Luxoft interview question

Asked about multithreading: the difference between submit and execute in the ExecutorService Lifecycle of threads Difference between Exceptions and Error Explain HashMap and its time complexity He asked to create a user class with three attributes and create six users(4 females, 2 males). After it, asked me to calculate the average age of all females After it, he asked me to create an interface with 4 methods, a, b, c and d. He asked me to change the interface in order to the method b is default and c is private static. I asked something to him about this question, and he didn't say anything. After it, he asked me if I could call this function with lambda. I said no, only if I have one method in the interface. Then, he asked me how modify this interface that it would be possible.