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How to input and output from/or to a file?!

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How to input and output from/or to a file?!

Oct 29th, 2009

Hi mates..

I'm trying to find a way in how to inputing or outputting from a file in Java.

For my bad luck when I finished my Java course, our professor didn't talked about this thing.

I searched in the internet, and found a way in inputing from a file which is:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
import java.io.File;
import java.io.FileNotFoundException;
try {
			Scanner input = new Scanner(new File("file.txt"));
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
import java.io.File;
import java.io.FileNotFoundException;
try {
			Scanner input = new Scanner(new File("file.txt"));
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

but after that, how to read the content of that file! also, if the file has a paragraph how can I search for a specific words, I think in java I can only read a line not a word!

for example "a" or "if" or "playing" how can I look for them if they exist in the file or not.

After that, how to output the data I want in an output file!

Thanks in advance.

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Posting Virtuoso

Oct 29th, 2009

First of all check the Scanner API. You found a code and you didn't think to check the API.

Now, there is the nextLine method that reads the next line of the file. Combine it with the has.. methods to read the entire file:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
while (scanner.hasNextLine() ) {
   String line = scanner.nextLine();
 
// check if the line contains the words you want
int i = line.indexOf("if");
// if i==-1 then not found
}
while (scanner.hasNextLine() ) {
   String line = scanner.nextLine();

// check if the line contains the words you want
int i = line.indexOf("if");
// if i==-1 then not found
}

You can store the entire file in a Vector(add each line to a vector as the loop runs) and then loop through the vector to find the words you are looking for. Or you can check the line as you read it.
You might want to use the method: String.indexOf(String s)
It will return -1 if the argument is not found (check the String API)

OR
For a more sophisticated way, use regular expressions and patterns with these methods:
http://java.sun.com/j2se/1.5.0/docs/...a.lang.String)
or
findInLine

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Posting Virtuoso

Oct 29th, 2009

If you want to find a specific word from within a file, another way to do it would be to use Scanner's next() method, then use String.equals to see if they match.

Out.

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Posting Virtuoso

Oct 29th, 2009

•

Originally Posted by BestJewSinceJC

If you want to find a specific word from within a file, another way to do it would be to use Scanner's next() method, then use String.equals to see if they match.

Actually my solution is not correct. If a word contains the argument then it will return that it found it, even though it is not a whole word but only a part of it.

In order for my solution to work, the OP would have to use the .split(" ") method to "break" the line and then use the equals method the way you described.

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Join Date: Jun 2008

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Q8iEnG

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Oct 29th, 2009

Thanks mates for those useful links.

Sorry for that but I got confused, so which solution you think it'll be easier to implement and as you said javaAddict I want to find the WHOLE word if exist not a part of it.

like for example when I search for "ok" it wouldn't take this as a found "okay".

Thanks

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Posting Virtuoso

Oct 29th, 2009

http://java.sun.com/j2se/1.5.0/docs/...l/Scanner.html

Using next() is the easiest way to go and will work for what you are describing. And I'm linking to the documentation because if you read the method description for next(), it will become clear what the method does. Alternatively, you could create a while loop

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
while(scanner.hasNext()) System.out.println(scanner.next());
while(scanner.hasNext()) System.out.println(scanner.next());

And just look at what it prints to answer your question.

Out.

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Oct 30th, 2009

•

Originally Posted by BestJewSinceJC

http://java.sun.com/j2se/1.5.0/docs/...l/Scanner.html

Using next() is the easiest way to go and will work for what you are describing. And I'm linking to the documentation because if you read the method description for next(), it will become clear what the method does. Alternatively, you could create a while loop
Help with Code Tags

Java Syntax (Toggle Plain Text)
 
while(scanner.hasNext()) System.out.println(scanner.next());
while(scanner.hasNext()) System.out.println(scanner.next());
And just look at what it prints to answer your question.

WOW, thank you so much I'm now coding easily

one more thing please, if I want to check a specific word where it occurred in which line of the file, how to do that?

I mean for example "a" I want to see in which line it appears, how to do that!?

Thanks in advance.

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Q8iEnG

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Oct 30th, 2009

This is my code now, WHY i'm getting an error!!

Here is the Data.java:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
 
public class Data {
 
	private String[] a = {"a", "if", "is", "of", "peck", "peppers", "peter", "picked", "pickled", "piper", "that", "the", "where"};
	private int Freq[] = new int[50];
 
	public int[] getFreq() {
		return Freq;
	}
	public void setFreq(int[] f) {
		Freq = f;
	}
 
	public void searchForFreq()
	{
			Scanner input;
			try {
				input = new Scanner(new File("file.txt"));
			} catch (FileNotFoundException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			while( input.hasNext() )
				{
				if( input.next() == "a")
					Freq[0] = Freq[0] + 1;
				else
					if( input.next() == "if")
						Freq[1] = Freq[1] + 1;
					else
						if( input.next() == "is")
							Freq[2] = Freq[2] + 1;
						else
							if( input.next() == "of")
								Freq[3] = Freq[3] + 1;
							else
								if( input.next() == "peck")
									Freq[4] = Freq[4] + 1;
								else
									if( input.next() == "peppers")
										Freq[5] = Freq[5] + 1;
									else
										if( input.next() == "peter")
											Freq[6] = Freq[6] + 1;
										else
											if( input.next() == "picked")
												Freq[7] = Freq[7] + 1;
											else
												if( input.next() == "pickled")
													Freq[8] = Freq[8] + 1;
												else
													if( input.next() == "piper")
														Freq[9] = Freq[9] + 1;
													else
														if( input.next() == "that")
															Freq[10] = Freq[10] + 1;
														else
															if( input.next() == "the")
																Freq[11] = Freq[11] + 1;
															else
																if( input.next() == "where")
																	Freq[12] = Freq[12] + 1;
				}
			for( int i = 0; i < Freq.length; i++ )
			{
				System.out.println( a[i] + "...." + Freq[i]);
			}
 
