package com.oreilly.tiger.ch07;
import java.util.Iterator;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
/**
* This class allows line-by-line iteration through a text file.
* The iterator's remove() method throws UnsupportedOperatorException.
* The iterator wraps and rethrows IOExceptions as IllegalArgumentExceptions.
*/
public class TextFile implements Iterable<String> {
// Used by the TextFileIterator class below
final String filename;
public TextFile(String filename) {
this.filename = filename;
}
// This is the one method of the Iterable interface
public Iterator<String> iterator() {
return new TextFileIterator();
}
// This non-static member class is the iterator implementation
class TextFileIterator implements Iterator<String> {
// The stream we're reading from
BufferedReader in;
// Return value of next call to next()
String nextline;
public TextFileIterator() {
// Open the file and read and remember the first line.
// We peek ahead like this for the benefit of hasNext().
try {
in = new BufferedReader(new FileReader(filename));
nextline = in.readLine();
} catch(IOException e) {
throw new IllegalArgumentException(e);
}
}
// If the next line is non-null, then we have a next line
public boolean hasNext() {
return nextline != null;
}
// Return the next line, but first read the line that follows it.
public String next() {
try {
String result = nextline;
// If we haven't reached EOF yet
if (nextline != null) {
nextline = in.readLine(); // Read another line
if (nextline == null)
in.close(); // And close on EOF
}
// Return the line we read last time through.
return result;
} catch(IOException e) {
throw new IllegalArgumentException(e);
}
}
// The file is read-only; we don't allow lines to be removed.
public void remove() {
throw new UnsupportedOperationException();
}
}
public static void main(String[] args) {
String filename = "TextFile.java";
if (args.length > 0)
filename = args[0];
for(String line : new TextFile(filename))
System.out.println(line);
}
}
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