ArrayLists

Question 1

What is a Class?

Answer 1

A blueprint of an Object that defines the data and behavior of an Object

Question 2

Give an example of a Class and Object

Answer 2

A blueprint of a house is a Class. The actual house is the Object.

Question 3

What is the Collection Class?

Answer 3

The framework that allows us to store an manipulate groups of objects.

Question 4

What is an ArrayList?

Answer 4

A Collection Class Object that allows us to use Objects in an array.

Question 5

Explain the difference between an Array and an ArrayList.

Answer 5

Arrays are:

• Fixed length
• Hold one type of data
• Are accessed by index number
• Have a predefined number of elements
• May contain primitives or Objects

ArrayLists are:

• Variable in length
• Hold more than one type of data
• Use methods to access the data
• Do not need to have predefined length/size
• Can only contain Objects. No primitives

Question 6

What is the Object Class?

Answer 6

The class that holds all other Java classes

Question 7

An ArrayList is a type of:

Answer 7

List

Question 8

A List is a type of:

Answer 8

Object

Question 9

Two ways to define an ArrayList:

Answer 9

ArrayList name = new ArrayList();
List name = new ArrayList();

Question 10

In what order are the elements of an ArrayList stored?

Answer 10

In the order that they were added

Question 11

What is an import statement?

Answer 11

Imports the predefined package and class that will be used for a type of Object

Question 12

What needs to be imported to use an ArrayList?

Answer 12

java.util.ArrayList;

Question 13

What does this code do?
ArrayList  names = new ArrayList();

Answer 13

Creates a new empty ArrayList of Strings`

Question 14

How do you add an element to an ArrayList?

Answer 14

array-list-name.add(Object);

Question 15

Why can’t you add an int, double, boolean, or float to an ArrayList?

Answer 15

ArrayLists cannot hold primitive types.

Question 16

How do you return the number of elements in an ArrayList?

Answer 16

array-list-name.size();

Question 17

How do you retrieve an element at a specified index?

Answer 17

array-list-name.get(index);

Question 18

How do you get all the elements of an ArrayList?

Answer 18

Set up a for-loop to iterate through the elements using .get();

Question 19

Do ArrayLists allow duplicate elements?

Answer 19

Yes

Question 20

How do you add elements to the middle of an ArrayList?

Answer 20

array-list-name.add(index, Object);

Question 21

If you add an element at a specified index, what happens to the other elements?

Answer 21

They get pushed down

Question 22

How do you remove elements from an ArrayList?

Answer 22

array-list-name.remove(index);

Question 23

How do you find out if an element is already in an ArrayList?

Answer 23

array-list-name.contains(Object);

Question 24

How do you get the index of the first occurrence of an Object in an ArrayList?

Answer 24

array-list-name.indexOf(Object);

Question 25

How do you get the index of the last occurrence of an Object in an ArrayList?

Answer 25

array-list-name.lastIndexOf(Object);

Question 26

How do you turn an ArrayList into an Array?

Answer 26

Datatype [ ] arrayName = array-list-name.toArray(new datatype[0]);

Question 27

How do you sort an ArrayList?

Answer 27

Collections.sort(ArrayListName);

Question 28

How do you reverse the order of an ArrayList?

Answer 28

Collections.reverse(ArrayListName);

Question 29

Describe a for-each loop.

Answer 29

• A shorthand for-loop that will iterate through the entire Array/ArrayList.
• Will go from beginning to end and cannot skip elements

Question 30

How do you define a for-each loop?

Answer 30

for(datatype elem-name : array/ArrayList-name)