java二分查找法：

public class Test7 {
    public static void main(String[] args) {
        int [] arry = {1,3,4,7,12,24,57}; //适用于有一定的排列循序
        int findNum = 12;  //假设要查找的数
        //left和right就是要查找的范围
        int left = 0;
        int right = arry.length-1;
        int mid = arry.length/2; //查找范围的中间索引
        int index = -1;
        while (left<=right){
            if (findNum==arry[mid]){
                index = mid;
                break;
            }else if (findNum>arry[mid]){
                left=mid+1;
            }else if (findNum<arry[mid]){
                right=mid-1;
            }
            mid=(left+right)/2;
        }
        System.out.println(index);
    }
}