Arrays and Arraylists

Question 1

What is the major difference between arrays and ArrayLists?

Answer 1

ArrayLists are dynamic and we do not have to specify the size while creating it. Arrays are created with a set immutable size.

Question 2

What Java package is the ArrayList a part of?

Answer 2

java.util

Question 3

What is the syntax to import an ArrayList?

Answer 3

import jave.util.ArrayList;

Question 4

What is the syntax to create an array of double of the size 5 named score?

Answer 4

double[] score = new double[5];

Question 5

What is the syntax to create an array of Strings named flavor with the data “Chocolate”, “Strawberry”, “Vanilla”?

Answer 5

String[] flavor = {“Chocolate”, “Strawberry”, “Vanilla”};

Question 6

What is the syntax to create an ArrayList of data type Double of the size 5 named score?

Answer 6

ArrayList<Double> score = new ArrayList<>(5);
Note that the initial capacity is optional, but it can improve performance if you know the size of the ArrayList in advance.</Double>

Question 7

What is the syntax to create an ArrayList of Strings named flavor with the data “Chocolate”, “Strawberry”, “Vanilla”?

Answer 7

ArrayList<String> flavor = new ArrayList<>();
flavor.add("Chocolate");
flavor.add("Strawberry");
flavor.add("Vanilla");</String>

Question 8

What is the syntax to print out the values of a one dimensional array named flavor to the output console?

Answer 8

This will print the array like [xxx,xxx,xxx]
System.out.println(Arrays.toString(flavor));

These next two will print out each array item on it’s own line:
Arrays.stream(flavors).forEach(System.out::println);

for (String favor : flavors) {
System.out.println(flavor);
}

Question 9

What is the syntax to print out the values of an ArrayList named flavor to the output console?

Answer 9

This will print the ArrayListlike [xxx,xxx,xxx]
System.out.println(Arrays.toString(flavor));

These next two will print out each ArrayList item on it’s own line:
for(String f : flavor) {
System.out.println(f);
}
Or
flavor.forEach(System.out::println);

Question 10

What is the syntax to print out the values of a two dimensional array named flavor to the output console?

Answer 10

This will print out [[xxx,xxx],[xxx,xxx],[xxx,xxx]]
(notice the strings aren’t enclosed in “”)
System.out.println(Arrays.deepToString(flavor));

Question 11

What is the syntax to remove the 3rd element in an ArrayList named flavor?

Answer 11

flavor.remove(3);

Question 12

What is the syntax to add “Peppermint” to the end of an ArrayList named flavor?

Answer 12

flavor.add(“Peppermint”);

Question 13

Can an ArrayList use primative data types?

Answer 13

No. We need to use the corresponding wrapper classes.

Question 14

What is the class we need to import in order to declare a ArrayList with an array and what is the import syntax?

Answer 14

import java.util.Arrays;

Question 15

What is the syntax to create an ArrayList of Strings named flavor with the data “Chocolate”, “Strawberry”, “Vanilla” using an ArrayList constructor? Include the import statements.

Answer 15

import java.util.ArrayList;
import java.util.Arrays;
ArrayList<String> flavor = new ArrayList<>(
Arrays.asList("Chocolate", "Strawberry", "Vanilla")
);</String>

Question 16

What is the syntax to find the length of an array named footballScores and save the value into a int variable named numberOfScores?

Answer 16

numberOfScores = footballScores.length;

Question 17

What is the syntax to find the length of an array named footballScores and save the value into a int variable named numberOfScores?

Answer 17

numberOfScores = footballScores.length;

Question 18

What is the syntax to add “Cotton Candy” to a ArrayList named flavor?

Answer 18

flavor.add(“Cotton Candy”);

Question 19

What is the syntax to add “Cotton Candy” between “Chocolate” and “Strawberry” in a ArrayList named flavor with the data “Chocolate”, “Strawberry”, “Vanilla”?

Answer 19

flavor.add(1, “Cotton Candy”);

Question 20

What is the syntax for the two ways of removing “Cotton Candy” in a ArrayList named flavor with the data “Chocolate”, “Cotton Candy”, “Strawberry”, “Vanilla”?

Answer 20

flavor.remove(1);
When an int data type is passed into .remove the element at that index will be removed.
flavor.remove(“Cotton Candy”);
When a data type that is the same as the data type that is being stored by the ArrayList, is passed into .remove the first instance of that value found will be removed.

Question 21

When using .remove on an ArrayList with the data type int will java use the index or the value to find the element to be removed?

Answer 21

Since java will not know whether you mean the index or the value it will default to using the index.

Question 22

What is the syntax to print the item at index 2 in the array flavor with the data “Chocolate”, “Cotton Candy”, “Strawberry”, “Vanilla”? What will be printed out?

Answer 22

System.out.println(flavor[2]);
Strawberry

Question 23

What is the syntax to print the item at index 2 in the ArrayList flavor with the data “Chocolate”, “Cotton Candy”, “Strawberry”, “Vanilla”? What will be printed out?

Answer 23

System.out.println(flavor.get(2));
Strawberry

Question 24

What is the syntax to change “Strawberry” to “Blueberry” in the array flavor with the data “Chocolate”, “Cotton Candy”, “Strawberry”, “Vanilla” and print out the new result?

Answer 24

flavor[2] = “Blueberry”;
System.out.print(Arrays.toString(flavor));

Question 25

What is the syntax to change “Strawberry” to “Blueberry” in the ArrayList flavor with the data “Chocolate”, “Cotton Candy”, “Strawberry”, “Vanilla”

Answer 25

These will make the item change:
flavor.set(2, “Blueberry”);
or if we don’t know the index of the item we want to change:
int index = flavor.indexOf(“Strawberry”);
flavor.set(index, “Blueberry”);

Question 26

What happens when trying to print out an Array list with custom objects?

Answer 26

The output will be a list of memory addresses unless we use the special method named toString

Question 27

What is the difference between .length and .length()?

Answer 27

.length is for arrays
.length() is for strings
Neither can be used on the other.

Question 28

What does Arrays.asList do?

Answer 28

It allows us to insert a list into an ArrayList when creating it.
ArrayList<Strings> names = new ArrayList<>(Arrays.asList(“Tim”, “Steve”, “Sue”);</Strings>

Question 29

How do we find the index of the item “banana” in the ArrayList fruit?

Answer 29

fruit.indexOf(“banana”);

Question 30

What is the syntax to create a two dimensional array named fruitFlavors with these items:
“Apple”, “Banana”
“Cherry”, “Grape”
“Kiwi”, “Mango”
“Orange”, “Pineapple”

Answer 30

String[][] fruitFlavors = {
{“Apple”, “Banana”},
{“Cherry”, “Grape”},
{“Kiwi”, “Mango”},
{“Orange”, “Pineapple”}
};

Question 31

What is the syntax to access and print out “Banana” from this array:
fruitFlavors = {
{“Apple”, “Banana”},
{“Cherry”, “Grape”},
{“Kiwi”, “Mango”},
{“Orange”, “Pineapple”}
};

Answer 31

System.out.println(fruitFlavors[0][1]);

Question 32

what does .indexOf return if the item searched for isn’t in the array /ArrayList searched?

Answer 32

The indexOf() method returns -1 if the item is not found in the array/ArrayList.

Question 33

If you try to print an ArrayList of custom data type elements what will you get?

Answer 33

If you try to print an ArrayList of custom data type element, you will see a list of memory addresses.