Abstract Data Types

Question 1

What is an abstract data type?

Answer 1

A definition of an organization of data and the operations we can perform on it

Question 2

What is a Stack?

Answer 2

Stack:
- the only item you can see is the one at the top of the stack
- items are added to the top (push)
- you can only remove the top item (pop)
- optionally, you can define a peek method to look at the top
item without popping it
- there should also be an isEmpty method

Question 3

What is a Queue?

Answer 3

Queue:
- add items to the end, remove items from the front
- add: Enqueue
- remove: Dequeue
- also has an optional peek method to see the top
- there should be an isEmpty method

Question 4

What is Abstraction?

Answer 4

A strategy of ignoring the details: focus on what’s important in a context and ignore the details. It allows us to build systems out of complex components without getting lost.

Question 5

What is a data abstraction?

Answer 5

A description of data storage according to the organization of the data, and the operations we can perform on it

Question 6

How can you make a collection that can hold any type of data?

Answer 6

specify its type as Object. This means you can have any type stored in the collection, but you cannot use class-specific methods or operations on them, unless you cast them first

Question 7

How can you safely cast an Object?

Answer 7

Use the instanceof operator, which gives a boolean result.

Question 8

What are some applications of stacks?

Answer 8

• to reverse items
• to return path finding
• the run-time stack
• replacing recursion: by defining our own stack, we can
  simulate the use of the run-time stack in a recursive
  function

Question 9

What are some applications of queues?

Answer 9

• when a program has to keep track of the work it needs
  to do, it can add the tasks to a queue and execute them
  in order
• as a buffer: to store a sequence of data values that need
  to be processed