java 在访问值之前调用“Optional#isPresent()”
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/47042006/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Call "Optional#isPresent()" before accessing the value
提问by Thirukumaran
As i am getting Call "Optional#isPresent()" before accessing the value in Sonar issues for the below Code Snippet , please help me to resolve this issue.
由于我在访问以下代码片段的声纳问题中的值之前收到呼叫“Optional#isPresent()”，请帮助我解决此问题。
List <Department> deptList =new ArrayList();
List<Student> studList=new ArrayList();
Department dept= studList.stream().min(comparator.comparing(Department::getDepartmentNo)).get();
Call "Optional#isPresent()" before accessing the value.
在访问值之前调用“Optional#isPresent()”。
采纳答案by Damián Rafael Lattenero
For your code working, use at least one of the safe options from Option (ha, redundancy in words allowed here)
为了让您的代码正常工作，请至少使用 Option 中的安全选项之一（ha，此处允许冗余字词）
Department dept= studList.stream().min(comparator.comparing(Department::getDepartmentNo)).orElse(null);
Where "null" should be one value for the case of the empty list, I don't know the context, that's why I put null, please, don't use null!, select a correct value
对于空列表的情况，“null”应该是一个值，我不知道上下文，这就是我放null的原因，请不要使用null！，选择正确的值
回答by Danylo Zatorsky
Optional#get()throws an exception if there is nothing inside Optional. Sonar wants you to check the optional before getting the value like in the snippet below, but I won't recommend it as the whole idea of Optionalclass is to prevent null pointer exceptions
Optional#get()如果 Optional 中没有任何内容，则抛出异常。Sonar 希望您在获取下面代码片段中的值之前检查可选项，但我不会推荐它，因为Optional类的整个想法是防止空指针异常
Optional<Department> deptOpt= studList.stream().min(comparator.comparing(Department::getDepartmentNo));
Department department = null;
if(deptOpt.isPresent())
department = deptOpt.get();
}
A better way of doing things is the fololowing:
一个更好的做事方式是以下：
Department department = deptOpt.orElse(Department::new);
In this case, deptOpt returns a default Department object in case Optional doesn't contain any value (is empty).
在这种情况下，如果 Optional 不包含任何值（为空），则 deptOpt 将返回一个默认的 Department 对象。
Anyway - whatever approach you choose should fix your problem with Sonar.
无论如何 - 无论您选择哪种方法都可以解决声纳问题。
