comparetobuilder.java

Classifier4J是一个很好的基于java的分类器,里面有Native bayes和KNN等方法的文本分类.另外还 提供了分词和自动摘要等功能

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 *    any, must include the following acknowledgement:
 *       "This product includes software developed by the
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 *    if and wherever such third-party acknowledgements normally appear.
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package net.sf.classifier4J.util;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.Comparator;

/** 
 * Assists in implementing {@link java.lang.Comparable#compareTo(Object)} methods.
 *
 * It is consistent with <code>equals(Object)</code> and
 * <code>hashcode()</code> built with {@link EqualsBuilder} and
 * {@link HashCodeBuilder}.</p>
 *
 * <p>Two Objects that compare equal using <code>equals(Object)</code> should normally
 * also compare equal using <code>compareTo(Object)</code>.</p>
 *
 * <p>All relevant fields should be included in the calculation of the
 * comparison. Derived fields may be ignored. The same fields, in the same
 * order, should be used in both <code>compareTo(Object)</code> and
 * <code>equals(Object)</code>.</p>
 *
 * <p>To use this class write code as follows:</p>
 *
 * <pre>
 * public class MyClass {
 *   String field1;
 *   int field2;
 *   boolean field3;
 *
 *   ...
 *
 *   public int compareTo(Object o) {
 *     MyClass myClass = (MyClass) o;
 *     return new CompareToBuilder()
 *       .appendSuper(super.compareTo(o)
 *       .append(this.field1, myClass.field1)
 *       .append(this.field2, myClass.field2)
 *       .append(this.field3, myClass.field3)
 *       .toComparison();
 *   }
 * }
 * </pre>
 *
 * <p>Alternatively, there is a method {@link #reflectionCompare reflectionCompare} that uses
 * reflection to determine the fields to append. Because fields can be private,
 * <code>reflectionCompare</code> uses {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} to
 * bypass normal access control checks. This will fail under a security manager,
 * unless the appropriate permissions are set up correctly. It is also
 * slower than appending explicitly.</p>
 *
 * <p>A typical implementation of <code>compareTo(Object)</code> using
 * <code>reflectionCompare</code> looks like:</p>

 * <pre>
 * public int compareTo(Object o) {
 *   return CompareToBuilder.reflectionCompare(this, o);
 * }
 * </pre>
 *
 * @see java.lang.Comparable
 * @see java.lang.Object#equals(Object)
 * @see java.lang.Object#hashCode()
 * @see EqualsBuilder
 * @see HashCodeBuilder
 * @author <a href="mailto:[e-mail]">Steve Downey</a>
 * @author Stephen Colebourne
 * @author Gary Gregory
 * @author Pete Gieser
 * @since 1.0
 * @version $Id: CompareToBuilder.java,v 1.1 2005/02/04 05:30:28 nicklothian Exp $
 */
public class CompareToBuilder {
    
    /**
     * Current state of the comparison as appended fields are checked.
     */
    private int comparison;

    /**
     * <p>Constructor for CompareToBuilder.</p>
     *
     * <p>Starts off assuming that the objects are equal. Multiple calls are 
     * then made to the various append methods, followed by a call to 
     * {@link #toComparison} to get the result.</p>
     */
    public CompareToBuilder() {
        super();
        comparison = 0;
    }

    //-----------------------------------------------------------------------
    /** 
     * <p>Compares two <code>Object</code>s via reflection.</p>
     *
     * <p>Fields can be private, thus <code>AccessibleObject.setAccessible</code>
     * is used to bypass normal access control checks. This will fail under a 
     * security manager unless the appropriate permissions are set.</p>
     *
     * <ul>
     * <li>Static fields will not be compared</li>
     * <li>Transient members will be not be compared, as they are likely derived
     *     fields</li>
     * <li>Superclass fields will be compared</li>
     * </ul>
     *
     * <p>If both <code>lhs</code> and <code>rhs</code> are <code>null</code>,
     * they are considered equal.</p>
     *
     * @param lhs  left-hand object
     * @param rhs  right-hand object
     * @return a negative integer, zero, or a positive integer as <code>lhs</code>
     *  is less than, equal to, or greater than <code>rhs</code>
     * @throws NullPointerException  if either (but not both) parameters are
     *  <code>null</code>
     * @throws ClassCastException  if <code>rhs</code> is not assignment-compatible
     *  with <code>lhs</code>
     */
    public static int reflectionCompare(Object lhs, Object rhs) {
        return reflectionCompare(lhs, rhs, false, null);
    }

    /**
     * <p>Compares two <code>Object</code>s via reflection.</p>
     *
     * <p>Fields can be private, thus <code>AccessibleObject.setAccessible</code>
     * is used to bypass normal access control checks. This will fail under a 
     * security manager unless the appropriate permissions are set.</p>
     *
     * <ul>
     * <li>Static fields will not be compared</li>
     * <li>If <code>compareTransients</code> is <code>true</code>,
     *     compares transient members.  Otherwise ignores them, as they
     *     are likely derived fields.</li>
     * <li>Superclass fields will be compared</li>
     * </ul>
     *
     * <p>If both <code>lhs</code> and <code>rhs</code> are <code>null</code>,
     * they are considered equal.</p>
     *
     * @param lhs  left-hand object
     * @param rhs  right-hand object
     * @param compareTransients  whether to compare transient fields
     * @return a negative integer, zero, or a positive integer as <code>lhs</code>
     *  is less than, equal to, or greater than <code>rhs</code>
     * @throws NullPointerException  if either <code>lhs</code> or <code>rhs</code>
     *  (but not both) is <code>null</code>
     * @throws ClassCastException  if <code>rhs</code> is not assignment-compatible
     *  with <code>lhs</code>
     */
    public static int reflectionCompare(Object lhs, Object rhs, boolean compareTransients) {
        return reflectionCompare(lhs, rhs, compareTransients, null);
    }

