Re: merging equal code (exercise in refactoring)

Eric Sosman <Eric.Sosman@sun.com> writes:


  This answer is better than my own, because it requires
  the least amount of work of the programmer.

  When a list is copied to an array or an array is copied
  to a list, this needs O(n) operations. Therefore, I have
  hesitated to use this myself. But a programmer's time
  usually is more expensive than a processor's time.

  My own solution tries to avoid an additional copy operation.

  The code given was like

public static java.lang.CharSequence format
( PARAMETERS )
{ PREPARATION
  for( LOOP_CONTROL )LOOP_STATEMENT
  COMPLETION }

  The ?LOOP_CONTROL? varied with ?PARAMETERS?, while
  ?PREPARATION?, ?LOOP_STATEMENT? and ?COMPLETION?
  did not change.

  When something varies with a parameter, the usual
  solution is to make this a parameter, too.

  But in Java, the LOOP_CONTROL of a for(:) statement
  can not be used as a parameter (it would have to be
  something like ?quoted code?).

  So one has to invert the usual procedure and to make
  everything else /except/ the loop control the ?parameter?.

  This can be done by creating an object for the
  PREPARATION, LOOP_STATEMENT and COMPLETION.

  Then the two redundant method declarations become:

public static java.lang.CharSequence format
( LIST_PARAMETER )
{ final Delegate delegate = new Delegate();
  for( LIST_LOOP_CONTROL )delegate.loopStatement( /* ... */ );
  return delegate.completion(); }

public static java.lang.CharSequence format
( ARRAY_PARAMETER )
{ final Delegate delegate = new Delegate();
  for( ARRAY_LOOP_CONTROL )delegate.loopStatement( /* ... */ );
  return delegate.completion(); }

  There still is some redundancy, but most of the formerly
  duplicate code now has a single position within the
  declaration of the Delegate class.

  The actual code is following. As an additional benefit,
  the code now is split into more method declarations
  than before, which gives more anchor points for documentation.

class Util
{
  public static java.lang.String indent( final java.lang.String text )
  { final java.lang.String text1 = text.replaceAll( "\n", "\n " );
    return text1; }

  public static java.lang.CharSequence format
  ( final java.lang.CharSequence[] source )
  { final Util util = new Util();
    for( final java.lang.CharSequence component : source )
    util.process( component );
    return util.complete(); }

  public static java.lang.CharSequence format
  ( final java.util.List<java.lang.CharSequence> source )
  { final Util util = new Util();
    for( final java.lang.CharSequence component : source )
    util.process( component );
    return util.complete(); }

  private final java.lang.StringBuilder result;
  private final java.lang.StringBuilder text;
  private boolean first;
    
  public Util()
  { this.result = new java.lang.StringBuilder();
    this.result.append( "Listing:\n" );
    this.text = new java.lang.StringBuilder();
    this.text.append( "[ " );
    this.first = true; }

  public void process( final java.lang.CharSequence component )
  { if( this.first )this.first = false;
    else this.text.append( "\n" );
    this.text.append( component ); }

  public java.lang.CharSequence complete()
  { final char last = this.text.charAt( this.text.length() - 1 );
    boolean space = true;
    switch( last ){ case ' ': case ']': space = false; }
    this.text.append( space ? " ]" : "]" );
    this.result.append( indent( this.text.toString() ));
    return result; }}