basicdatum.java

Standord Classifier实现了一个基于Java的最大熵分类器。用于模式识别

package edu.stanford.nlp.dbm;

import java.util.*;

/**
 * Basic implementation of Datum interface that can be constructed with a 
 * Collection of features and one more more labels. The features must be
 * specified
 * at construction, but the labels can be set and/or changed later.
 *
 * @author Joseph Smarr ([e-mail])
 */
public class BasicDatum implements Datum
{
    /** features for this Datum */
    private final Collection features;

    /** labels for this Datum. Invariant: always non-null */
    private final List labels = new ArrayList();
    
    /** 
     * Constructs a new BasicDatum with the given features and labels.
     */
    public BasicDatum(Collection features,Collection labels)
    {
        this(features);
        setLabels(labels);
    }
    
    /**
     * Constructs a new BasicDatum with the given features and label.
     */
    public BasicDatum(Collection features,Object label)
    {
        this(features);
        setLabel(label);
    }
    
    /**
     * Constructs a new BasicDatum with the given features and no labels.
     */
    public BasicDatum(Collection features) { this.features=features; }
    
    /**
     * Constructs a new BasicDatum with no features or labels.
     */
    public BasicDatum() { this(null); }
    
    /** 
     * Returns the collection that this BasicDatum was constructed with.
     */
    public Collection asFeatures() { return(features); }
    
    /** 
     * Returns the first label for this Datum, or null if none have been set.
     */
    public Object label() { return((labels.size()>0)?(Object)labels.get(0):null); }
    
    /**
     * Returns the complete List of labels for this Datum, which may be empty.
     */
    public Collection labels() { return labels; }
    
    /**
     * Removes all currently assigned Labels for this Datum then adds the
     * given Label.
     * Calling <tt>setLabel(null)</tt> effectively clears all labels.
     */
    public void setLabel(Object label)
    {
        labels.clear();
        addLabel(label);
    }
    
    /**
     * Removes all currently assigned labels for this Datum then adds all 
     * of the given Labels.
     */
    public void setLabels(Collection labels)
    {
        this.labels.clear();
        if(labels!=null) this.labels.addAll(labels);
    }
    
    /**
     * Adds the given Label to the List of labels for this Datum if it is not
     * null.
     */
    public void addLabel(Object label) { if(label!=null) labels.add(label); }
    
    /** Returns a String representation of this BasicDatum (lists features and labels). */
    public String toString() { return("BasicDatum[features="+asFeatures()+",labels="+labels()+"]"); }
    
}