Trying to Read From A File In Java

The Crab

Hello, I'm trying to read from a file in Java but its giving me huge problems. Now with the system.out.println its telling me that there is an error because the system packet doesn't exist.

import java.io.*;

public class ClockAssignment {

    public static void main (String[] args) {

int sec, min, hour, aSec, aMin, aHour;    
	
	try{

		FileInputStream filestream = new FileInputStream ("clock.dat");
		
		ObjectInputStream os = new ObjectInputStream (filestream);
		
		Object one = os.readObject();
		Object two = os.readObject();
		Object three = os.readObject();
		Object four = os.readObject();
		Object five = os.readObject();
		Object six = os.readObject();

		int sec = (int)one;
		int min = (int)two;
		int hour = (int)three;
		int aSec = (int)four;
		int aMin = (int)five;
		int aHour = (int)six;
	
os.close();
	} catch(Exception ex) {
	ex.printStackTrace();
	}
	system.out.println (sec + min + hour + aSec + aMin + aHour);
    }

}

moycullen14

The Crab wrote: »

Hello, I'm trying to read from a file in Java but its giving me huge problems. Now with the system.out.println its telling me that there is an error because the system packet doesn't exist.

import java.io.*;

public class ClockAssignment {

    public static void main (String[] args) {

int sec, min, hour, aSec, aMin, aHour;    
	
	try{

		FileInputStream filestream = new FileInputStream ("clock.dat");
		
		ObjectInputStream os = new ObjectInputStream (filestream);
		
		Object one = os.readObject();
		Object two = os.readObject();
		Object three = os.readObject();
		Object four = os.readObject();
		Object five = os.readObject();
		Object six = os.readObject();

		int sec = (int)one;
		int min = (int)two;
		int hour = (int)three;
		int aSec = (int)four;
		int aMin = (int)five;
		int aHour = (int)six;
	
os.close();
	} catch(Exception ex) {
	ex.printStackTrace();
	}
	system.out.println (sec + min + hour + aSec + aMin + aHour);
    }

}

A few problems here:

Your problem with sec, min, etc is that they're declared twice. First in main() and second within the try { }. Change int sec = (int)one; to sec = (int)one will fix that

Next, it should be System.out.println, not system.out.println

Now for the big problem.

You are assuming that your file consists of 6 integers, so read 6 integers. reading an object is no good, you have to tell it the type. You can do either:

Integer intObj = os.readInt();

or

Integer intObj = (Integer)os.readObject();

and then

int prim = intObj.intValue(); // get the int primitive value of Integer Object

You must understand those two statements. Integer is an Object, int is a primitive. That's a very important distinction.

What you are doing is reading a file of Objects, not primitives, that was created by java - serialized in other words. Really you should start with the code that writes the file and the reading is then the reverse operation.

Hope this helps.

Other things to think about are what if the file does not contain 6 Integer objects?

Wouldn't it be better is the file contained one object that itself contained 6 Integer objects? That way the read check would only have to be done once.

Stick with it, it'll come....

The Crab

Thanks, I've done all that.

They told us to keep it as six integers as the file only contains six. I understand your point and agree with you but unfortunately their rules are otherwise.

Now it gives me a problem at runtime - I attached the screen because I really don't understand what's going on.

lynchie

Where did clock.dat come from? Who created it? Can you verify that the data in the file is correct. Java is throwing the exception as data in the file does not conform to its consistency checks.

The Crab

lynchie wrote: »

Where did clock.dat come from? Who created it? Can you verify that the data in the file is correct. Java is throwing the exception as data in the file does not conform to its consistency checks.

The college created it. I saved it into the same folder. It does look weird though as the file seems to have the icon of a windows media player file. When I opened it in its zipped format it showed six number.

Just checked and it actually describes itself as a Video CD Movie. Opening it with Notepad++ does however still show the six numbers.

moycullen14

As we have said, you really need to know HOW the file was created.

An ObjectInputStream can only be used to read a stream created by ObjectOutputStream - which puts a header in the file to tell whats in it, what Objects. What you perhaps need to use is DataInputStream, for example.


DataInputStream dis = new DataInputStream(new FileInputStream ("clock.dat"));
int sec = dis.readInt();
etc, etc

Have a look at http://www.kodejava.org/examples/214.html, it shows how to use DataInput/OutputStreams together. The important thing is you use the SAME code to read as was used to write.

ObjectInput/OutputStream is used for complex objects that can be written/read in one operation. DataInput/OutputStream is used for primitive (i.e. int, float, char) datatypes. I'd say if you change your code to use DIS it'll work fine.

The Crab

Thanks, I tried to follow something along those lines but it still tells me java.io.EOFException

at java.io.DataInputStream.readInt (DataInputStream.java:392)
at ClockAssignment.main(ClockAssignment.java:25)
2038387793

Please help. I've tried contacting my lecturer in every which way and he seems to have no interest in getting back to me.

import java.io.*;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;

public class ClockAssignment {

    public static void main (String[] args) {
    
	int sec = 0; 
	int min = 0; .
	int hour = 0; 
	int aSec = 0;
	int aMin = 0; 
	int aHour = 0;;
	
	try{

		DataInputStream dis = new DataInputStream (new FileInputStream ("clock.dat"));
		
		sec = dis.readInt();
		min = dis.readInt();
		hour = dis.readInt();
		aSec = dis.readInt();
		aMin = dis.readInt();
		aHour = dis.readInt();
	
dis.close();
	} catch(Exception ex) {
	ex.printStackTrace();
	}
	System.out.println (sec + min + hour + aSec + aMin + aHour);
    }

}

moycullen14

What's happening is you're reading beyond the end of the file. You're trying to read 6 integers (say 24 bytes) and the file isn't that big. Maybe the sec, hour and minute are stored as Bytes? (hour, min & sec)

How big is the file?

Can you put it online somewhere?

Can you provide a hex dump(http://www.richpasco.org/utilities/hexdump.html) of the file?

Put the following lines in your program:

System.out.println("sec = " + sec); // and so on....

After each readInt and see what happens

onemorechance

The Crab wrote: »

Thanks, I tried to follow something along those lines but it still tells me java.io.EOFException

at java.io.DataInputStream.readInt (DataInputStream.java:392)
at ClockAssignment.main(ClockAssignment.java:25)
2038387793

Please help. I've tried contacting my lecturer in every which way and he seems to have no interest in getting back to me.

http://docs.oracle.com/javase/6/docs/api/java/io/DataInputStream.html#readInt()

readInt

public final int readInt()
throws IOException
See the general contract of the readInt method of DataInput.
Bytes for this operation are read from the contained input stream.

Specified by:
readInt in interface DataInput
Returns:
the next four bytes of this input stream, interpreted as an int.
Throws:
EOFException - if this input stream reaches the end before reading four bytes.
IOException - the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
See Also:
FilterInputStream.in

The Crab

I changed it to bytes. Now there is no runtime error but it produces 142 instead of 0 0 0 5 23 15 ???

When I tried to read just the first int it returns 806160944.

I'm so frustrated. AAARRRGGGHHHHH .

moycullen14

The Crab wrote: »

I changed it to bytes. Now there is no runtime error but it produces 142 instead of 0 0 0 5 23 15 ???

When I tried to read just the first int it returns 806160944.

I'm so frustrated. AAARRRGGGHHHHH .

Answer the questions I posed above

RealistSpy

I have a java Io library if you want to try that. Might make things easier for you.

/portfolio/java-projects/java-library

The Crab

Thanks to everyone. I used a lot of your advice and finally found a way around it with java scanner. I am completely useless at this stuff so having help on here is great !