字符串反转-单词本身不反转

测试程序：
import static org.junit.Assert.assertEquals;

import org.junit.Test;

public class ReverseTest
{

  @Test
  public void testNormalSentence()
  {
    assertEquals( new ConcurrentReverse( "Hello Peter Sunny Leaf" ).reverse(), "Leaf Sunny Peter Hello" );
  }

  @Test
  public void testEmptySentence()
  {
    assertEquals( new ConcurrentReverse( "" ).reverse(), "" );
  }

  @Test
  public void testSpaceSentence()
  {
    assertEquals( new ConcurrentReverse( "   " ).reverse(), "   " );
  }

  @Test
  public void testMultipleSpaceSentence()
  {
    assertEquals( new ConcurrentReverse( " 123  345  " ).reverse(), "  345  123 " );
  }

  @Test
  public void testSentenceWithSpacePrefix()
  {
    assertEquals( new ConcurrentReverse( " 123 456" ).reverse(), "456 123 " );
  }

  @Test
  public void testSentenceWithSpaceSuffix()
  {
    assertEquals( new ConcurrentReverse( "123 456 " ).reverse(), " 456 123" );
  }

  @Test
  public void testSentenceWithSpaceDoubleEnded()
  {
    assertEquals( new ConcurrentReverse( " 123 , 456 " ).reverse(), " 456 , 123 " );
  }

}



主程序：
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;
import java.util.concurrent.TimeUnit;

public class ConcurrentReverse
{

  private final static char SEPERATOR = ' ';

  private StringBuilder sentence;

  private ForkJoinPool exetutor;

  ConcurrentReverse( String sentence )
  {
    this.sentence = new StringBuilder( sentence );
    this.exetutor = new ForkJoinPool();
  }

  class ReverseTask extends RecursiveAction
  {
    private static final long serialVersionUID = 1L;

    private int from;
    private int to;

    ReverseTask( int from, int to )
    {
      this.from = from;
      this.to = to;
    }

    @Override
    protected void compute()
    {
      reverse_word( from, to );
    }
  }

  /**
   * Algorithm => reverse the whole String and then each word
   *
   * @return the reversed string
   * @throws InterruptedException
   */
  public String reverse()
  {

    // Reverse the whole string first, the internal string will be replace with the inverse one
    sentence.reverse();

    // Reverse each word separated by the SEPERATOR
    for ( int j = 0, i = 0; j <= sentence.length(); j++ )
    {
      if ( j == sentence.length() || SEPERATOR == sentence.charAt( j ) )
      {
        if ( j != i )
        {
          exetutor.submit( new ReverseTask( i, j - 1 ) );
        }
        i = j + 1;
      }

    }

    // Wait all tasks to finish word level inversion
    try
    {
      exetutor.shutdown();
      exetutor.awaitTermination( 1, TimeUnit.DAYS );
    }
    catch ( InterruptedException e )
    {
      e.printStackTrace();
    }
    return sentence.toString();

  }

  private void reverse_word( int from, int to )
  {
    for ( ; from < to; from++, to-- )
    {
      swap( from, to );
    }
  }

  private void swap( int a, int b )
  {
    char a_value = sentence.charAt( a );
    char b_value = sentence.charAt( b );

    sentence.setCharAt( a, b_value );
    sentence.setCharAt( b, a_value );
  }
}