Java Basics: Variables, Assignments, Operators

Names of variables, functions, classes (all user defined objects), Identifiers: 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 andRate 1 123 No numbers ITK 168

A variable: A name of a location in memory to hold value A value of what? •  11110101 int a; String A; 245  0010 0010 0010 0100 0010 0101 • the name • the type • the value ITK 168

Text String Binary: 0101 0100 0110 0101 0110 1100 0010 1010 0010 0000 0011 0010 0011 0010 0011 1000 0011 0111 0011 0010 0011 0100 0011 1001 ITK 168

http://www.dynamoo.com/technical/ascii.htm ASCII American National Standard Code for Information Interchange • 7-bit code ITK 168

Numbers inside Computers Java’s Types short int long float double ITK 168

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. ITK 168

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. ITK 168

L-value = R-value Assignment examples 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 = 3/2.0-0.5; 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") ITK 168

More on Assignments 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); ITK 168

Parameter Passing formal parameters int plus (int a, int b) { return a+b; } int x = plus(1,2); function body • How are parameters passed? • Looks simple enough… • There are some techniques actual parameters (arguments) function call ITK 168

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 ITK 168

Parameter Passing int minus (int a, int b) { return a - b; } int x = minus(1, 2); function call 1  a 2  b ITK 168

Local variables int minus (int a, int b) { int x = a – b; return x; } publicstaticvoid main(String[] args) { .... int a = 3; int b = 2; int d = 0; int x = a+b; d = minus(b,a); ..... } ITK 168

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 JavaResulting true or false < <= > >= == != && || ! & | ^ (20 < y) && (x <= i) ITK 168

|| && ! Logical Operators Assume x = 10 true (1 || 0) ((18 <= x) && (x <= 50)) ((18 <= x) || (x <= 50)) !(x < 5) is same as (x >= 5) (((x % 2) == 0) && ((x % 3) == 0)) false true true false ITK 168

Java Basics: Variables, Assignments, Operators