exception {
createFile();
addResponses(file);
readFile(file);
}
public static int addResponse() {
if (nummer == 6) {
try {
output.close();
} catch (IOException ex) {
JOptionPane.showMessageDialog(null, ex.getMessage());
}
System.exit(0);
}
sträng = JOptionPane.showInputDialog("Numbers 1-5 to number " + nummer");
try {
return Integer.parseInt(sträng);
} catch (NumberFormatException f) {
return 6;
}
}
public static File createFile() {
try {
file = new File("numbers.txt");
f = new Formatter(file);
f.close();
} catch (SecurityException se) {
System.err.println("You dont have write access to this file");
System.exit(1);
} catch (Exception ex) {
System.err.println("Error opening or creating file");
System.exit(1);
}
return file;
}
public static void readFile(File x) {
try {
x = new File("numbers.txt");
Scanner in = new Scanner(x);
while (in.hasNextLine()) {
System.out.println(in.nextLine());
}
in.close();
} catch (Exception e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
}
public static void addResponses(File f) throws IOException {
try {
fw = new FileWriter(f, true);
output = new BufferedWriter(fw);
int x = addResponse();
if (nummer == 1) {
output.write(String.format("%s%10s\n", "Rating", " Frequency"));
}
while (x != -1) {
if (x > 0 && x < 6) {
output.write(String.format("%s%10s\n", nummer, sträng));
nummer++;
} else {
JOptionPane.showMessageDialog(null, "Input only numbers between 1-5");
}
x = addResponse();
}
output.close();
} catch (IOException io) {
JOptionPane.showMessageDialog(null, "Wrong");
}
}
}

after playing around with the code, I found out that in your addResponse() method , you have added System.exit(0); so baiscally program was terminating. I've change it to return -1 and it seems to be working.
by the way, this is a very bad coding practice, each method should do stuff seperately regarless of other method. in your case everything is so integerated that is very hard to root the problem. I recommend you looking at some coding convention.
this is how addResponse() method should be working:
public static File createFile() {
try {
file = new File("numbers.txt");
f = new Formatter(file);
f.close();
} catch (SecurityException se) {
System.err.println("You dont have write access to this file");
System.exit(1);
} catch (Exception ex) {
System.err.println("Error opening or creating file");
System.exit(1);
}
return file;
}

Java - Trouble reading CSV to Array

I'm trying to read a .csv file to an array, and then parse the row on commas, to pull out specific numbers from my file. I'm not getting any errors, and the program runs fine, however it won't let me pull from anything other than thisLine[0]. There should be 3 elements in the line.
The csv looks something like this:
32.34553,-122.4535636,-118.1
32.34553,-122.4535536,-118.1
32.34553,-122.4512236,-118.1
32.34553,-122.4515466,-118.1
32.34553,-122.4532336,-118.1
When I try to call thisLine[1] (which should be something like '-122.4535636') I get :
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
at com.mkyong.util.ReadCSV.run(ReadCSV.java:32)
at com.mkyong.util.ReadCSV.main(ReadCSV.java:14)
I'm really new to Java so I'm sorry if this is a simple fix. Thanks for any help,
package com.mkyong.util;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
public class ReadCSV {
public static void main(String[] args) {
ReadCSV obj = new ReadCSV();
obj.run();
}
public void run() {
String csvFile = "C:/Program Files/EDX/Projects/Brisbane, CA R900/Data/GIS/meters.csv";
BufferedReader br = null;
String line = "";
String csvSplitBy = ",";
try {
br = new BufferedReader(new FileReader(csvFile));
while ((line = br.readLine()) !=null) {
String[] thisLine = line.split(csvSplitBy);
System.out.println("The Current Line is: " + thisLine[0] + ", " + thisLine[1]);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (br !=null) {
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
System.out.println("Done");
}
}

ObjectOutputStream, ObjectInputStream, and headers [closed]

