一、查找类

/** * 查找算法 *  * @since 2016.09.06 * */public class BinarySearch {        /**     * 递归实现二分查找，返回该数字在数组中的索引     *      * @param array 数组     * @param startIndex 开始索引     * @param endIndex 结束索引     * @param need 需要查找索引的数字     * @return need数字在数组中的位置(即索引)     */    public static int getIndexFromArray(int[] array,int startIndex,int endIndex,int need){                if(array.length <= 0 || startIndex < 0 || endIndex < 0 || endIndex <= startIndex){            return -1;        }                int middleIndex = (startIndex + endIndex) / 2;                if(middleIndex > array.length - 1){            return -1;        }                if(need == array[middleIndex]){            return middleIndex;        }                if(need > array[middleIndex]){            startIndex = middleIndex;        }else{            endIndex = middleIndex;        }                return getIndexFromArray(array, startIndex, endIndex, need);            }        /**     * 遍历查找，返回该数字在数组中的索引     *      * @param array 数组     * @param need 需要查找索引的数字     * @return need数字在数组中的位置(即索引)     */    public static int getIndexFromListArray(int[] array,int need){        if(array.length <= 0){            return -1;        }        for(int j = 0;j < array.length;j++){            if(array[j] == need){                return j;            }        }        return -1;    }}

二、测试类

public class Test {        public static void main(String[] args) {                int size = 9000000;        int[] array = new int[size];                for(int i = 0;i < size;i++){            array[i] = i + 1;        }                int need = 8999999;                long s = System.currentTimeMillis();        int index = BinarySearch.getIndexFromArray(array, 0, array.length, need);        System.out.println("二分查找耗时：" + (System.currentTimeMillis() - s));                s = System.currentTimeMillis();        int indexRepeat = BinarySearch.getIndexFromListArray(array, need);        System.out.println("遍历查找耗时：" + (System.currentTimeMillis() - s));                System.out.println(index + " || " + indexRepeat);            }} 执行结果： 二分查找耗时：0 遍历查找耗时：5 8999998 || 8999998