如果找到，可以使用字符串替换将+91替换为空白

String countrycode = +91;

String mobileNumber = 123917890;

String noCountryCode = mobileNumber.replace("+91", "");

System.out.println(noCountryCode);

你得打电话 .substring 在 mobileNumber 而不是开着 num_code .
演示：

class Main {
    public static void main(String[] args) {
        String countrycode = "+91";

        // Test numbers
        String[] mobileNumbers = { "+91123917890", "123917890" };

        for (String mobileNumber : mobileNumbers) {
            if (mobileNumber.contains(countrycode)) {
                int v = countrycode.length();
                String phonenumber = mobileNumber.substring(v);
                System.out.println(phonenumber);
            } else {
                System.out.println("mobile number doesn't have country code");
            }
        }
    }
}

输出：

123917890
mobile number doesn't have country code

我得到了答案，谢谢大家对我的帮助
很简单

String countrycode = +91;

String mobileNumber = 123917890;

if (mobileNumber.contains("+" + countrycode)){
                    int v = countrycode.length();
                    String phonenumber = num_code.substring(v);
                    System.out.println(phonenumber);
                } else {
                    System.out.println("mobile number doesn't have country code");
                }

现在它正在按预期的结果工作。