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Closed 10 years ago.
I am trying to understand object serialization better, so I am practicing with some code I got from my textbook. (My textbook doesn't explain how to read and write/append objects to a serialization file every time the program starts, which is what I need to do.) I took their program, which just overwrites existing data in a file with the objects from the current session, and add code to it so that it will append the objects and read the whole file instead. I found something really useful here: Appending to an ObjectOutputStream but even if I create a subclass of ObjectOutputStream, override the writeStreamHeader method, and call this subclass if the file already exists, which is what they did, it still throws a CorruptedStreamException. My guess is that I would need to set the pointer back to the beginning of the file, but that doesn't seem to be necessary as there is only one ObjectOutputStream. So, my question is, what else could I possibly need to do?
EDIT: Here is some code.
WriteData.java
import java.io.*;
import java.util.Scanner;
public class WriteData
{
private int number;
private String name;
private float money;
private ObjectInputStream testopen;
private ObjectOutputStream output; //This is for the output. Make sure that
//this object gets an instance of FileOutputStream so that it can write objects
//to a FILE.
private AppendObjectOutputStream appendobjects;
static Scanner input = new Scanner(System.in);
static DataClass d;
public void openfile()
{
//Try opening a file (it must have the ".ser" extension).
try
{
//output = new ObjectOutputStream(new FileOutputStream("test.ser"));
testopen = new ObjectInputStream(new FileInputStream("test.ser"));
}
//If there is a failure, throw the necessary error.
catch (IOException exception)
{
try
{
output = new ObjectOutputStream(new FileOutputStream("test.ser"));
}
catch (FileNotFoundException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
} //end case createfile
if (testopen != null)
{
try
{
testopen.close();
appendobjects = new AppendObjectOutputStream(
new FileOutputStream("test.ser"));
}
catch (FileNotFoundException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public void writedata()
{
//write the data until the user enters a sentry value.
System.out.println("Enter CTRL + z to stop input.\n");
System.out.print ("Enter the data in the following format: " +
"account_number name balance\n->");
while (input.hasNext())
{
System.out.print ("Enter the data in the following format: " +
"account_number name balance\n->");
try
{
number = input.nextInt();
name = input.next();
money = input.nextFloat();
//Make object with that data
d = new DataClass(number, name, money);
//write it to the file
if (output != null)
{
output.writeObject(d);
}
else if (appendobjects != null)
{
appendobjects.writeObject(d);
}
}
catch (IOException e)
{
System.out.println("Error writing to file.");
return;
}
}
System.out.println("\n");
} //end writedata
public void closefile()
{
try
{
if (output != null)
{
output.close();
}
else if (appendobjects != null)
{
appendobjects.close();
}
}
catch (IOException e)
{
System.out.println("Error closing file. Take precautions");
System.exit(1);
}
}
}
DataClass.java
import java.io.Serializable;
public class DataClass implements Serializable
{
private int someint;
private String somestring;
private float somefloat;
public DataClass(int number, String name, float amount)
{
setint(number);
setstring(name);
setfloat(amount);
}
public void setint(int i)
{
this.someint = i;
}
public int getint()
{
return someint;
}
public void setstring(String s)
{
this.somestring = s;
}
public String getstring()
{
return somestring;
}
public void setfloat(float d)
{
this.somefloat = d;
}
public float getfloat()
{
return somefloat;
}
}
AppendObjectOutputStream.java
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.FileOutputStream;
public class AppendObjectOutputStream extends ObjectOutputStream
{
public AppendObjectOutputStream(FileOutputStream arg0) throws IOException
{
super(arg0);
// TODO Auto-generated constructor stub
}
//This is a function that is default in ObjectOutputStream. It just writes the
//header to the file, by default. Here, we are just going to reset the
//ObjectOutputStream
#Override
public void writeStreamHeader() throws IOException
{
reset();
}
}
ReadData.java
import java.io.*;
import java.util.Scanner;
public class ReadData
{
private FileInputStream f;
private ObjectInputStream input; //We should the constructor for this
//object an object of FileInputStream
private Scanner lines;
public void openfile()
{
try
{
f = new FileInputStream("test.ser");
input = new ObjectInputStream (f);
//input.reset();
}
catch (IOException e)
{
e.printStackTrace();
System.exit(1);
}
}
public void readdata()
{
DataClass d;
System.out.printf("%-15s%-12s%10s\n", "Account Number", "First Name",
"Balance");
try
{
while (true)
{
d = (DataClass)input.readObject(); //define d
//read data in from d
System.out.printf("%-15d%-12s%10.2f\n", d.getint(), d.getstring(),
d.getfloat());
}
}
catch (EOFException eof)
{
return;
}
catch (ClassNotFoundException e)
{
System.err.println("Unable to create object");
}
catch (IOException e)
{
e.printStackTrace();
}
}
public void closefile()
{
try
{
if (input != null)
{
input.close();
}
}
catch (IOException ex)
{
System.err.println("Error closing file.");
System.exit(1);
}
}
}
SerializationTest.java
public class SerializationTest
{
public static void main(String[] args)
{
ReadData r = new ReadData();
WriteData w = new WriteData();
w.openfile();
w.writedata();
w.closefile();
r.openfile();
r.readdata();
r.closefile();
}
}

