package edu.stanford.nlp.util;import java.util.*;/** * Index is a list which maps between an Object vocabulary and * contiguous integer indices.  It supports constant-time lookup in * both directions.   * <p> * The typical usage would be: * <p><code>Index index = new Index(collection);</code> * <p> followed by * <p><code>int i = index.indexOf(object);</code> * <p> or * <p><code>Object o = index.get(i);</code> * The source contains a concrete example of use. * * @author <a href="mailto:klein@cs.stanford.edu">Dan Klein</a> * @version 1.0 * @since 1.0 * @see AbstractList */public class Index extends AbstractList {  protected List objects = new ArrayList();  protected Map indexes = new HashMap();  protected boolean locked = false;  /** Returns the index of each elem in an array. */  public int[] indices(List elems)  {      int[] indices=new int[elems.size()];      for(int i=0;i<elems.size();i++)          indices[i]=indexOf(elems.get(i));      return(indices);  }    public int size() {    return objects.size();  }  public Object get(int i) {    return objects.get(i);  }  public boolean isLocked() { return locked; }  public void lock() { locked = true; }  public void unlock() { locked = false; }  public int indexOf(Object o) {    Integer index = (Integer)indexes.get(o);    if (index == null)      return -1;    return index.intValue();  }  public int lastIndexOf(Object o) {    return indexOf(o);  }  public boolean addAll(Collection c) {    boolean changed = false;    for (Iterator cI = c.iterator(); cI.hasNext();) {      changed &= add(cI.next());    }    return changed;  }  public List subList(int from, int to) {    throw new UnsupportedOperationException();  }  public boolean add(Object o) {    Integer index = (Integer)indexes.get(o);    if (index == null && ! locked) {      index = new Integer(objects.size());      objects.add(o);      indexes.put(o, index);      modCount++;      return true;    }    return false;  }  public boolean contains(Object o) {    return indexes.containsKey(o);  }  public Index() {    super();  }  public Index(Collection c) {    super();    addAll(c);  }  public static void main(String[] args) {    List list = new ArrayList();    list.add("A");    list.add("B");    list.add("A");    list.add("C");    Index index = new Index(list);    System.out.println("Index size: "+index.size());    System.out.println("Index has A? : "+index.contains("A"));    System.out.println("Index of A: "+index.indexOf("A"));    System.out.println("Index of B: "+index.indexOf("B"));    System.out.println("Index of C: "+index.indexOf("C"));    System.out.println("Object 0: "+index.get(0));      }}