Cis 260 Chapter 2

Front 1

algorithm

Back 1

describes how a problem is solved in terms of the actions to be executed and the order of their execution

help the programmer plan a program before writing it in a programming language

described in natural languages or in pseudocode

Front 2

pseudocode

Back 2

natural languages mixed with programming code

Front 3

variable

Back 3

designates a location in memory for storing data and computational results in the program

has a name that can be used to access the memory location

every variable has a name, a type, a size, and a value

Front 4

descriptive names

Back 4

rather than 'x' and 'y' -->
use 'radius' for radius and 'area' for area

to let the compiler know what 'radius' and 'area' are, specify their data types

Front 5

floating-point number

Back 5

numbers with a decimal point

Front 6

primitive data types

(fundamental types)

Back 6

simple data types provided by Java for representing integers, floating-point numbers, characters, and Boolean types

Front 7

double

Back 7

indicates that the variable is a double-precision floating-point value stored in the computer

Front 8

System.out.println

Back 8

the method to display the final product in the console

Front 9

variable declarations

declaring variables

Back 9

tells the compiler to allocate appropriate memory space for the variable based on its data type

the syntax for declaring a variable is -->
datatype variableName;

a variable MUSt be declared before can be assigned a value. A variable declared in a method MUST be assigned a value before it can be used.

examples:

double radius; // Declare radius
double area; // Declare area

Whenever possible, declare a variable and assign its initial value in one step. This will make the program easy to read and avoid programming errors.

Front 10

variable declaration:

int count;

Back 10

// Declare count to be an integer variable;

Front 11

variable declaration:

double radius;

Back 11

// Declare radius to be a double variable;

Front 12

variable declaration:

double interestRate;

Back 12

// Declare interestRate to be a double variable;

Front 13

declaring variables of the same type

Back 13

if variables are of the same type, they can be declared together, as follows:

datatype variable1, variable2, ..., variablen;

the variables are separated by commas. for example,

int i, j, k; // Declare i, j, and k as int varaibles

Front 14

assign value

Back 14

the value of a variable is not defined until you assign a value

example:

radius = 20; // New value is radius

area = radius * radius * 3.141592;

Front 15

concatenating strings

Back 15

Done so with signs (+)

Front 16

string concatenation operator

Back 16

combines two strings if two operands are strings

if one of the operands is a nonstring (e.d., a number), the nonstring value is converted into a string and concatenated with the other string

Front 17

breaking a long string

Back 17

A string constants cannot cross lines in the source code. Thus the following statement would result in a compile error.

System.out.println ("Introduction to Java Programming,
by Y. Daniel Liang");

To fix the error, break the string into separate substrings, and use the concatenation operator (=) to combine them:

System.out.println("Introduciton to Java Programming, " +
"by Y Daniel Liang");

Front 18

incremental development and testing

Back 18

It is a good approach to develop and test steps incrementally by adding them one at a time

Front 19

System.out

Back 19

default - the output device is the display monitor

Front 20

System.in

Back 20

default - the input device is the keyboard

Front 21

println

Back 21

the method to display a primitive value or a string to the console

Front 22

new Scanner(System.in)

Back 22

creates an object of the Scanner type

console input is not directly supported in Java, but you can use the Scanner class to create an object to read input from System.in with -->

Scanner input = new Scanner(System.in);

Front 23

Scanner input = newScanner(System.in)

Back 23

creates a 'Scanner' object and assigns its reference to the variable 'input'

Front 24

invoke method on an object

Back 24

to perform a task

Front 25

Method:

nextByte()

Back 25

Description:

reads an integer of the 'byte' type

Front 26

Method:

nextShort()

Back 26

Description:

reads an integer of the 'short' type

Front 27

Method:

nextInt=()

Back 27

Description:

reads an integer of the 'int' type

Front 28

Method:

nextLong()

Back 28

Description:

reads an integer of the 'long' type

Front 29

Method:

nextFloat()

Back 29

Description:

reads a number of the 'float' type

Front 30

Method:

nextDouble()

Back 30

Description:

reads a number of the 'double' type

Front 31

Method:

next()

Back 31

Description:

reads a string that ends before a whitespace charachter

Front 32

Method:

nextLine()

Back 32

Description:

reads a line of text (i.e., a string ending with the 'Enter' key pressed)

Front 33

nextDouble()

Back 33

for now, we'll see how to read a number that includes a decimal point by invoking the nextDouble() method

