How would you write a Java Stream to fetch all employees under the age of thirty?

The question is asking you to demonstrate your ability to use Java Streams, specifically to filter out a collection of objects based on a certain property of those objects. In this case, you need to filter a collection of Employee objects to include only those whose age is less than 30. To answer this question effectively, these are the key points you should keep in mind:

• You need to know how to use the filter() function of Java Streams.
• You need to be able to write a lambda expression to apply to each object in the stream. This can be simple, in this case you want to compare the age property of each Employee object to the number 30.
• A crucial thing is how you terminate the stream operation. You have to decide whether to collect the result into a new list or process it in some other way.

Suppose we have a List of Employee objects named allEmployees. The Java Stream to fetch all employees under the age of 30 would look something like this:

List<Employee> youngEmployees = allEmployees.stream()
    .filter(e -> e.getAge() < 30)
    .collect(Collectors.toList());

In this example, we use the stream() function to convert the list to a stream, then filter() to filter the stream based on the age of each Employee, and finally collect() to convert the stream back into a list.

Another way of approaching this d could be using Java Stream to loop through employees and print details of younger employees. Here's an example:

allEmployees.stream()
    .filter(e -> e.getAge() < 30)
    .forEach(e -> System.out.println(e.getName() + " " + e.getAge()));

In this case, instead of collecting the result into a new list, we directly print the name and age of each qualified employee.