circularshifter.java

KWIC系统 采用管道/过滤器风格实现

import java.io.IOException;
import java.io.CharArrayWriter;
import java.util.StringTokenizer;


public class CircularShifter extends Filter
{
	public CircularShifter(Pipe input, Pipe output)
	{
    	super(input, output);
	}

    /* Produces all circular shifts of lines from the input pipe. */

    protected void transform(){
    try
    {
      CharArrayWriter writer = new CharArrayWriter();

      int c = input_.read();

      while(c != -1)
      {
        if(((char) c) == '\n')    //if meet the symbol of end of line
        {
          String line = writer.toString();
          StringTokenizer tokenizer = new StringTokenizer(line);  //将String line拆开成单个的词
          String[] words = new String[tokenizer.countTokens()];   //create an array of String
          int i = 0;

          while(tokenizer.hasMoreTokens())        //将String line拆开成单个的词
            words[i++] = tokenizer.nextToken();   // load all words into words[]

          for(i = 0; i < words.length; i++)
          {
            String shift = "";

            // 我们要将所有的数组words中的词words[0], words[1],...,words[words.length-1]
            // 以及他们所有的shifts “连接”到一个大的字符串shift中，并且带有相应的空格
            // when i=0, put all words[0],...,words[words.length-1] into shift
            // when i=1, concate words[1],...,words[words.length-1], words[0] at the end of shift
            // when i=2, concate words[2],...,words[0], words[1] at the end of shift
            // when i=3, concate words[3],...,words[0], words[1], words[2]at the end of shift

            for(int j = i; j < (words.length + i); j++)     //start shifting
            {
              shift += words[j % words.length];
              if(j < (words.length + i - 1))
                shift += " ";
            }

            shift += '\n';    // 添加一个行截止符
            char[] chars = shift.toCharArray();     // 将大字符串shift改成char[]型，叫做chars
            for(int j = 0; j < chars.length; j++)   // 将chars的内容按照字符写入写入到输出数据流
              output_.write(chars[j]);
          }   //end of 1st "for" loop， 完成了将完整的一行字以及以及他们所有的shifts “连接”
              //到一个大的字符传shift中，并且带有相应的空格
          writer.reset();
        }
        else   //对应于if(((char) c) == '\n')
          writer.write(c);   // what to write？？

        c = input_.read();
      }

      output_.closeWriter();
    }
    catch(IOException exc)
    {
      exc.printStackTrace();
      System.err.println("KWIC Error: Could not make circular shifts.");
      System.exit(1);
    }
  }
}