| ption {
// Add some items for good measure
manufacturers.add("Epiphone Guitars");
manufacturers.add("Gibson Guitars");
// Iterate with for/in
for (String manufacturer : manufacturers) {
out.println(manufacturer);
}
}
public static void main(String[] args) {
try {
CustomObjectTester tester = new CustomObjectTester();
tester.testListExtension(System.out);
} catch (Exception e) {
e.printStackTrace();
}
}
}
手动处理遍历
在某些不常见的情况下 —— 老实说，我费了很大劲想到了很多 —— 在您的定制对象可以遍历的时候，您可能需要执行特定的行为。在这些（相当不幸）的情况下，您必须自己处理这些事情。清单 19 演示了如何做，虽然需要做很多工作，但是并不复杂，所以我把代码留给您自己来看。以下这个类提供了文本文件的包装器，在遍历它的时候，它将列出文件中的每行内容。
清单 19. 耐心点，您自己也能实现 Iterable 接口，并在循环中提供定制行为
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;
|
