自己做的一种计算器算法的设计..不知道代码是否有bug

package Test;
import java.util.Scanner;
/**
 * 设计一个计算器，实现多行输入，并分别输出结果
 * 输入：
 *     4/2+5+9*7-9
 *  3*2+8/2-7+2
 *  3+8*4-5+3+1
 *  9/4/2+7-6-1
 * 输出：
 *     61
 *  5
 *  34
 * @author litaiqing
 *
 */
public class Test {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while(scanner.hasNext()){
            String in = scanner.nextLine();
            System.out.println(calc(in));
        }
    }
    public static int calc(String in){
        int result = 1;
        if(in.contains("+")){
            String[] nums = in.split("\+");
            result = calc(nums[0]);
            for(int i = 1; i < nums.length; i++){
                result += calc(nums[i]);
            }
        }else if(in.contains("-")){
            String[] nums = in.split("\-");
            result = calc(nums[0]);
            for(int i = 1; i < nums.length; i++){
                result -= calc(nums[i]);
            }
        }else if(in.contains("*")){
            String[] nums = in.split("\*");
            result = calc(nums[0]);
            for(int i = 1; i < nums.length; i++){
                result *= calc(nums[i]);
            }
        }else if(in.contains("/")){
            String[] nums = in.split("/");
            result = calc(nums[0]);
            for(int i = 1; i < nums.length; i++){
                result /= calc(nums[i]);
            }
        }else{
            result = Integer.parseInt(in);
        }
        return result;
    }
}

输出

4/2+5+9*7-9
61
3*2+8/2-7+2
5
3+8*4-5+3+1
34
9/4/2+7-6-1
1