迭代器用Java读取和处理文件 [英] Iterators to read and process file in Java

问题描述

假设我有一个类 Point 和一个函数来处理 Point 实例

 
 class Point {private final int x，y; ...} 
 ... 
 void handlePoints（Iterable  points）{for（Point p：points）{...}} 
 

现在我想从文件中读取 points 。该文件的每一行都包含两个数字，所以我有一个函数（工厂方法）来创建一个点从一个线。

 
 Point makePoint（String line）{...} 
 

我应该怎么做现在？我可以写一个函数来读取文件到 points 列表并调用 handlePoints 函数。

 
 List< Point> readPoints（BufferedReader reader）{...} //在这里使用makePoint 
 
 void handlePoints（BufferedReader reader）{
 List< Point> points = readPoints（阅读器）; 
 handlePoints（points）; 
 
 

不幸的是，这个函数看起来并不是特别优雅，因为它在内存中创建了一个不必要的点列表。

使用迭代器会更好吗？

 
 void handlePoints（Iterator< Point> points）{...} 
 
 Iterator< Point> readPoints（BufferedReader reader）{...} //在这里使用makePoint 
 
 void handlePoints（BufferedReader reader）{
 Iterator< Point> points = readPoints（阅读器）; 
 handlePoints（points）; 
} 
 

有意义吗？如果你不需要把所有的点都放在内存中，那么这个代码在Java中是不是太吵闹了？

，请考虑更多的内容：

  while（reader.ready（））
 {
 String line = reader.readLine（）; 
 Point point = makePoint（line）; 
 handlePoint（point）; 
 
 
 
 
 
 $ b 
如何用迭代器和handlePoints来处理异常被添加）
  class PointIterator实现Iterator< Point> 
 {
 BufferedReader reader; 
 PointIterator（BufferedReader myReader）{reader = myReader; }; 
 @Override 
 public boolean hasNext（）{return myReader.ready（）; }; 
 @Override 
 public Point next（）{return makePoint（myReader.readLine（））; }; 
 @Override 
 public void remove（）
 {throw new UnsupportedOperationException（Remove not supported！）; }; 
 
 code $ 
 
 
 $  handlePoints 需要一个 Iterable ：
  class PointIterable implements Iterable< Point> 
 {
 BufferedReader reader; 
 public PointIterable（BufferedReader myReader）{reader = myReader; }; 
 @Override 
 public Iterator< Point> iterator（）{返回新的PointIterator（reader）; } 
} 
  
使用：
 
 
  handlePoints（new PointIterable（reader））; 
  
 
Suppose I have a class Point and a function to process Point instances
class Point { private final int x, y; ... } 
...
void handlePoints(Iterable<Point> points) { for (Point p: points) {...} }
Now I would like to read points from a file. Each line of the file contains two numbers, so I have a function ("factory method") to create a point from a line.
Point makePoint(String line) { ... }
What should I do now? I can write a function to read the file to a list of points and call the handlePoints function.
List<Point> readPoints(BufferedReader reader) {...} // use makePoint here

void handlePoints(BufferedReader reader) {
   List<Point> points = readPoints(reader); 
   handlePoints(points);
}
Unfortunately this function does not seem particularly elegant since it creates an unnecessary list of points in memory.

Wouldn't it be better to use iterators ? 
void handlePoints(Iterator<Point> points) {...}

Iterator<Point> readPoints(BufferedReader reader) {...} // use makePoint here

void handlePoints(BufferedReader reader) {
   Iterator<Point> points = readPoints(reader); 
   handlePoints(points);
}
Does it make sense? Won't be this code too "noisy" in Java?
解决方案
If you don't need to have all points in memory, think of something more along these lines:
while (reader.ready())
{
  String line = reader.readLine();
  Point point = makePoint(line);
  handlePoint(point);
}
How to do this with an iterator and handlePoints: (code for handling exceptions to be added)
class PointIterator implements Iterator<Point>
{
  BufferedReader reader;
  PointIterator(BufferedReader myReader) { reader = myReader; };
  @Override
  public boolean hasNext() { return myReader.ready(); };
  @Override
  public Point next() { return makePoint(myReader.readLine()); };
  @Override
  public void remove()
  { throw new UnsupportedOperationException("Remove not supported!"); };
}
And because handlePoints takes an Iterable:
class PointIterable implements Iterable<Point>
{
  BufferedReader reader;
  public PointIterable(BufferedReader myReader) { reader = myReader; };
  @Override
  public Iterator<Point> iterator() { return new PointIterator(reader); }
}
To use:
handlePoints(new PointIterable(reader));


                        
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