com.clican.pluto.common.util.SearchUtils.java Source code

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Here is the source code for com.clican.pluto.common.util.SearchUtils.java

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/**
 * The Clican-Pluto software suit is Copyright 2009, Clican Company and individual contributors, and is licensed under the GNU LGPL.
 *
 * @author wei.zhang
 *
 */
package com.clican.pluto.common.util;

import java.util.List;

import org.apache.commons.beanutils.PropertyUtils;

public class SearchUtils {

    /**
     * ???????source???
     * 
     * @param <T>
     *            
     * @param <K>
     *            
     * @param source
     *            ?
     * @param comparablePropName
     *            ?
     * @param comp
     *            
     * @return
     */
    @SuppressWarnings("unchecked")
    public static <T, K> T binarySearch(List<T> source, String comparablePropName, Comparable<K> comp) {
        if (source == null || source.size() == 0) {
            return null;
        }
        int first = 0, upto = source.size();
        while (first < upto) {
            int midIdx = (first + upto) / 2;// Compute mid point.
            T mid = source.get(midIdx);
            try {
                K value = (K) PropertyUtils.getProperty(mid, comparablePropName);
                if (comp.compareTo(value) < 0) {
                    upto = midIdx; // repeat search in bottom half.
                } else if (comp.compareTo(value) > 0) {
                    first = midIdx + 1; // Repeat search in top half.
                } else {
                    return source.get(midIdx);// Found it. return position
                }
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
        return null; // Failed to find key
    }

    /**
     * ????
     * 
     * @param <T>
     *            
     * @param <K>
     *            
     * @param source
     *            ?
     * @param comparablePropName
     *            ?
     * @param comp
     *            
     * @return
     */
    @SuppressWarnings("unchecked")
    public static <T, K> T searchPreviousNearestInput(List<T> source, String comparablePropName,
            Comparable<K> comp) {
        if (source == null || source.size() == 0) {
            return null;
        }
        for (int i = (source.size() - 1); i >= 0; i--) {
            T input = source.get(i);
            try {
                K value = (K) PropertyUtils.getProperty(input, comparablePropName);
                if (comp.compareTo(value) >= 0) {
                    return input;
                }
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }

        return null;
    }

    /**
     * This method implements the binary search algorithm.
     * the list element and key should implement the comparable interface.
     * @param list
     *        must be sorted before, in ascendent order.
     * @param key
     *        the object that will be compared.
     * @param before
     *        if there is not a the same object, get the previous or next object
     * @return
     */
    public static <V extends Comparable<V>> V binarySearch(List<V> list, V key, boolean before) {
        if (list == null || list.size() == 0) {
            return null;
        }
        int low = 0;
        int high = list.size() - 1;

        while (low <= high) {
            int mid = (low + high) >>> 1;
            Comparable<V> midVal = list.get(mid);
            midVal.compareTo(key);
            int cmp = midVal.compareTo(key);

            if (cmp < 0)
                low = mid + 1;
            else if (cmp > 0)
                high = mid - 1;
            else
                return list.get(mid); // key found
        }
        if (before) {
            int index = high;
            if (index < 0) {
                return null;
            }
            return list.get(index);
        } else {
            int index = low;
            if (index < 0) {
                return null;
            }
            if (index >= list.size()) {
                return null;
            }
            return list.get(index);
        }

    }

}

// $Id$