CMSC131 Final Exam

do-while loops

do {

} while (boolean condition);

difference between while loops + do-while loops

while loops check boolean condition, do-while loops perform the body once before checking the boolean condition

for loops

common example: we want to do something 1000 times
for (int i = 0; i < 1000; i = i + 1) {

}
**everything in the parentheses after the "for" is a boolean condition

what is the boolean condition in loops called

the loop guard

what happens if the boolean condition evaluates to false in for loops

the code jumps out of the loop, no increments occur

Gaust's Formula

1 + 2 + 3 + 4 + ... + n = [n(n+1)/2]

nested loops (options for example w printing X's or O's)

- using a "formula" to compute # of Xs or Os on current row
- maintaining variable(s) for # of Xs or Os on current row
- using a comparison to decide whether to print X or O

what are the types of programming errors

syntax, semantic/logical (bugs)

what are syntax errors

- trivial, didn't follow the rules of the language
- Eclipse will flag them w/ red marks

what are semantic/logical errors

- code compiles but doesn't work right when it's run
- debug - finding mistake + fixing it

what is a piece of advice for dealing w bugs in your code

write code incrementally and test

types of conditional statements

if, if-else

if statement

if () {

}

how do if-else statements work

they either execute one block or another (never both)

if-else statement

if () {

} else {

}

true or false: for conditional statements, braces are optional for blocks containing a single statement

true

what are the logical operators with boolean expressions

&& (and), || (or), ! (not)

what does the else correspond with when nesting if and if-else statements when there are no braces

the most recent if

statements end with

semicolons

what are identifiers

the name of something in java

what are some examples of identifiers

variable names, method names, class names, packages, interfaces, enumeration

what are the rules when creating identifiers

- can only use: A-Z, a-z, 0-9, _, $
- cannot begin w a digit
- must avoid keywords

what are keywords

words that are part of the Java language

give an example of the importance of case differentiation

Else can be an identifier, else cannot

what is style for identifiers

- lower camel case for variables, methods, and packages
- upper camel case for classes, interfaces, and enumerations

how to choose meaningful identifiers

- should be made of English word(s) describing the role of the entity
- you can abbreviate, don't make it too long

when can you use single-letter identifiers

- in for-loops (when representing index numbers)
- for coordinates with computer graphics

what is a named constant

a variable that is assigned a constant value (easy for maintenance)

what is the style for named constants

all caps, underscores between words

when should you use named constants

almost every time there is a literal in your program

why are named constants important

the value of a variable may change one day, also makes it easier for readability

what keyword should you use before a variable declaration of a named constant and what does it indicate

final - says the variable's value cannot be changed later

what are the escape sequences

\" (quotation mark), \n (new line), \t (tab), \\ (one slash)

what is the scope of local variables

block scope (code that's separated by braces)

what are examples of repeating blocks of code

while loops, do-while loops, for loops

while loops

while () {

}

What are the three logical operators?

&&, ||, !

Write "truth-tables" for && and ||.

week 3 study questions

Is the following boolean expression true or false?((3 < 5) && !(1 > 14) && (-5 < -15)) || ((6 == 6) && !(2 == 2))

false

If s1 and s2 are variables representing Strings, what Java boolean expression is equivalent to "s1 is not the same as s2"?

!s1.equals(s2)

What statement must be included at the top of a file in order to use the Scanner in the file?

import java.util.Scanner;

What does IDE stand for?

Integrated Development Environment

What IDE will we use in class this semester?

Eclipse

What does CPU stand for?

Central Processing Unit

Define the term "bit".

A "binary digit" -- either 0 or 1.

Define the term "byte".

A sequence of 8 bits (not a set/collection)

What is "hardware"? Name some examples.

Physical components of the computer. (Things you can "touch"). Examples include: CPU, RAM chips, mother board, disk drives, monitor, mouse, keyboard, cables.

What is "software"? Name some examples.

These are the "programs" or "apps" that you can run on a computer. Examples: Internet browsers, games, word processors, spreadsheet programs, the operating system, etc.

Name several different operating systems

Windows, macOS, Android, ios, unix, linux, solaris

Give some examples of secondary memory devices.

