Chapter 5 Cis 132

Front 1

how do increment and decrement operators work?

how is they're priority arranged?

Back 1

if i=1

--------------

i++ = 1;

i = 2

-------------

++i = 2

i = 2

-------------

- the addition takes place before the code is executed if the ++ is before the variable. it will execute after the code has executed if ++ is after i

- decrement follow the same rules. both only add or subtract 1

Front 2

show a while loop that counts to 5

Back 2

int number = 1;

while (number <= 5){

System.out.println(number);

number++

}

Front 3

what is an infinity loop?

how is it prevented

Back 3

a loop that does not have an increment or decrement to stop the loop from runing, or a loop statement with a semicolon after it instead of a brace.. or you forget braces all together

- install an increment or decrement or check your braces

Front 4

how do you use loops for input validation?

Back 4

same as an if statement. if the input is valid, it will ignore/skip/breakout of the loop

- if the input is wrong, it will restart the loop and the user needs to be prompted to enter the correct value. This will be stored as the same variable name so that the loop can check for validation

team = keyboard.nextInt();

while (team < 30){

System.out.println("get more players");

team = keyboard.nextInt();

}

Front 5

What is a "do while" loop?

Back 5

a loop that will execute its contents at least once before terminating because it checks the boolean expression at the end of the loop

do{

enter = keyboard.nextInt()

}

while (enter < 50);

Front 6

What is a for loop used for?

Does it check at the beginning of the loop or then end?

can it conduct user validation?

Back 6

- executing a specified number of times

- it checks at the beginning

- no unless the validation is a number.

Front 7

what does a for loop look like?

assume you want to count to 5 and:

number =1

Back 7

for (number = 1, number < 5, number++){

system.out.println(number);

}

Front 8

can you use user input to assign the number of times a for loop executes?

Back 8

- yes

stop = keyboard.nextInt();

for (number = 1, number < stop, number++){

system.out.println(number);

}

Front 9

can you use user input to assign the increment that the for loop counts each iteration?

Back 9

yes

stop = keyboard.nextInt();

increment = keyboard.nextInt();

for (number = 1; number < stop; increment){

system.out.println(number);

}

Front 10

can you initialize two or more variables in the for loop?

what about in the test and update sections?

Back 10

- initialize = yes, use commas to separate

- test = yes but use boolean expressions like && and || to join them

- update = yea, use commas to separate

Front 11

what an accumulator and how does it work?

Back 11

an accumulator is a number that continues to have numbers added to it as long as the loop its contained in is executing

Front 12

how do you use an accumulator in a for loop?

assume you want the total sales for the week

Whats the advantage?

whats the disadvantage?

Back 12

for (int day = 1; day < 5; day++){

double sales = keyboard.nextDoube();

double totalSales += sales;

}

total sales will be added to 5 times

- advantage is the loop will terminate as soon as the user has gone thru 5 iteratios

Front 13

how do you use an accumulator in a while loop?

assume you want a running total of points scored in a season

what is a sentinal value

Whats the advantage?

whats the disadvantage?

Back 13

int points = keyboard.nextInt();

while (points != -1){

int totalPoints += points;

}

totalPoints will be added to each time the user enters a value other than -1. once -1 is entered the loop terminates. -1 is considered a sentinal value

- advantage is you do not need to know the number of games played. Disadvantage is the user needs to know to enter -1 to terminate

Front 14

Show an example of a nested loop

assume you want to average the test scores for each student

let the user tell you how many students and the number of tests per student

Back 14

double total = 0.0

int numStud = keyboard.nextDouble();

int numTest = keyboard.nextDouble();

for (int stud = 1; stud < numStud; numStud++){

for (int test = 1; test < numTest; numTest++){

double grade = keyboard.nextDouble();

double total += grade;

}

percentage = total / numTest;

}

Front 15

How do you import the class that deals with saving files to the disc?

Back 15

import java.io.*;

this will import the entire .io package

Front 16

How do you print writing to a file?

Back 16

- you must make an object from the PrintWriter class and pass a the name of the file you want to create to the constructor. user input can be substituted with keyboard.next double()

- then call the object you created and the method println the same way you'd print to a console

- object.println("writing stuff");

Front 17

what must follow when you are finished writing to a file

What about reading a file?

Back 17

objectYouCreated.close();

this takes the information you wrote out of RAM and writes it to the disc. If this is not done it will not be able to be read in the future

ObjectYouCreated.close();

Front 18

what is a throws exception?

how is it used?

where is it used?

Back 18

I think logistically it means the main method that uses methods from the .io package can throw an exception/error and this will display it on the console. Without it, it just wont run and we wont know why

- used in the method header to "rethrow" an exception as follows

public static void main(String[] args) throws IOException{

main method starts here

}

this is also to be used on objects and other methods that call this PrintWriter method

Front 19

How do you add data to an existing file?

assume you want to add data to the file named stuff.txt

Back 19

FileWriter boobie = new FileWriter(stuff.txt, true)

pass the name of the file you want to add to, a comma and then the word true thru to the constructor. this allows you to reopen the file and add to it

Front 20

how do you save files to a specific location?

assume you want to save a file named stuff.txt

on the C drive

Back 20

FileWriter boobie = new FileWriter(C:\\stuff.txt, true)

be sure to add two \\ because a single \ is the start of an escape sequence

or...

FileWriter boobie = new FileWriter(C:/stuff.txt, true)

use a single forward slash

Front 21

how do you read data from a file?

show all steps, make up your own variable and object names

Back 21

Scanner keyboard = new Scanner(System.in);

System.out.println("enter a file name: ")

name = keyboard.nextLine()

File myFile = new File(name)

Scanner reading1 = new Scanner(myFile);

String line1 = reading.nextLine();

Front 22

What line will the nextLine() methods of the scanner class read from?

Back 22

if you have not read any lines from the file yet, .nextLine() will read the first line in the file, after that it will read each line in the file from top to bottom in succession unless you pass a number through the method which will read the line of the file that the number corresponds to

Front 23

how do you read all the lines in a file?

Back 23

use the method .hasNext() as the boolean expression in a while loop. This method returns a value true if there is more to read or a value false if there is nothing left to read

inside the loop:

String friendName = yourObjectName.nextLine();

Front 24

How can you read numbers from a file?

Back 24

yourObjectName.nextDouble();

same as your use it to take a value from the user

Front 25

how can you check whether or not a file exists?

Back 25

String nameOfFile = keyboard.nextLine()

File objectName = new File(nameOfFile);

if (!objectName.exists()){

System.out.println("That file does not exist");

System.exit(0);

}

objectName.exists() will return a true or false

Front 26

when should you use .exists() method?

Back 26

anytime you are going to write a file or add data to an existing file. This method should be used with either a loop or an if statement to protect the files and the smooth flow of the program