    /**
     * <p>Compares two <code>Object</code>s via reflection.</p>
     *
     * <p>Fields can be private, thus <code>AccessibleObject.setAccessible</code>
     * is used to bypass normal access control checks. This will fail under a 
     * security manager unless the appropriate permissions are set.</p>
     *
     * <ul>
     * <li>Static fields will not be compared</li>
     * <li>If the <code>compareTransients</code> is <code>true</code>,
     *     compares transient members.  Otherwise ignores them, as they
     *     are likely derived fields.</li>
     * <li>Compares superclass fields up to and including <code>reflectUpToClass</code>.
     *     If <code>reflectUpToClass</code> is <code>null</code>, compares all superclass fields.</li>
     * </ul>
     *
     * <p>If both <code>lhs</code> and <code>rhs</code> are <code>null</code>,
     * they are considered equal.</p>
     *
     * @param lhs  left-hand object
     * @param rhs  right-hand object
     * @param compareTransients  whether to compare transient fields
     * @param reflectUpToClass  last superclass for which fields are compared
     * @return a negative integer, zero, or a positive integer as <code>lhs</code>
     *  is less than, equal to, or greater than <code>rhs</code>
     * @throws NullPointerException  if either <code>lhs</code> or <code>rhs</code>
     *  (but not both) is <code>null</code>
     * @throws ClassCastException  if <code>rhs</code> is not assignment-compatible
     *  with <code>lhs</code>
     * @since 2.0
     */
    public static int reflectionCompare(Object lhs, Object rhs, boolean compareTransients, Class reflectUpToClass) {
        if (lhs == rhs) {
            return 0;
        }
        if (lhs == null || rhs == null) {
            throw new NullPointerException();
        }
        Class lhsClazz = lhs.getClass();
        if (!lhsClazz.isInstance(rhs)) {
            throw new ClassCastException();
        }
        CompareToBuilder compareToBuilder = new CompareToBuilder();
        reflectionAppend(lhs, rhs, lhsClazz, compareToBuilder, compareTransients);
        while (lhsClazz.getSuperclass() != null && lhsClazz != reflectUpToClass) {
            lhsClazz = lhsClazz.getSuperclass();
            reflectionAppend(lhs, rhs, lhsClazz, compareToBuilder, compareTransients);
        }
        return compareToBuilder.toComparison();
    }

    /**
     * <p>Appends to <code>builder</code> the comparison of <code>lhs</code>
     * to <code>rhs</code> using the fields defined in <code>clazz</code>.</p>
     * 
     * @param lhs  left-hand object
     * @param rhs  right-hand object
     * @param clazz  <code>Class</code> that defines fields to be compared
     * @param builder  <code>CompareToBuilder</code> to append to
     * @param useTransients  whether to compare transient fields
     */
    private static void reflectionAppend(
        Object lhs,
        Object rhs,
        Class clazz,
        CompareToBuilder builder,
        boolean useTransients) {
        
        Field[] fields = clazz.getDeclaredFields();
        AccessibleObject.setAccessible(fields, true);
        for (int i = 0; i < fields.length && builder.comparison == 0; i++) {
            Field f = fields[i];
            if ((f.getName().indexOf('$') == -1)
                && (useTransients || !Modifier.isTransient(f.getModifiers()))
                && (!Modifier.isStatic(f.getModifiers()))) {
                try {
                    builder.append(f.get(lhs), f.get(rhs));
                } catch (IllegalAccessException e) {
                    // This can't happen. Would get a Security exception instead.
                    // Throw a runtime exception in case the impossible happens.
                    throw new InternalError("Unexpected IllegalAccessException");
                }
            }
        }
    }

    //-----------------------------------------------------------------------
    /**
     * <p>Appends to the <code>builder</code> the <code>compareTo(Object)</code>
     * result of the superclass.</p>
     *
     * @param superCompareTo  result of calling <code>super.compareTo(Object)</code>
     * @return this - used to chain append calls
     * @since 2.0
     */
    public CompareToBuilder appendSuper(int superCompareTo) {
        if (comparison != 0) {
            return this;
        }
        comparison = superCompareTo;
        return this;
    }
    
    //-----------------------------------------------------------------------
    /**
     * <p>Appends to the <code>builder</code> the comparison of
     * two <code>Object</code>s.</p>
     *
     * <ol>
     * <li>Check if <code>lhs == rhs</code></li>
     * <li>Check if either <code>lhs</code> or <code>rhs</code> is <code>null</code>,
     *     a <code>null</code> object is less than a non-<code>null</code> object</li>
     * <li>Check the object contents</li>
     * </ol>
     * 
     * <p><code>lhs</code> must either be an array or implement {@link Comparable}.</p>
     *
     * @param lhs  left-hand object
     * @param rhs  right-hand object
     * @return this - used to chain append calls
     * @throws ClassCastException  if <code>rhs</code> is not assignment-compatible
     *  with <code>lhs</code>
     */
    public CompareToBuilder append(Object lhs, Object rhs) {
        return append(lhs, rhs, null);