Hard drives, flash memory devices, CD's , DVD's

What is the advantage of primary memory over secondary?

It is typically much faster.

What is the advantage of secondary memory over primary?

It is permanent. (Also usually there is more of it!)

What does I/O stand for? Give some examples of I/O devices.

Input/Output. These are devices that allow you to communicate with the computer: monitor, keyboard, mouse, printer, etc.

How many different combinations of 0's and 1's can be represented using 7 bits?

2^7 = 128

How many bytes are in a kilobyte?

2^10 = 1024 (1000)

How many bytes are in a megabyte?

2^20 (1 million)

How many bytes are in a gigabyte?

2^30 (1 billion)

Name four things that the operating system does for you.

- Process management
- Memory management
- Primitive I/O
- Windowing
- Primitive network control
- Security management

What do you call the language that the CPU uses (0's and 1's represent instructions in this language)?

machine language (CPUs don't understand java)

How does "assembly language" relate to your answer to the previous question?

Assembly language is a mnemonic representation of machine language (assembly language is low-level, readable matching language)

Translate the number 123 into base 7 representation.

234 (base 7)

Translate the binary (base 2) number 1011010 into base 10 representation.

90

Translate the hexadecimal (base 16) number 7F into binary representation.

01111111

Translate the decimal (base 10) number -16 into 8 bit 2's complement representation.

11110000

what number base do we normally use for numbers

base 10 or decimal

what are important bases in CS

base 2 (binary), base 16 (hexadecimal)

how to convert from another base to base 10 (example with 1032 base 4)

starting from the right, take the digit and multiply it by the other base to the power of what position the number is in
1032 base 4:
2 x 4^0 = 2
3 x 4^1 = 12
0 x 4^2 = 0
1 x 4^3 = 64
2 + 12 + 64 = 78

digits in binary

0, 1

digits in hexadecimal

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A (10), B (11), C (12), D (13), E (14), F (15)

how to convert from base 10 to another base

divide the given number by the other base multiple times, take the remainders as digits starting from the ones place and going to the left

how to convert from base 10 to binary

write out the bits (128, 64, 32, 16...) and put 0s and 1s where necessary

converting hex to binary

for each character in hex, make a 4 digit binary equivalent and combine

converting from binary to hex

split the binary into sections of 4, add leading 0s, convert each section into the hex equivalent

what does the cpu do

process actual instructions, multiple cores like independent brains, often has 2 threads per core

what does ram stand for

random access memory (or primary memory)

what are i/o devices

input/output devices

what is an abstraction of RAM

a sequence of cells that each have an address and contain a byte of data

how many permutations of 0s and 1s can be stored in one cell

2^8 = 256

how many permutations of 0s and 1s can be represented by k bits

2^k

How many bytes are in a terabyte?

2^40 (1 trillion)

how are non-negative whole numbers stored

covert to binary, pad with leading 0s

how are negative whole numbers stored

two's complement (convert to binary, flop the digits, add 1) (more efficient)

any binary number that starts with 1 is...

negative

how are floating point numbers stored

as scientific notation (translate to binary, but into scientific notation)

how is 0 stored

as all 0s

what is the mantissa

the fractional part of a floating point number

how is text stored

old way: ascii (american standard code for information interchange), 1 byte per character

new way: unicode (more than 1 version), typically 2 bytes per character, each character is translated into code

how does java translate high level code to machine code

fast and portable: java program --> compiler ---> java bytecode program --> java interpreter for the operating systems (a combination of compiler and interpreter)

what is bytecode

close to assembly language, universal, used by java

what is a compiler

takes files and makes executable files that can be run on the CPU, runs faster, not portable, translates source code to machine code

what is an interpreter

takes source code, translates into machine code line-by-line while running, translation is completed live, takes CPU times, portable source code

what is an object

entities that interact with each other when the program is running

what is a class

a description/definition of an object (a blueprint)

what is a method

a chunk of code that has a name

what is the main method

where the program starts

what is a statement

an instruction, statements are sequential not "connected"

what are comments

not part of the program, in English to explain what's going on

multi-line comment

/* */

single line comment

//

System.out.print

prints the text