为什么我在这个Java代码中收到“死代码”警告？

Question

Would someone please tell me why i am getting a dead code warning in the else branch of if (projectId != null) ? If i got this right, the interpreter thinks projectId can never be null - is that right? In my opinion this is not possible...

Integer projectId = null;

if (!sprintTaskConnections.isEmpty())
    projectId = sprintTaskConnections.get(0).getProjectId();

// init name, state, startDate, endDate here

JiraSprint sprint = new JiraSprint(sprintInfo.getInt("id"), name, state, projectId, startDate, endDate);

if (projectId != null)
{
   ...
}

Even if i put a

sprintTaskConnections.add(new JiraSprintTaskConnection(1, 1, 1));

or a

sprintTaskConnections.clear();

in front of

if (!sprintTaskConnections.isEmpty())
projectId = sprintTaskConnections.get(0).getProjectId();

the result is always the same!

Please help me, i just don't get it at the moment!

Answer 1

I don't have the JiraSprint code, so I can't confirm this, but I suspect the JiraSprint constructor takes an int where you pass in the projectId rather than an Integer . That forces Java to auto-unbox the Integer. If the Integer projectId is null, you'll get a NullPointerException (because of the auto-unboxing) there, so you won't even get to the if block. Therefore, projectId must not be null.

Answer 2

Maybe: new JiraSprint(..) gets int projectId ?

In that case, if projectId is null , this line:

JiraSprint sprint = new JiraSprint(sprintInfo.getInt("id"), name, state, projectId, startDate, endDate);

will throw NPE, so projectId cannot be null after this line.

Answer 3

projectId很有可能永远为null，因此“if”中的代码永远不会被执行