Questions and Exercises: Interfaces

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Trail: Collections
Lesson: Interfaces

## Questions and Exercises: Interfaces

### Questions

> 1. Which two of the following interfaces are at the top of the hierarchies in the Java Collections Framework?
>    - `Set`
>    - `Map`
>    - `Queue`
>    - `SortedMap`
>    - `Collection`
>    - `List`

> 2. Which of the following interfaces does not allow duplicate objects?
>    - `Queue`
>    - `Set`
>    - `List`

> 3. In order for objects in a `List` to be sorted, those objects must implement which interface and method?

> 4. True or false: The `element` method alters the contents of a `Queue`.

### Exercises

> 1. Write a method with the signature:

>    >     public Collection<String> filter(Collection<String> c)

>    that (1) traverses through the elements in `c` using an `Iterator`, (2) checks whether each element meets a certain condition (in a separate method `condition` which you do not need to define right now), and (3) if the object meets the condition, adds it to the new `Collection` to return. The method should not modify the `Collection c`. Design the method to work on any collection of `String`s. Only the `condition` method should have application-specific code; we will define this method as part of an application in the exercises for the Implementations lesson.

> 2. Write a method with the signature:

>    >     public List<Integer> reverse(List<Integer> orginalList)

>    that returns a new `List` that contains the same `Integer` objects as the `originalList` argument, but in reverse order. The method should not modify the `orginalList` object.

Check your answers.

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