Questions and Exercises: Interfaces


  • At the beginning of this lesson, you learned that the core collection interfaces are organized into two distinct inheritance trees. One interface in particular is not considered to be a true Collection , and therefore sits at the top of its own tree. What is the name of this interface?

  • Each interface in the collections framework is declared with the <E> syntax, which tells you that it is generic. When you declare a Collection instance, what is the advantage of specifying the type of objects that it will contain?

  • What interface represents a collection that does not allow duplicate elements?

  • What interface forms the root of the collections hierarchy?

  • What interface represents an ordered collection that may contain duplicate elements?

  • What interface represents a collection that holds elements prior to processing?

  • What interface repesents a type that maps keys to values?

  • What interface represents a double-ended queue?

  • Name three different ways to iterate over the elements of a List .

  • True or False: Aggregate operations are mutative operations that modify the underlying collection.


  • Write a program that prints its arguments in random order. Do not make a copy of the argument array. Demonstrate how to print out the elements using both streams and the traditional enhanced for statement.

  • Take the FindDupsexample and modify it to use a SortedSet instead of a Set . Specify a Comparator so that case is ignored when sorting and identifying set elements.

  • Write a method that takes a List<String> and applies String.trim to each element.

  • Consider the four core interfaces, Set , List , Queue , and Map . For each of the following four assignments, specify which of the four core interfaces is best-suited, and explain how to use it to implement the assignment.

  • Whimsical Toys Inc (WTI) needs to record the names of all its employees. Every month, an employee will be chosen at random from these records to receive a free toy.

    • WTI has decided that each new product will be named after an employee but only first names will be used, and each name will be used only once. Prepare a list of unique first names.

    • WTI decides that it only wants to use the most popular names for its toys. Count up the number of employees who have each first name.

    • WTI acquires season tickets for the local lacrosse team, to be shared by employees. Create a waiting list for this popular sport.

Check your answers.