	}
 
 
}
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class Data {
		
	private String[] a = {"a", "if", "is", "of", "peck", "peppers", "peter", "picked", "pickled", "piper", "that", "the", "where"};
	private int Freq[] = new int[50];
	
	public int[] getFreq() {
		return Freq;
	}
	public void setFreq(int[] f) {
		Freq = f;
	}
	
	public void searchForFreq()
	{
			Scanner input;
			try {
				input = new Scanner(new File("file.txt"));
			} catch (FileNotFoundException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			while( input.hasNext() )
				{
				if( input.next() == "a")
					Freq[0] = Freq[0] + 1;
				else
					if( input.next() == "if")
						Freq[1] = Freq[1] + 1;
					else
						if( input.next() == "is")
							Freq[2] = Freq[2] + 1;
						else
							if( input.next() == "of")
								Freq[3] = Freq[3] + 1;
							else
								if( input.next() == "peck")
									Freq[4] = Freq[4] + 1;
								else
									if( input.next() == "peppers")
										Freq[5] = Freq[5] + 1;
									else
										if( input.next() == "peter")
											Freq[6] = Freq[6] + 1;
										else
											if( input.next() == "picked")
												Freq[7] = Freq[7] + 1;
											else
												if( input.next() == "pickled")
													Freq[8] = Freq[8] + 1;
												else
													if( input.next() == "piper")
														Freq[9] = Freq[9] + 1;
													else
														if( input.next() == "that")
															Freq[10] = Freq[10] + 1;
														else
															if( input.next() == "the")
																Freq[11] = Freq[11] + 1;
															else
																if( input.next() == "where")
																	Freq[12] = Freq[12] + 1;
				}
			for( int i = 0; i < Freq.length; i++ )
			{
				System.out.println( a[i] + "...." + Freq[i]);
			}
		
	}
	

}

and this is Driver.java:

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 Java Syntax (Toggle Plain Text) 
public class Driver {
 
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
 
		Data d = new Data();
		d.searchForFreq();
 
 
 
	}
 
}
public class Driver {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		Data d = new Data();
		d.searchForFreq();
		
		

	}

}

any clue on how to solve the error?

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Join Date: Dec 2007

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Posting Virtuoso

Oct 30th, 2009

First of all run this code:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
while(scanner.hasNext()) {
     System.out.println(scanner.next());
}
while(scanner.hasNext()) {
     System.out.println(scanner.next());
}

The name of the method is pretty self explanatory:
Whenever you call it it returns the next word.
In your while loop you keep calling it again and again inside the loop so every time you get the next word. This doesn't compare the same word:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
if( input.next() == "a") // this will return a word
					Freq[0] = Freq[0] + 1;
				else
					if( input.next() == "if") // this will return a different word from the previous one
						Freq[1] = Freq[1] + 1;
if( input.next() == "a") // this will return a word
					Freq[0] = Freq[0] + 1;
				else
					if( input.next() == "if") // this will return a different word from the previous one
						Freq[1] = Freq[1] + 1;

Also use the equals method to compare objects such as the String object:
if ( s.equals("a") ) { .. }

Last edited by javaAddict; Oct 30th, 2009 at 9:09 am.

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Join Date: Jun 2008

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Reputation: Q8iEnG is an unknown quantity at this point

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Q8iEnG

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#10

Oct 30th, 2009

•

Originally Posted by javaAddict

First of all run this code:
Help with Code Tags

Java Syntax (Toggle Plain Text)
while(scanner.hasNext()) {
     System.out.println(scanner.next());
}
while(scanner.hasNext()) { System.out.println(scanner.next()); }
The name of the method is pretty self explanatory:
Whenever you call it it returns the next word.
In your while loop you keep calling it again and again inside the loop so every time you get the next word. This doesn't compare the same word:
Help with Code Tags

Java Syntax (Toggle Plain Text)
if( input.next() == "a") // this will return a word
					Freq[0] = Freq[0] + 1;
				else
					if( input.next() == "if") // this will return a different word from the previous one
						Freq[1] = Freq[1] + 1;
if( input.next() == "a") // this will return a word Freq[0] = Freq[0] + 1; else if( input.next() == "if") // this will return a different word from the previous one Freq[1] = Freq[1] + 1;
Also use the equals method to compare objects such as the String object:
if ( s.equals("a") ) { .. }

ahaaa omg i messed around lol

So, you mean I should first save the input in a variable and compare it
like this:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
String s = input.next();
if( s.equals("a") )
blah blah
else if( s.equals("if") )
blah blah
...
String s = input.next();
if( s.equals("a") )
blah blah
else if( s.equals("if") )
blah blah
...

That is what you meant?

And yeah I ran this code:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
while(scanner.hasNext()) {
     System.out.println(scanner.next());
}
while(scanner.hasNext()) {
     System.out.println(scanner.next());
}