1214mondaytest

Question 1

What are the three main types of loops in java

Answer 1

for loop
while loop
do while loop

Question 2

Indeterminate

Answer 2

Indeterminate loop situations are those situations where we do not know in advance how many times we may have to repeat (or iterate) the loop body code. (T!)

Question 3

Type of loop favored for indeterminate situations:

Answer 3

while or do-while

Question 4

determinate

Answer 4

loop situation we know ahead of time exactly how many iterations our loop body code has to iterate.

Question 5

Type of loop favored for determinate situations:

Answer 5

Usually we’ll use either a for loop for these situations or we’ll use a counter-controlled while loop.

Question 6

Which loop is a pre-test type of loop?

Answer 6

While loop, the loop continuation condition is check first before trying to run the loop body statements

Question 7

How do we prevent an infinite loop?

Answer 7

add some code to the loop body that will eventually cause the loop continuation condition to become false

Question 8

sentinel value

Answer 8

The sentinel value is a special input value that tests the condition within the while loop. When a sentinel value of zero is entered, the while loop continuation condition becomes false, and the loop terminates or ends.

Question 9

Which type of loop is a post-test type?

Answer 9

do-while because it runs the code first and then the LCC is checked after the body code has run.

Question 10

Difference between a while loop and a do while loop?

Answer 10

do while loop the loop body statements will always run at least once, because condition is checked after the loop body executes

Question 11

Do-while loop is often used for

Answer 11

data validation

Question 12

when is the for loop used?

Answer 12

when we know in advance how many times we want the loop to execute. commonly used for arrays

Question 13

For(expression1; expression2; expression3)

Answer 13

Expression1 declares and initializes the the loop control variable or loop counter. Some texts call this the initialization action. This part of the loop header runs just once, at the start of the loop. Expression2 is the loopcontinuation condition expression. It is re-evaluated after each iteration of the loop
Expression3 is the loopcounter adjustment expression. (Some call it the action-after-each-iteration). It is the last action done in an iteration of the body code before the loop goes back to check the LCC again.

Question 14

int count = 0; count < 5; count++) ; //semicolon here is error. What happens?

Answer 14

(Logic error)

This separates the loop header from the code in the loop body. The two parts then run independently of each other.

Question 15

How do you get out of a loop if a certain condition is met?

Answer 15

with the break statement

Question 16

What does the continue keyword do?

Answer 16

it will stop further execution of just the current iteration of a loop. (T!)

Question 17

difference between continue and break?

Answer 17

continue stops only the current iteration of the loop

break is used to break out of the loop body completely, no matter how many iterations might remain

Question 18

The for : each loop for(datatype: collection_Name)

Answer 18

Basically, it allows you to process all the data values stored in the storage structure without having to worry about how many elements there are in the structure ( this saves a few lines of code)It uses what is called an iterator (it’s like an indicator that points to each value in the data structure) to iterate through the values.It does have its usefulness, but it is actually a little less powerful than a standard for loop. In the declaration statement for(datatype: collection_Name) the datatype refers to the type of data that has been stored in the data structure that has ‘collection_Name’ as its identifier

Question 19

Reading From A File Using a Scanner Object

Answer 19

If we want the Scanner object to read a file instead of the keyboard buffer, then we create it like this: // first we create a File object that has the path name of the file File myFile = new File(“DataFile_1.txt”); // then we create the Scanner and pass it the File object Scanner fileReader = new Scanner(myFile);

Question 20

A path is:

Answer 20

A string argument that indicates the location of a folder (directory) or a file in your computer’s file system.Example: “C:\Temp2” is a path to a folder(directory) on drive ‘C’

Question 21

Absolute path

Answer 21

any path string that begins with a drive letter or root prefix is known as an ABSOLUTE path

Question 22

Relative path

Answer 22

relative to the current eclipse project directory which the java program is located
C:\MyEclipseWorkspace\FileExamplesProject\output.txt

Question 23

COMMON ERROR:

Answer 23

putting the file you want to read in your ‘src’ source folder in your Eclipse project instead of in the project folder itself.
FileNotFoundException

Question 24

File class object in Java is

Answer 24

Best described as an abstract representation of file and path names. (T)

Question 25

IMPORTANT NOTE: Creating a File object

Answer 25

DOES NOT Create a corresponding file folder on your hard drive. (T!)
We could later actually create the directories on the disk by using methods such as mkdir() and mkdirs().
We can also create an actual empty file using createNewFile() IF THE FOLDERS in the path have been have been created first.

Question 26

What are exceptions

Answer 26

objects that the Java virtual Machine creates to signal that something has gone wrong in your program. We say an exception is thrown when it is created by the JVM

Question 27

How can we prevent ArrayIndexOutOfBoundsException?

Answer 27

we can prevent this exception by using “ i < array.length ; “ for our loop continuation condition.

