Example 8.30 Implementing Generic ValueListHandler Class

package corepatterns.apps.psa.util;

import java.util.*;

public class ValueListHandler
implements ValueListIterator {

  protected List list;
  protected ListIterator listIterator;

  public ValueListHandler() {
  }

  protected void setList(List list) 
  throws IteratorException {
    this.list = list;
    if(list != null)
      listIterator =  list.listIterator();
    else
      throw new IteratorException("List empty");
  }

  public Collection getList(){
    return list;
  }
    
  public int getSize() throws IteratorException{
    int size = 0;
        
    if (list != null)
      size = list.size();
    else
      throw new IteratorException(...); //No Data

    return size;
  }
    
  public Object getCurrentElement() 
  throws IteratorException {

    Object obj = null;
    // Will not advance iterator
    if (list != null)
    {
      int currIndex = listIterator.nextIndex();
      obj = list.get(currIndex);
    }
    else
      throw new IteratorException(...);
    return obj;

  }
    
  public List getPreviousElements(int count) 
  throws IteratorException {
    int i = 0;
    Object object = null;
    LinkedList list = new LinkedList();
    if (listIterator != null) {
      while (listIterator.hasPrevious() && (i < count)){
        object = listIterator.previous();
        list.add(object);
        i++;
      }
    }// end if
    else
      throw new IteratorException(...); // No data

    return list;
  }
    
  public List getNextElements(int count) 
  throws IteratorException {
    int i = 0;
    Object object = null;
    LinkedList list = new LinkedList();
    if(listIterator != null){
      while(  listIterator.hasNext() && (i < count) ){
        object = listIterator.next();
        list.add(object);
        i++;
      }
    } /  / end if
    else
      throw new IteratorException(...); // No data

    return list;
  }
    
  public void resetIndex() throws IteratorException{
    if(listIterator != null){
      listIterator = list.ListIterator();
    }
    else
      throw new IteratorException(...); // No data
  }
  ...
}