todaysnotes.md

Variables

Is that a Variable!?

ex: j, myVar, _inT

Back to _inT, this is a bad variable because it uses a reserved word, and had a leading underscore, which should only be used for device drivers, and lower level system development.

• Another example of a bad variable is password$, this is because the $ indicates security.

• @ is not a variable in Java, but may be a variable in other languages.

• i j, k, m, n, p, q, r, x, y are temporary variables they should NOT be used for important variables.

• i and j are incrementors and decrimentors.

Recap:

• _ before a variable, ex: _var should be reserved for low level development.
• $ before a variable, ex: $var should be reserved for security development.

Variable Declarations

Primative types in Java

Type	Size in Bytes	Range
byte	1 byte	128-127
short	2 bytes	-32,768 to 32,767
char	2 bytes	0 to 65,536
int	4 bytes	-2,147,483,648 to 2,147,483,647
float	4 bytes	±3.40282347E+38F
long	8 bytes	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
double	8 byte	±1.79769313486231570E+308
boolean	not defined	true or false

Explicit value assignment

• null A quantity whose specific value is undefined. the reserved word null is case sensitive.

• String Is always denoted using double quotations (""). Two double quotations used without any intervening characters denotes null

• Decimal (int) values - Is always denoted using double quotations (""). Two double quotations used without any intervening characters denotes null

• double any unqualified value that contains a decimal point. 1234.56 is a rational number treated as double.

• short instantiating a short must be done with respect to how the compiler treats the size of constant values.

• float a decimal number that is immediately proceeded by the character lowercase 'f'. Is a rational number treated as floating-point.

• char - a single symbol bounded by single quotation marks (''). Use of the numeric value zero as an initialization or an assignment to a char is convention that the character is null, even though it is not the null value. Note that two or more symbols in sequence consitutes a string.

Complex types in Java (defined by the comments //)

public class IntroToProg {
     int deen; // Declaration or instantiation.
     int deen = 0; // Declaration and initializatoin. 
     public static void main(String[] args) {
          deen = 0; // Assigning a instanted variable.
     }
}

• Declaration Specifying a data type and a name without giving it a starting value.

• Initialization A declaration using a starting value.

• Assignment When a value is given to a variable after its declaration or initialization. DOES NOT HAVE A TYPE

  • Lvalue = Rvalue

• Instantiate To create a variable or process and not initialize it.

teacher being annoying with number bases.

double example1 = 010.01; // This is equal to 10.01 in base 10.
double example2 = 0x12; // This is equal to 18 in base 10.

double example = 123f; // The jvm finna cast this.

• final Declaring that an entity can only be assigned a value ones in a scope.

• God Statement Declaring: mod type name value.

char digit = '0';
int x = digit - 48; // this int equals 0, you're subtracting by the ascii numeric representation of zero.

Conditions and Conditional Statements

Conditional Statements

• if Changing Branching conditional, changes the program flow.

• while Looping conditional, only interates while a condition is met.

• do Statement behaves similarly to the while() loop in that it iterates until the Boolean condition is false, except that the contents of the do-while() are guaranteed to execute at least once.

• switch Comparison of constant values.

• ternary (cond) ? T : F ; This is the only condition that uses assignment.

• for Iterative; repetition to to resolve a sequential outcome.

• else Only executes if the condition isn't met, continues program flow.

Constructing an if statement

// if (conditional)
// for exmple `!(Conditional)` is, the negation of the condition l -> r
// `&&` 2 operands l -> r
// || (x && y ) || (z || p)

boolean condition = false; 

if (!condition) {
    return;
}

Level	Operator	Description	Associativity
16	[] . ()	array element, object memebers, parentheses	left to right
15	++ --	unary post-increment, unary post-decrement	not associative
14	++ -- + - ! ~	unary pre-increment, unary pre-decrement, unary plus, unary minus, unary logical NOT, unary bitwise NOT	right to left
13	() new	cast, object creation	righ to left
12	* / %	multiplicative	right to left
11	+ - +	additive, string concatentation	left to right
10	<< >> >>>	shift	left to right
9	< <= > >= instanceof	relational	not associative
8	== !=	equality	left to right
7	&	bitwise AND	left to right
6	^	bitwise XOR	left to right
5	|	bitwise OR	left to right
4	&&	logical AND	left to right
3	||	logical OR	left to right
2	?:	ternary	right to left
1	= += -= *= /= %= &= ^= |= <<= >>= >>>=	assignment	right to left

Other stuff

int x = 4;
int p = 2

int y = x+++p--;

// y = 6 because (4 + 1) + (2-1) = 6 

// another example

int y = x+++p;

// the x operator has a higher level of associativity, and will result in y equating to 6