Lucene example source code file (Explanation.java)

This example Lucene source code file (Explanation.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lucene tags/keywords

arraylist, arraylist, explanation, explanation, idfexplanation, io, override, serializable, string, string, stringbuilder, stringbuilder, util

The Lucene Explanation.java source code

package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.Serializable;
import java.util.ArrayList;

/** Expert: Describes the score computation for document and query. */
public class Explanation implements java.io.Serializable {
  private float value;                            // the value of this node
  private String description;                     // what it represents
  private ArrayList<Explanation> details;                      // sub-explanations

  public Explanation() {}

  public Explanation(float value, String description) {
    this.value = value;
    this.description = description;
  }

  /**
   * Indicates whether or not this Explanation models a good match.
   *
   * <p>
   * By default, an Explanation represents a "match" if the value is positive.
   * </p>
   * @see #getValue
   */
  public boolean isMatch() {
    return (0.0f < getValue());
  }


  
  /** The value assigned to this explanation node. */
  public float getValue() { return value; }
  /** Sets the value assigned to this explanation node. */
  public void setValue(float value) { this.value = value; }

  /** A description of this explanation node. */
  public String getDescription() { return description; }
  /** Sets the description of this explanation node. */
  public void setDescription(String description) {
    this.description = description;
  }

  /**
   * A short one line summary which should contain all high level
   * information about this Explanation, without the "Details"
   */
  protected String getSummary() {
    return getValue() + " = " + getDescription();
  }
  
  /** The sub-nodes of this explanation node. */
  public Explanation[] getDetails() {
    if (details == null)
      return null;
    return details.toArray(new Explanation[0]);
  }

  /** Adds a sub-node to this explanation node. */
  public void addDetail(Explanation detail) {
    if (details == null)
      details = new ArrayList<Explanation>();
    details.add(detail);
  }

  /** Render an explanation as text. */
  @Override
  public String toString() {
    return toString(0);
  }
  protected String toString(int depth) {
    StringBuilder buffer = new StringBuilder();
    for (int i = 0; i < depth; i++) {
      buffer.append("  ");
    }
    buffer.append(getSummary());
    buffer.append("\n");

    Explanation[] details = getDetails();
    if (details != null) {
      for (int i = 0 ; i < details.length; i++) {
        buffer.append(details[i].toString(depth+1));
      }
    }

    return buffer.toString();
  }


  /** Render an explanation as HTML. */
  public String toHtml() {
    StringBuilder buffer = new StringBuilder();
    buffer.append("<ul>\n");

    buffer.append("<li>");
    buffer.append(getSummary());
    buffer.append("<br />\n");

    Explanation[] details = getDetails();
    if (details != null) {
      for (int i = 0 ; i < details.length; i++) {
        buffer.append(details[i].toHtml());
      }
    }

    buffer.append("</li>\n");
    buffer.append("</ul>\n");

    return buffer.toString();
  }
  
  /**
   * Small Util class used to pass both an idf factor as well as an
   * explanation for that factor.
   * 
   * This class will likely be held on a {@link Weight}, so be aware 
   * before storing any large or un-serializable fields.
   *
   */
  public static abstract class IDFExplanation implements Serializable {
    /**
     * @return the idf factor
     */
    public abstract float getIdf();
    /**
     * This should be calculated lazily if possible.
     * 
     * @return the explanation for the idf factor.
     */
    public abstract String explain();
  }
}