插入排序之Java实现

INSERTION-SORT(A)
    for j = 2 to A.length
        key = A[j]　　　　// 将桌面的牌拿至右手
        i = j -1　　　　　// 左手中已经排序好的牌的数量
        while i > 0 and A[i] > key　　　　// 将右手中的key牌与左手中的牌从右到左进行比较
            A[i+1] = A[i]
            i = i - 1
        A[i+1] = key　　　　// 将右手中的牌插入到左手中

import java.util.ArrayList;

/**
 * 作者原创，引用请注明出处
 * @author ChameleonChen
 */
public abstract class InsertionSort<T> {
    
    public static final int A_GREATER_THAN_B = 1;
    
    public static final int A_LESS_THAN_B = 2;
    
    public static final int A_EQUALS_B = 3;
    
    /**
     * 实现a b 两个元素的比较策略。
     * ex:
     *     int elemCompare(Integer a, Integer b) {
     *         if (a > b) return InsertionSort.A_GREATER_THAN_B;
     *         else if (a < b) return InsertionSort.A_LESS_THAN_B;
     *         else return InsertionSort.A_EQUALS_B;
     *     }
     * @param a
     * @param b
     * @return a大于b，返回InsertionSort.A_GREATER_THAN_B；a小于b，返回InsertionSort.A_LESS_THAN_B
     *         a等于b，返回InsertionSort.A_EQUALS_B.
     */
    public abstract int elemCompare(T a, T b);  

    public static final int NON_DECREASING_SORT = 1;    // 非递减排序
    
    public static final int NON_INCREASING_SORT = 2;    // 非递增排序
    
    /**
     * 对elems进行排序，改变其在内存中的值。
     * 实现算法如下：
     * INSERTION-SORT(A)
     *   for j = 2 to A.length
     *       key = A[j]
     *   
     *       i = j - 1
     *       while i > 0 and A[i] > key
     *           A[i+1] = A[i]
     *           i = i - 1
     *       A[i+1] = key
     * 
     * @param elems
     * @param sortType 排序的类型：非递减排序 InsertionSort.NON_DECREASING_SORT；
     * 非递增排序InsertionSort.NON_INCREASING_SORT
     */
    public void sort(ArrayList<T> elems, int sortType) {
        if (elems == null){
            throw new NullPointerException("the elems can not be null");
        }
        
        int expected;
        switch (sortType) {
        case NON_DECREASING_SORT:
            expected = A_GREATER_THAN_B;
            break;
        case NON_INCREASING_SORT:
            expected = A_LESS_THAN_B;
            break;
        default :
            throw new IllegalArgumentException("the sortType‘s value is illegal");
        }
        
        T temp;
        for (int j=1,i; j<elems.size(); j++) {
            temp = elems.get(j);
            
            i = j - 1;
            while (i>=0 && elemCompare(elems.get(i), temp) == expected) {
                elems.set(i+1, elems.get(i));
                i = i - 1;
            }
            elems.set(i+1, temp);
        }
    }
}