Front 34

import class

Back 34

import java.util.Scanner; // Scanner is in the java.util package

Front 35

create a Scanner

Back 35

Scanner input = new Scanner(System.in);

Front 36

read a double

Back 36

double radius = input.nextDouble()

Front 37

print vs. println

Back 37

the 'print' method is identical to the 'println' method except that 'println' moves the cursor to the next line after displaying the string, but 'print' does not advance the cursor to the next line when completed

Front 38

identifiers

Back 38

the names of things that appear in the program

identifiers are for naming variables, constants, methods, classes, and packages

descriptive identifiers make program easy to read

ex: 'ComputeAverage', 'main', 'input', 'number1', 'number2', 'number3'

Front 39

identifier naming rules

Back 39

An identifier is a sequence of characters that consists of letters, digits, underscores, and dollar signs

An identifier must start with a letter, an underscore, or a dollar sign. It cannot start with a digit.

An identifier cannot be a reserved word.

An identifier cannot be 'true', 'false', or 'null.'

An identifier can be of any length.

Front 40

illegal identifiers

Back 40

the Java compiler detects illegal identifiers (those that brea the identifier naming rules) and reports syntax errors

Front 41

naming variables

Back 41

By convention, variables are in lowercase. If a name consists of several words, concatenate all of them and capitalize the first letter of each word except the first. Examples of variables are 'radius' and 'interestRate.'

Front 42

initializing variables

Back 42

Variables often have initial values. You can declare a variable AND initialize it in one step.

int count = 1;

this is equivalent to the next two statements:

int count;
x = 1;

You can also use a shorthand form to declare AND initialize variables of the same type together. For example,

int i = 1, j = 2

Front 43

assignment statement

Back 43

after a variable is declared, you can assign a value to it by using an assignment statement

The syntax for assignment statements is as follows:

variable = expression;

Front 44

assignment operator

Back 44

In Java, the equal sign (=) is used as the assignment operator.

Front 45

expression

Back 45

represents a computation involving values, variables, and operators that, taking them together, evaluates to a value

Front 46

variables in expressions

Back 46

A variable can be used in an expression. For example,

x = x + 1;

In this assignment statement, the result of x + 1 is assigned to x. If x is 1 before the statement is executed, then it becomes 2 after the statement is executed.

To assign a value to a variable, the variable name must be on the left of the assignment operator. Thus, 1 = x would be wrong.

Front 47

assignment expression

Back 47

an assignment statement is known as an assignment expression

in Java, an assignment statement is essentially an expression that evaluates to the value to be assigned to the variable on the left-hand side of the assignment operator

System.out.println(x=1);

is equivalent to

x = 1;
System.out.println(x);

Front 48

named contant

constant

Back 48

represents permanent data that never changes

Front 49

syntax for declaring a constant

Back 49

final datatype CONSTANTNAME = VALUE;

a constant must be declared AND initialized in the same statement

Front 50

final

Back 50

a Java keyword for declaring a constant

final double PI = 3.141592; // Declare a constant

constants are named in uppercase: PI, not pi or Pi

Front 51

benefits of constants

Back 51

1) you don't have to repeatedly type the same value

2.) if you have to change the constant value (e.g.k from 3.14 to 3.141592 for PI), you need to change it only in a single location in the source code

3.) a descriptive name for constants makes the program easy to read

Front 52

the six numeric data types

Back 52

byte
short
int
long
float
double

Front 53

the four integer types

Back 53

byte
short
int
long

Front 54

the two types for floating-point numbers

Back 54

float
double

the 'double' type is twice as big as 'float.' so the 'double' is known as double precision, 'float' as single precision.

Front 55

numeric operators

Back 55

the operators for numeric data types include the standard arithmetic operators:

addition (+)
subtraction (-)
multiplication (*)
division (/)
remainder (%)

Front 56

integer devision

Back 56

When both operands of a division are integers, the result of the division is an integer.

For example, 5/2 yields1, not 2.5

To perform regular mathematical division, one of the operands must be a floating-point number.

