JAVA 增强for循环

java中的增强for循环可以这样理解：

for (Iterator<
        E> #i = (
        expression).iterator(); #i.hasNext(); ) {

        declaration = #i.next();

        statement
}

例子1

import java.util.*;
public class TenIntegers implements Iterable<Integer> {
　public Iterator<Integer> iterator() {
　　return new Iterator<Integer>() {
　　　private int count = 0;
　　　public boolean hasNext() {
　　　　return (count < 10);
　　　}
　　　public Integer next() {
　　　　return Integer.valueOf(count++);
　　　}
　　　public void remove() {
　　　　throw new UnsupportedOperationException();
　　　}
　　};
　}
　public static void main(String[] args)
　{
　　TenIntegers integers = new TenIntegers();
　　for (int i : integers)
　　{
　　　System.out.println(i);/* 依次输出从“0"到“9”的十个整数 */
　　}
　}
}

例子2：

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 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 being read from
    BufferedReader in;

    // Return value of next call to next()
    String nextline;

    public TextFileIterator() {
      // Open the file and read and remember the first line
      //   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);
  }
}