edgecomparator.java

JAVA版的蚂蚁算法(Ant Colony Optimization Algorithms)

package dk.itu.nulx30.graph;

import java.util.Comparator;

/**
 * This small class makes it possible to make a comparison of
 * <code>Edge</code>-objects based on a <code>String</code>-parameter given to
 * the constructor of this class. The <code>compare()</code>-method uses the
 * method <code>getAttribute()</code> of class <code>Edge</code>.<br>
 * <br>
 * This method uses reflection to extract a field-value based on the
 * <code>String</code>-argument.
 *
 * @author  Mikkel Bundgaard
 * @author  Troels C. Damgaard
 * @author  Federico Decara
 * @author  Jacob W. Winther
 */
public class EdgeComparator implements Comparator {
  /** the field in class <code>Edge</code> to compare */
  private String compareToField;
  /** the sort order be descending if true otherwise ascending */
  private boolean sortTopFirst;
  /**
   * the value to return if the first object in the method
   * <code>compare(Object, Object)</code> is larger than the second object.
   */
  private int largerThanReturn = -1;
  /**
   * the value to return if the first object in the method
   * <code>compare(Object, Object)</code> is smaller than the second object.
   */
  private int lessThanReturn = 1;

  /**
   * Class constructor specifying the field to compare and the sort order.
   *
   * @param compareToField the field in class <code>Edge</code> to compare.
   * @param sortTopFirst if true will the sort order be descending
   *        otherwise ascending.
   */
  public EdgeComparator( String compareToField, boolean sortTopFirst ){
    this.compareToField = compareToField;
    if (!sortTopFirst) {
      largerThanReturn = 1;
      lessThanReturn = -1;
    }
  }

  /**
   * Compares its two arguments for order. Returns -1, 0, or 1 if sortTopFirst
   * is false and the first argument is less than, equal to, or greater than
   * the second. Otherwise 1, 0, or -1 is returned when the first argument is
   * less than, equal to, or greater than the second.
   *
   * @param o1 the first object to be compared.
   * @param o2 the second object to be compared.
   *
   * @return -1, 0, or 1 if sortTopFirst is false and the first argument is less
   * than, equal to, or greater than the second. Otherwise 1, 0, or -1 is
   * returned when the first argument is less than, equal to, or greater than
   * the second.
   */
  public int compare( Object o1, Object o2 ) {
    double thisVal = ( ( Edge ) o1 ).getAttribute( compareToField );
    double otherVal = ( ( Edge ) o2 ).getAttribute( compareToField );
    return ( thisVal > otherVal ? largerThanReturn :
                       ( thisVal == otherVal ? 0 : lessThanReturn ) );
  }
}