I suggest to do it this way
ObjectOutputStream o1 = new ObjectOutputStream(new FileOutputStream("1"));
... write objects
o1.close();
ObjectOutputStream o2 = new AppendingObjectOutputStream(new FileOutputStream("1", true));
... append objects
o2.close();
it definitely works.

import EJP;
import Evgeniy_Dorofeev;
public class answer
{
private String answera, answerb;
public answer(String a, String b)
{
answera = a;
answerb = b;
}
public void main(String[] args)
{
answer(EJP.response(), Evgeniy_Dorofeev.response());
System.out.println(answera + '\n' + answerb);
}
}

You need to add a 'true' for the append parameter of new FileOutputStream() in the case where you are appending. Otherwise you aren't. Appending, that is.

Using IO Streams in Java

I need to launch a binary file using Java and then interact with it using input and output streams. I've written a prototype to figure out how it works, but so far the only output I'm getting has been null. When run on its own however the child program produces output. What am I doing wrong?
import java.io.*;
public class Stream {
public static void main(String args[]) {
Process SaddleSumExec = null;
BufferedReader outStream = null;
BufferedReader inStream = null;
try {
SaddleSumExec = Runtime.getRuntime().exec("/home/alex/vendor/program weights.txt list.txt");
}
catch(IOException e) {
System.err.println("Error on inStream.readLine()");
e.printStackTrace();
}
try {
inStream = new BufferedReader(new InputStreamReader
(SaddleSumExec.getInputStream()));
System.out.println(inStream.readLine());
}
catch(IOException e){
System.out.println("Error.");
}
}
}

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
public class Prompt {
//flag to end readers and writer
boolean processEnd = false;
public static void main(String[] args) {
new Prompt();
}
public Prompt() {
Process SaddleSumExec = null;
Input in = new Input(this);
Output out = new Output(this);
Input err = new Input(this);
//thread to read a write console
Thread t1 = new Thread(in);
Thread t2 = new Thread(out);
Thread t3 = new Thread(err);
try {
SaddleSumExec = Runtime
.getRuntime()
.exec(
"ConsoleApplication1/bin/Debug/ConsoleApplication1");
in.input = SaddleSumExec.getInputStream();
err.input = SaddleSumExec.getErrorStream();
out.out = SaddleSumExec.getOutputStream();
t2.start();
t1.start();
t3.start();
SaddleSumExec.waitFor();
processEnd = true;
} catch (IOException e) {
System.err.println("Error on inStream.readLine()");
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public boolean isProcessEnd() {
return processEnd;
}
public void setProcessEnd(boolean processEnd) {
this.processEnd = processEnd;
}
/*Readers of Inputs*/
class Input implements Runnable {
private BufferedReader inStream;
InputStream input;
Prompt parent;
public Input(Prompt prompt) {
// TODO Auto-generated constructor stub
parent = prompt;
}
public void run() {
inStream = new BufferedReader(new InputStreamReader(input));
while (!parent.isProcessEnd()) {
try {
String userInput;
while ((userInput = inStream.readLine()) != null) {
System.out.println(userInput);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
/*Writers of Output*/
class Output implements Runnable {
OutputStream out;
Prompt parent;
public Output(Prompt prompt) {
parent = prompt;
// TODO Auto-generated constructor stub
}
#Override
public void run() {
while (!parent.isProcessEnd()) {
try {
String CurLine = "";
InputStreamReader converter = new InputStreamReader(
System.in);
BufferedReader in = new BufferedReader(converter);
while (!(CurLine.equals("quit"))) {
CurLine = in.readLine();
if (!(CurLine.equals("quit"))) {
out.write((CurLine + "\n").getBytes());
out.flush();
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}

You don't seem to be waiting for the child process to end so it is possible that the parent process ends before it gets a chance to read the output stream.
Here is an old but excellent article around Runtime.exec
http://www.javaworld.com/jw-12-2000/jw-1229-traps.html
The correct implementation is on this page
http://www.javaworld.com/jw-12-2000/jw-1229-traps.html?page=4

From what I can tell - there could be two problems here :
Are you trying to obtain the access to the stream BEFORE the child program has started reading ?
Are you running the parent process with insufficient access rights?

If you read a null from readLine() it means the peer has closed the stream. There was no output.