Java Static Variables and Operators, Slides of Java Programming

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^ Static^

Variables

(class^ data

members)

^ Non‐^ static

Variables

(class^ instance

data

members

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The pi data exists and we can access it

even

when no instance

of MyMathStuff is created. We can access the data directly using the nameof the class, as in:double x = 2.0 * MyMathStuff.pi;

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^ We^ could

also^ define

static^ methods

that^ we

can^ call^ without

instantiating

the^ class.

For

example,

5

public class MyMathStuff{ public static double pi = 3.14;public static double timesPI (double x){ return x * pi;} }

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If a class property is also declaredclass MyMathStuff{ public final static double PI = 3.14;}

final^ it is referred to as a

constant^ since it cannot be altered:

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^ An^ identifier

is^ a^ sequence

of^ characters

that^ consist

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.

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final^ datatype

CONSTANTNAME

=^ VALUE;

final^ double

PI^ =^ 3.14159; final^ int

SIZE^ =^

3;

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Name^

Range^

Storage Size

byte^

(^7) –2(-128) to 2

7 –1 (127)^

8-bit signed

short^

(^15) –2(-32768) to 2

15 –1 (32767)^

16-bit signed

int^

(^31) –2(-2147483648) to 2

31 –1 (2147483647)

32-bit signed

long^

(^63 63) –2to 2–

64-bit signed

(i.e., -9223372036854775808to^ 9223372036854775807) float^

Negative range:

32-bit IEEE 754

-3.4028235E+38 to -1.4E-45Positive range:1.4E-45 to 3.4028235E+ double^

Negative range:

64-bit IEEE 754

-1.7976931348623157E+308 to-4.9E-324Positive range:4.9E-324 to 1.7976931348623157E+

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Calculations

involving

floating‐

point^ numbers

are

approximated

because^

these^ numbers

are^ not^ stored

with^ complete

accuracy.

For^ example,

System.out.println(1.

‐^ 0.1^ ‐^ 0.

‐^ 0.1^ ‐^ 0.

‐^ 0.1);

displays 0.5000000000000001, not 0.5, andSystem.out.println(1.

‐^ 0.9);

displays^ 0.09999999999999998,

not^ 0.1.^ Integers

are

stored^ precisely.

Therefore,

calculations

with^ integers

yield^ a^ precise

integer^ result.

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A^ literal^ is

a^ constant

value^ that

appears^ directly

in^ the^ program.

For^ example,

34,^ 1000000,

and

5.0^ are^ literals

in^ the^ following

statements:

int i = 34;long x = 1000000;double d = 5.0;

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16

Operator^ Name

Description

++var^ preincrement

The expression (++var) increments var by 1 and evaluatesto the

new^ value in var^

after^ the increment.

var++^ postincrement

The expression (var++) evaluates to the

original^ value in var and increments var by 1. --var^ predecrement

The expression (--var) decrements var by 1 and evaluatesto the^

new^ value in var^ after

the decrement.

var--^ postdecrement

The expression (var--) evaluates to the

original^ value in var and decrements var by 1.

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int^ i^ =^ 10; int^ newNum^ =

10 *^ i++ ;^

int^ newNum^ =

10 ^ i Same effect asi^ =^ i^ +^ 1; int^ i^ =^ 10; int^ newNum^ =^10 _^ ( **++i_** );^

i^ =^ i^ +^ 1;int^ newNum^

;= 10 * i Same effect as

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Implicit

castingdouble d^ =^ 3;^

(type^ widening) Explicit

castingint i =^ (int)3.0;

(type^ narrowing) int^ i^ =^

(int)3.9;

(Fraction

part^ is

truncated) What is wrong?

int x = 5 / 2.0;

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byte, short, int, long, float, double

range increases

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char letter = 'A'; (ASCII)char numChar = '4'; (ASCII)char^ letter

=^ '\u0041';

(Unicode)

char^ numChar

=^ '\u0034';

(Unicode)

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Four hexadecimal digits.

NOTE: The increment and decrement operators can also be usedon char variables to get the next or preceding Unicode character.For example, the following statements display character b.char ch = 'a';System.out.println(++ch);

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