StripIterator.java :  » Template-Engine » stringtemplate » org » antlr » stringtemplate » language » Java Open Source

package org.antlr.stringtemplate.language;

import java.util.Iterator;

/** Given an iterator, return only the non-null elements via next(). */
public class StripIterator implements Iterator {
  protected Iterator it;

  /** To know if stripped iterator hasNext(), we need to see if there
   *  is another non-null element or not.
   */
  protected Object lookahead;

  public StripIterator(Iterator it) {
    this.it = it;
    consume(); // prime lookahead
  }

  /** Set lookahead to next non-null element or null if nothing left */
  protected void consume() {
    if ( !it.hasNext() ) {
      lookahead = null;
      return;
    }
    Object e = null;
    // scan for next non-null value
    while ( e==null && it.hasNext() ) {
      e = it.next();
    }
    lookahead = e;
  }

  /** Either the list has more stuff or our lookahead has last element */
  public boolean hasNext() {
    return lookahead!=null;
  }

  public Object next() {
    Object v = lookahead;
    consume();
    return v;
  }

  public void remove() {
    throw new RuntimeException("unimplemented method: StripIterator remove()");
  }

  /** The result of asking for the string of an iterator is the list of elements
   *  and so this is just the list w/o nulls.  This is destructive
   *  in that the iterator cursors have moved to the end after printing.
   */
  public String toString() {
    StringBuffer buf = new StringBuffer();
    while ( this.hasNext() ) {
      buf.append(this.next());
    }
    return buf.toString();
  }
}