Packages/Importing problem with FRC Java

[TeamMarcies]

So currently I am trying to use the following VALID java statement:

public Executor executor = Executors.newSingleThreadExecutor();

It requires these two imports:

import java.util.concurrent.Executor;
import java.util.concurrent.Executors;

which require this package:

package java.util.concurrent;

Which isn't found according to Netbeans but is found when I am working with a default java project.

Is this simply not allowed to be used?
I am wanting to use threads in autonomous mode and through that, use Executors that will allow threads to be placed in queue so I can have them executed in the order I have threads be executed in.

Also, are threads allowed to be used?