Question 28

Why do you get ArithmeticException

Answer 28

code tries to do a division by 0

Question 29

FileNotFoundException

Answer 29

JVM cannot find the file that you specified in your path string.

Question 30

UNCHECKED flavor:

Answer 30

the coder does not have to write any special code called exception handling code

Question 31

Examples of checked exception

Answer 31

FileNotFoundException and IOException both of which involve possible file operations.

Question 32

how do you confess

Answer 32

by using the throws keyword

Question 33

Confessing using a throws clause will let your program compile properly, but it gives no _________ if the exception is actually thrown. Your program will _____.

Answer 33

Protection

crash

Question 34

biggest benefit of the try-catch is

Answer 34

after the exception is caught by your catch block, your program keeps running! it does not crash.

Question 35

what is a path

Answer 35

a string argument that indicates the location of a folder (directory) or file in your computer’s file system
Example “C:\Temp2\notes.txt” i

Question 36

path string that begins with a drive letter or root prefix is known as an _____ path

Answer 36

absolute path (T!) C:\Temp2\notes.txt

Question 37

There is a hasNext

_____() for each primitive type EXCEPT for type char, just as there is not a _______ method in the scanner class

Answer 37

nextChar() doesn’t exist

Question 38

True or false: An array is a type of data structure constructed in memory.

Answer 38

True

Question 39

Zero-based indexing

Answer 39

first cell is always number 0

Question 40

True or false Important Point : Data types may not be mixed in the elements of an array.

Answer 40

True (T!)

Question 41

Arrays are _______ with respect to data type. This means all the data values must be of the same type

Answer 41

homogeneous

Question 42

Each element has an element index number. First element of an array is always numbered as element ____

Answer 42

0 (zero).

Question 43

ARAY INDEX OPERATOR.

Answer 43

The operator we use in creating an array is the square brackets [ ],

Question 44

How do we instantiate or build the array

Answer 44

we use the new keyword and then specify how many elements we want

Question 45

To create an array to hold ten values of type int.

Answer 45

int [] myIntArray = new int [10];

Question 46

True or false: Once created the array size is fixed, or immutables.

Answer 46

true, you cannot change the number of elements (boxes) in an array once it is created

Question 47

The last element of any array will have an index number equal to

Answer 47

the (number of elements – 1).

Question 48

Create an array of String objects to hold 25 surnames:For an array of int values typed in by user:For an array of double value test scores:For an array of Scanner objects:

Answer 48

String[ ] surNameArray = new String [25];
int [ ] userInputsArray = new int [100];
double [ ] testScoresArray = new double [350];
Scanner[ ] scannerArray= new Scanner[3];

Question 49

To enter a value in any element we use an assignment statement and specify what element gets the value.

Answer 49

myIntArray[0]= 5;

Question 50

What is the index number of the 10th element?

Answer 50

9

Question 51

offers a shortcut way to declare, create and populate an array all at once by enclosing the data values inside curly braces.

Answer 51

String [ ] monthsArray = {“Jan”,”Feb”,”Mar”,”Apr”,”May”,”Jun”,”Jul”,”Aug”,”Sep”,”Oct”, ”Nov”,”Dec”};

Question 52

True or false: An array object is the only other type of object besides a String that can be created without using the new keyword.

Answer 52

TRUE

Question 53

True or false: When an array is created, Java will automatically assign a default value to each element

Answer 53

TRUE

Question 54

Default value or each primitive type in an array of type. Int, Short, Double, float, etc) boolean, char and string

Answer 54

primitive data types: 0
boolean = false
char = unicode character ‘u0000’
string will gets NULL assignment to each element

Question 55

How do you guarentee you never have an OutOfBoundsException

Answer 55

Use the arrayName.length which holds how many elements it has
for(int count=0; count < arrayName.length; count++)

Question 56

What operator should we use with arrayName.length?

Answer 56

< always

<= will set you out of bounds

Question 57

Two tips for array processing using for loops

Answer 57

1: initialize your for loop counter to 0. so it doesn’t skip first element
2: always set the LCC to < arrayName.length in order to not get an OutOfBoundsException

Question 58

Math.random( ) returns a double value ranging from

Answer 58

0.0000 up to 0.9999999999 it does not return 1.0 (T!)

Question 59

Want math.random to return a value from 0-9? 1-10?

Answer 59

times it by 10 then truncated for 0-9

times it by 10+1 then truncate for 1-10

Question 60

To generate int values with a lower end value of “low” and an upper end value of “high”, the general formula is

Answer 60

(int)(Math.random() * (highValue – lowValue + 1) + lowValue);

Example: you need to generate random values from 5 to 15 for some game. Using the formula it would look like this: (int)(Math.random() * (15 – 5 + 1) + 5), which reduces to (int)(Math.random() * (11) + 5);