Unit 7 - ArrayList

Question 1

ArrayList object

Answer 1

Mutable and contains object references
Dynamic in size
Resizable length
Not designed to store primitives
Slightly slower

Question 2

ArrayList can only be used when

Answer 2

imported

Question 3

ArrayList class is implemented using

Answer 3

Arrays

Question 4

framework

Answer 4

prewritten, high-performing and efficient code that can handle and use objects of groups of data

Question 5

import statement

Answer 5

import.java.util.ArrayList

Question 6

Declaring a variable to reference an ArrayList object

Answer 6

ArrayList variableName;

Question 7

Instantiate an ArrayList object

Answer 7

Stores only elements of the same, non-primitive DataType

new ArrayList  ();
OR
new ArrayList  (n);
n= initial # of elements

Question 8

DataType must equal

Answer 8

any non-primitive data type

Question 9

Although ArrayList objects are designed to store references to objects, using

Answer 9

Wrapper class allows primitive values to be stored in ArrayList

Question 10

What ArrayList method returns the number of element in the list?

Answer 10

int size ( )

Question 11

What ArrayList method appends obj to end of list and returns true?

Answer 11

boolean (E obj)

ducks. add(Duck1);
* adding Duck1 to the end of an array named ducks

Question 12

What ArrayList method inserts obj at position index, moving elements at position index and higher to the right and adds 1 to the list size?

Answer 12

void add (int index, E obj)

symbols. add(3, flowers)
* adding “flowers” to index 3 of an array named symbols, moving all original items at 3 or above 1 index higher and adding 1 to ArrayList

Question 13

What ArrayList method removes element from position index, moving elements at position index and higher to the left and subtracts 1 to the list size while returning the elements formerly stored at position index?

Answer 13

E remove (int index)

Star s1 = stars. remove(2);
*removing element at index 2 in an array named stars & storing it as s1

System.out.print(s1);
*former element will be printed

Question 14

What ArrayList method replaces element at position index with obj and returns element formerly at position index?

Answer 14

E set (int index, E obj)

Stars s1 = stars.set(1, green star)
*setting element at index 1 in an array named stars & storing it as s1

System.out.print(s1);
*former element will be printed

Question 15

What ArrayList method returns element at position index in list?

Answer 15

E get (int index)

Star s2 = stars.get(0);

Question 16

ArrayList is preferred over ArrayList because

Answer 16

It allows compiler to find errors that would otherwise be found at run-time

Question 17

Java allows the generic ArrayList when the generic type E

Answer 17

specifies the type of elements

Question 18

When ArrayList is specified,

Answer 18

types of references parameters and return type when using the methods are type E

Question 19

When passed as a parameter in a method, ArrayList are passed as

Answer 19

References to address and not copies of their values

Question 20

When a method updates elements of a passed ArrayList, the ArrayList’s elements are

Answer 20

Updated automatically

Question 21

If a method with an ArrayList as a parameter only involves accessing elements of ArrayList without assigning or updating the elements from the ArrayList, then

Answer 21

the myMethod method signature is sufficient

myMethod(questions);

connects to method used with array name inside parentheses

Question 22

If the method involves adding, updating, or storing elements of the passed ArrayList, then

Answer 22

you need to specify the data type of elements stored in ArrayList

myMethod1(questions);
*call to method

public static void myMethod1(ArrayList arr) {}
*method being called

Question 23

In order to return an ArrayList, it is preferred that you

Answer 23

specify the type of data of elements that the ArrayList stores

Question 24

Algorithm for summing all elements in an ArrayList

Answer 24

1 - create an int sum and set to 0
2 - length of element at index i will be added to sum
3 - loop will repeat until all elements has been traversed
4- display sum

Question 25

Algorithm for removing elements in an ArrayList

Answer 25

Needs to start on the right end of an ArrayList and move down in order to captures all specified element

Question 26

Structure of enhanced for loop for ArrayList

Answer 26

for (DataType item: nameOfArrayList)
{
      //statement one
      //statement two
      // ...
}

Question 27

In enhanced for loops with ArrayList,

Answer 27

No index is needed so no set() or get()

Enhanced for loops make a copy of each entry

Question 28

During the iterations of an enhanced for loop, ArrayList elements

Answer 28

Can’t be modified, remove from, or added to ArrayList

Question 29

Common Mistakes with ArrayList

Answer 29

1- Forgetting to include import statement
2- Declaring or instantiating an ArrayList with primitive data type
ArrayList myList = new ArrayList ();
3- Forgetting to include the () at end of the ArrayList constructor call
ArrayList myList = new ArrayList ;
4- Not specifying the element type that the ArrayList references
ArrayList myList = new ArrayList();
5- Trying to update ArrayList values while using an enhanced for loop
6- Changing size of an ArrayList while traversing with an enhanced for loop
7- Removing an element from an ArrayList at the wrong time

Question 30

Searching

Answer 30

Process incorporates iteration and selection
Specify each element, one at a time, and do not need to track index after execution
Compare value retrieved with value being searched for

Question 31

Linear search algorithms

Answer 31

Best used when we don’t know any idea about order of data

Look at each element to determine if what we are looking for is in fact inside the array/ ArrayList

Question 32

Different data types requires

Answer 32

Different comparisons
int values -> == operator
double values -> close enough(math)
object instance -> .equals(otherThing)

Question 33

Selection sort

Answer 33

Identifies either max/min of compared values and iterates over structure checking if item store matches condition
If so, replaces value stored with that value
Implementation requires helper method to perform swap operation

Question 34

Insertion sort

Answer 34

Building a sorted structure as it proceed

Inserts each value it finds at appropriate location in data structure using a while loop as inner loop

Question 35

Efficiency

Answer 35

One of main way to compare programs

How many times does a particular statement get executed?

Question 36

When collecting data about users, try to

Answer 36

Remove data collected
Minimize data collection
Anonymizing personal data