For example, 5.0/2 yields 2.5

Front 57

unary operator

Back 57

a unary operator has only one operand

( the + and - operators can be both unary and binary)

Front 58

binary operator

Back 58

a binary operator has two operands

( the + and - operators can be both unary and binary)

Front 59

floating-point approximation

Back 59

calculations involving floating-point numbers are approximated because these numbers are not stored with complete accuracy

integers are stored precisely, therefore calculations with integers yield a precise integer result

Front 60

literal

Back 60

a constant value that appears directly in a program

Front 61

long literal

Back 61

to denote an integer literal of the 'long' type, append the letter L to it

2147483648L because 2147483648 exceeds the range for the 'int' value

Front 62

floating-point literals

Back 62

written with a decimal point

treated as a 'double' type value

for example, 5.0 is considered a 'double' value, not a 'float' value

suffix f or F:
you can make a number a 'float' by appending the letter F

suffix d or D:
you can make a number a 'double' by appending the letter D

Front 63

double vs. float

Back 63

the 'double' values are more accurate than 'float' values

Front 64

scientific notation

Back 64

floating-point literals can also be specified in scientific notation; for example,

1.23456e+2 is equivalent to 1.23456 X 10(2) [squared]

1.23456e-2 is equivalent to 1.23456 X 10(-2)

Front 65

'E' or 'e'

Back 65

represents an exponent and can be in either lowercase or uppercase

Front 66

why called floating-point?

Back 66

The 'float' and 'double' types are used to represent numbers with a decimal point. Why are they called 'floating-point numbers'? These numbers are stored in scientific notation. When a number such as 50.534 is converted into scientific notation, such as 5.0534e+1, its decimal point is moved (i.e., floated) to a new position.

Front 67

evaluating an expression

Back 67

Java follows Please Excuse My Dear Aunt Sally.

Front 68

integer vs. decimal division

Back 68

Be careful when applying division. Division of two integers yields an integer in Java. 5/9 is translated to 5.0/9instead of 5/9, because 5/9 yields 0 in Java.

Front 69

currentTimeMillis

Back 69

The currentTimeMillis method in the System class returns the current time in milliseconds elapsed since the time 00:00:00 on January 1, 1970 GMT (the Unix epoch).

Front 70

Unix epoch

Back 70

1970 was the year when the Unix operating system was formally introduced.

00:00:00 on January 1, 1970

Front 71

System.currentTimeMillis()

Back 71

returns the number of milliseconds since the Unix epoch

you can use this method to obtain the current time, and then compute the current second, minute, and hour

Front 72

shorthand operators

Back 72

Java allows you to combine assignment and numeric operators using a shorthand operator

there are no spaces in the shorthand operators. for example, + = should be +=

Front 73

Operator:

+=

Back 73

Name:
addition assignment operator

Example:
i += 8

Equivalent:
i = i + 8

Front 74

Operator:

-=

Back 74

Name:
subtraction assignment operator

Example:
i -= 8

Equivalent:
i = i - 8

Front 75

Operator:

*=

Back 75

Name:
multiplication assignment operator

Example:
i *= 8

Equivalent:
i = i * 8

Front 76

Operator:

/=

Back 76

Name:
division assignment operator

Example:
i /= 8

Equivalent:
i = i / 8

Front 77

Operator:

%=

Back 77

Name:
remainder assignment operator

Example:
i %= 8

Equivalent:
i = i % 8

Front 78

assignment operator --> assignment statement

Back 78

Like the assignment operator (=), the operators (+=, -=, /=, %=) can be used to form an assignment statement as well as an expression. For example, i the following code, x += 2 is a statement in the first line and an expression in the second line.

x += 2; // Statement
System.out.println(x += 2); // Expression

Front 79

incrementing and decrementing a variable by 1

Back 79

two shorthand operators:

++ // Incrementing a variable by 1

-- // Decrementing a variable by 1

prefix or suffix

Front 80

Operator:

++var

preincrement

Back 80

Description:
Increment var by 1 and use the new var value

Example (assume i = 1):
int j = ++i; // j is 2,
// i is 2

Front 81

Operator:

var++

postincrement

Back 81

Description:
Increment the var by 1 and use the original var value

Example (assume i=1):
int j = i++; // j is 1,
// i is 2

Front 82

Operator:

--var

predecrement

Back 82

Description:
Decrement the var by 1 and use the new var value

Example (assume i = 1):
int j = --i; // j is 0,
// i is 0

Front 83

Operator:

var--

postdecrement

Back 83

Description:
Decrement the var by 1 and use the original var value

Example (assume i = 1):
int j = i--; // j is 0,
// i is 0

Front 84

if the operator is before (prefixed to) the variable

preincrement operator

Back 84

the variable is incremented or decremented by 1, then the new value of the variable is returned

Front 85

if the operator is after (suffixed to) the variable

postincrement operator

Back 85

the variable is incremented or decremented by 1, but the original old value of the variable is returned

Front 86

loop statement

Back 86

a construct that controls how many times an operation or sequence of operations is performed in succession

the increment operator ++ and the decrement operator -- can be applied to all integer floating-point types

More on this in Chapter 4

Front 87

Can you perform binary operations with two operands of different types?

