Java 流 ifPresent orElse /orElseGet

Question

你好，我在这里做错了什么

我想获取基础 ID，如果它不存在，则获取保险类型.. 代码 sn-ps 粘贴在下面.. 但我在 orElse 部分遇到错误，我什至尝试过 orElseGet() ...它说“Lambda的目标类型必须是一个接口”..

String type = getFoundationId(companyInsurances).orElse(()->getInsuranceType(insurance, companyInsurances));

…

private Optional<String> getInsuranceType(Insurance insurance, List<CompanyInsurance> companyInsurances) {
    return InsurancePeriodHelper.findFirstCompanyInsuranceOfType(companyInsurances, CompanyInsuranceType.POLICY_HOLDER.getValue())
             .map(companyInsurance-> insurance.getProduct());
}

private Optional<String> getFoundationId(List<CompanyInsurance> companyInsurances) {
    return InsurancePeriodHelper.findFirstCompanyInsuranceOfType(companyInsurances, CompanyInsuranceType.FOUNDATION.getValue())
            .map(companyInsurance -> companyInsurance.getCompany().getFoundationIdentifier().toString());
}

Answer 1

使用 Java-9 及更高版本，您可以简单地将 Optionals 使用 Optional.or 链接为：

String type = getFoundationId(companyInsurances)
        .or(() -> getInsuranceType(insurance, companyInsurances))
        .orElse("defaultValue");