1. Names of variables, functions, classes
Identifiers:
Names of variables, functions, classes
(all user defined objects),
Examples: if
else
while
int
float
double
main
...
Can’t be used as identifiers
They are reserved word a b
gcd
GCD A
COSC1373
TAX
Tax_Rate
Tax Rate
No special chars
$ “ ; ,
...
Two identifiers,
Tax and Rate 1
123
No numbers
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2. A name of a location in memory to hold value
A variable:
A name of a location in memory to hold value
A value of what? 
int a;
String A;
245 
the name
the type
the value
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3. Text String Binary: Text T e l : 2 8 7 4 9 EBCDIC E3 85 93 7A 40 F2 F8
ASCII 54 65 6C 2A 20 32 38 37 34 39
Binary:
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4. ASCII American National Standard Code for Information Interchange
American National Standard Code for
Information Interchange
7-bit code
Arabic
ASCII
Binary
Hex 20 1 21 2 22 3 23 4 24 5 25 6 26 7 27 8 28 9 29
Char
ASCII
Binary
Hex a 61 b 62 c 63 …
……… A 41 B 42 C 43 ….
……. : 3A # 23
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5. Numbers inside Computers
Bits
Minimum
Maximum
Integers
Short
Signed 8
-128
127
Unsigned
255
Integer 16
-32,768
32,767
65,535
Long 32
-2,147,483,648
2,147,483,647
4,294,967,295
Range
Floating Points
Single
-3.410-38
3.41038
Double 64
-1.710-308
1.710308
Java’s Types
short
int
long
float
double
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6. 8 primitive data types in Java
short i,j;
int no;
long sum;
float total;
double tax;
char grade;
byte b;
boolean yes_or_no;
i = 3;
j = 3.14;
tax = 8.25/100;
grade = ‘A’;
grage = ‘B’;
grade = 97;
yes_or_no = true;
yes_or_no = false;
Every variable
has to be declared
before we use it.
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7. Variables and Assignments
Everything
that can
receive a
value
L-value = R-value
Everything
that can
give a
value
Assignment operator
variable
function
expression
literal
variable
The data types in both sides have
to be consistent.
If not, type-casting must be done.
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8. illegal Assignment examples L-value = R-value i = (3+7)*2-4-2*5; i =
3/2-0.5;
illegal
3 = j;
gcd(24,18) = 2+3;
i+1 = j+3;
i = 3/ ;
i =
i+2;
total = i+j;
average = total/2;
sum = average*10*tax_rate;
i = gcd(24,18);
i =
Integer.parseInt( );
JOptionPane.showInputDialog("Input y")
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9. More on Assignments L-value = R-value L-value = R-value L-value =
This operation itself
will give a value
L-value = R-value
L-value = R-value
L-value =
L-value =
a = b = c = i+j+3+gcd(15,6);
illegal: a = b+1 = c = i+j+3+gcd(15,6);
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10. Parameter Passing How are parameters passed? Looks simple enough…
formal parameters
int plus (int a, int b) {
return a+b; }
int x = plus(1,2);
function
body
actual parameters
(arguments)
function call
How are parameters passed?
Looks simple enough…
There are some techniques
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11. Parameter Correspondence
Which actual parameters go to which formal parameters?
Most common case: positional parameters
Correspondence determined by positions
nth formal parameter matched with nth actual
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12. Parameter Passing function call 1  a 2  b int minus (int a, int b) {
return a - b; }
int x = minus(1, 2);
function call
1  a
2  b
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13. Local variables int minus (int a, int b) { int x = a – b; return x; }
public static void main(String[] args) {
....
int a = 3;
int b = 2;
int d = 0;
int x = a+b;
d = minus(b,a);
..... }
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14. Arithmetic operators in Java
+ - * / %
(x % y) is the remainder of x divided by y
+ - * / %
(x % y) is the remainder of x divided by y
Relational and logical operators in Java Resulting true or false
< <= > >= == !=
&& || ! & | ^
(20 < y) && (x <= i)
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15. Logical Operators || && ! Assume x = 10 true false true true false
|| && !
Assume x = 10
(1 || 0)
((18 <= x) && (x <= 50))
((18 <= x) || (x <= 50))
!(x < 5) is same as (x >= 5)
(((x % 2) == 0) && ((x % 3) == 0))
true
false
true
true
false
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