自定义iterator 利用增强for循环实现文件行的读取

package cn.niki.fordemo;

import java.util.Iterator;

//这个类提供了文本文件的包装器，在遍历它的时候，它可以列出文件中的每一行

public class TextFile implements Iterable<String> {

private String filename;
public TextFile(String filename) {
this.filename = filename;
}
// one method of the Iterable interface
@Override
public Iterator<String> iterator() {
return new TextFileIterator(filename);
}

}

package cn.niki.fordemo;

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

public class TextFileIterator implements Iterator<String> {

// stream being read from
BufferedReader in;
// return value of next call to next()
String nextline;

// the structure method of TextFileItrator
public TextFileIterator(String filename) {
// 打开文件并读取第一行 如果第一行存在获得第一行
try {
in = new BufferedReader(new FileReader(filename));
nextline = in.readLine();
} catch (IOException e) {
e.printStackTrace();
}
}

// if the next line is non-null then we have a next line
@Override
public boolean hasNext() {
return nextline != null;
}

// return the next line,but first read the line that follows it
@Override
public String next() {
try {
String result = nextline;
//if we dont have reached EOF yet
if (nextline != null) {
nextline = in.readLine(); // read another line
if (nextline == null)
in.close(); // and close on EOF
}
return result;
} catch (IOException e) {
throw new IllegalArgumentException(e);
}
}
// we dont need remove the line just read it
@Override
public void remove() {
throw new UnsupportedOperationException();
}

public static void main(String[] args){
String filename="C://mail.txt";
//使用增强for循环进行文件的读取
for(String line:new TextFile(filename)){
System.err.println(line);
}

}
}