Looping through a text file with an iterator

[Carey Brown]

Just thought somebody might find this interesting/useful.
I wanted to use the new 'for' syntax to loop through all the lines in a text file; something I find myself doing quite often.

A simple example:

for( String s : new FileLineIterable(filename) )
    System.out.println( s );

It required making two classes: FileLineIterable, and FileLineIterator.
You might find this useful as an example for implementing your own iterator class.

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;

/**
 * The purpose of a <code>FileLineIterable</code> is to supply an iterator that
 * will return each line of a text file as a String. This can be used in
 * conjunction with the new (Java1.5) 'foreach' syntax.<BR>
 * Example:
 * <PRE>
 * 		for( String s : new FileLineIterable( filename ) )
 *			System.out.println( s );
 * </PRE>
 *
 * @author Carey Brown
 */
public class FileLineIterable
implements Iterable<String>
{
	private File			file;

	/**
	 * Test main() and an example of using FileLineIterable class.
	 * @param args
	 */
	public static void main( String[] args )
	{
		try
		{
			for( String s : new FileLineIterable( args[0] ) )
				System.out.println( s );
		}
		catch( Exception ex )
		{
			ex.printStackTrace();
		}
	}

	public FileLineIterable( String fileName )
	throws IOException
	{
		this( new File( fileName ) );
	}

	public FileLineIterable( File file ) throws IOException
	{
		if( ! file.exists() )
			throw new FileNotFoundException( "File does not exist: " + file.getPath() );
		if( ! file.isFile() )
			throw new IOException( "File is not of type 'file': " + file.getPath() );
		this.file = file;
	}

	public FileLineIterator iterator()
	{
		try
        {
	        return new FileLineIterator( file );
        }
        catch( IOException e )
        {
	        e.printStackTrace();
	        return null;
        }
	}
}

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
import java.util.NoSuchElementException;


public class FileLineIterator
implements Iterator<String>
{
	private FileReader		reader;
	private BufferedReader	in = null;
	private String			string = null;

	public FileLineIterator( File file )
	throws IOException
	{
		try
		{
			reader		= new FileReader( file );
			in			= new BufferedReader( reader );
			string		= in.readLine();
			if( string == null )
			{
				in.close();
				in = null;
			}
		}
		catch( IOException ex )
		{
			string = null;
			if( in != null ) try{ in.close(); } catch( IOException ex2 ) { }
			in = null;
			throw ex;
		}
	}

	@Override
    public boolean hasNext()
    {
		return string != null;
    }

	@Override
    public String next()
	throws NoSuchElementException
    {
		String		returnString = string;
		try
		{
			if( string == null )
			{
				throw new NoSuchElementException( "Next line is not available" );
			}
			else
			{
				string = in.readLine();
				if( string == null && in != null )
				{
					in.close();
					in = null;
				}
			}
		}
		catch( Exception ex )
		{
			throw new NoSuchElementException( "Exception caught in FileLineIterator.next() " + ex );
		}
		return returnString;
    }

	@Override
    public void remove()
    {
		throw new UnsupportedOperationException( "FileLineIterator.remove() is not supported" );
    }

	@Override
    protected void finalize()
	throws Throwable
	{
		try
		{
			string = null;
			if( in != null ) try{ in.close(); } catch( Exception ex ) { }
			in = null;
		}
		finally
		{
			super.finalize();
		}
	}
}