Back 87

Yes. If an integer and a floating-point number are involved in a binary operation, Java automatically converts the integer to a floating-point value.

So, 3 * 4.5 is the same as 3.0 * 4.5

Front 88

type casting

Back 88

an operation that converts a value of one data type into a value of another data type

casting does not change the variable being cast

Front 89

widening a type

Back 89

casting a variable of a type with a small range to a variable of a type with a larger range

like ordering a tall coffe in a grande cup at Starbucks

Front 90

narrowing a type

Back 90

casting a variable of a type with a large range to a variable of a type with a smaller range

moving from the country to the city - in regards to physical space

moving from the city to the country - in regards to diversity

Front 91

type casting syntax

Back 91

The syntax is the target type in parentheses, followed by the variable's name or the value to be case. For example, the following statement:

System.out.println((int) 1.7);

displays 1. When a 'double' value is cast into an 'int' value, the fractional part is truncated.

The following statement

System.out.println((double) 1/2);

displays 0.5, because 1 is cast to 1.0 first, then 1.0 is divided by 2. However, the statement

System.out.println(1 / 2);

displays 0, because 1 and 2 are both integers and the resulting value should also be an integer.

Front 92

pow(a, b) method

Back 92

The pow(a, b) method in the Math class can be used to compute a(b) [a to the b power]

Example:
System.out.println(Math.pow(2, 3)); // Display 8
System.out.println(Math.pow(4, 0.5)); // Display 4

Front 93

char type

Back 93

The character data type, 'char', is used to represent a single character.

Front 94

character literal

Back 94

A character literal is enclosed in single quotation marks:

char letter - 'A';
char numChar - '4';

The first statement assigns character A to the char variable letter. The second statement assigns digit character 4 to the char variable numChar.

"A" is a string, and 'A' is a character.

Also, letters are equiv. to Unicode here

Front 95

character encoding

Back 95

Mapping a character to its binary representation

Front 96

encoding scheme

Back 96

the different ways in which characters are encoded

Front 97

Unicode

Back 97

Java supports Unicode, an encoding scheme established by the Unicode Consortium to support the interchange, processing, and display of written texts in the world's diverse languages.

Front 98

original Unicode

Back 98

Unicode was originally designed as a 16-bit character encoding

The primitive data type 'char' was intended to take advantage of this design by providing simple data type that culd hold any character

Front 99

supplementary characters

Back 99

original Unicode only had 65,536 possible characters in 16-bit encoding.

This was not sufficient for the world's characters, so they expanded to allow 1,112,064 characters

Front 100

prefix \u

Back 100

a 16-bit Unicode takes two bytes, preceded by '\u' expressed in four hexadecimal digits that run from '\u0000' to '\uFFFF'

Front 101

ASCII

Back 101

American Standard Code for Information Interchange

a 7-bit encoding scheme for representing all uppercase and lowercase letters, digits, punctuation marks, and control characters

Front 102

escape sequence for special characters

Back 102

Java defines escape sequences to represent special characters

begins with the backslash character (\) followed by a character that has a special meaning to the compiler

Front 103

Character Escape Sequence:

\b

Back 103

Name:
backspace

Unicode Code:
\u0008

Front 104

Character Escape Sequence:

\t

Back 104

Name:
tab

Unicode Code:
\u0009

Front 105

Character Escape Sequence:

\n

Back 105

Name:
linefeed

Unicode Code:
\u000A

Front 106

Character Escape Sequence:

\f

Back 106

Name:
formfeed

Unicode Code:
/u000C

Front 107

Character Escape Sequence:

\r

Back 107

Name:
Carriage Return

Unicode Code:
\u000D

Front 108

Character Escape Sequence:

\\

Back 108

Name:
backslash

Unicode Code:
\u005C

Front 109

Character Escape Sequence:

\'

Back 109

Name:
Single Quote

Unicode Code:
\u0027

Front 110

Character Escape Sequence:

\"

Back 110

Name:
Double Quote

Unicode Code:
\u0022

Front 111

implicit and explicit casting

Back 111

Implicit casting
double d = 3; (type widening)

Explicit casting
int i = (int)3.0; (type narrowing)
int i = (int)3.9; (Fraction part is truncated)