1. Assignments, Expressions & Operators
Joe McCarthy
CSS 161: Fundamentals of Computing

2. CSS 161: Fundamentals of Computing
Recap: Intro to Java
Class
Method
main()
Identifier
Reserved word
Variable
Declaration
Assignment
Operator
System.out.println()
Output:
= 30
CSS 161: Fundamentals of Computing

3. CSS 161: Fundamentals of Computing
Memory organization
CSS 161: Fundamentals of Computing

4. CSS 161: Fundamentals of Computing

5. Assignments & Expressions
Syntax:
variable = expression
Semantics:
Evaluate expression, assign value to variable
Expression:
Constant (1, 1.23, 3.45e6, ‘a’, “css161”, true, false)
final static int COURSENUMBER = 161;
Variable (totalScore)
expression operator expression
Operators:
*, /, %
+, - …
All lower case
Convention: ALL CAPS for constants
Convention: camelCase for variables
CSS 161: Fundamentals of Computing

6. Operators & Precedence
Can use parentheses to change precedence
1 + 2 * 3
(1 + 2) * 3
CSS 161: Fundamentals of Computing

7. CSS 161: Fundamentals of Computing

8. Shorthand assignments
Example:
Equivalent To:
count += 2;
count = count + 2;
sum -= discount;
sum = sum – discount;
bonus *= 2;
bonus = bonus * 2;
time /=
rushFactor;
time =
time / rushFactor;
change %= 100;
change = change % 100;
amount *=
count1 + count2;
amount = amount * (count1 + count2);
CSS 161: Fundamentals of Computing

9. Increment & Decrement Operators
Syntax:
variable++ | ++variable | variable-- | --variable
Semantics:
Set variable to next / previous value
Examples
int num1 = 1; char char1 = ‘B’;
num1++;
char1--;
Precedence: increment/decrement before/after use
2*(num1++)  2
2*(++num1)  4
CSS 161: Fundamentals of Computing

10. Assignment Compatibility
byteshortintlongfloatdouble
char
CSS 161: Fundamentals of Computing

11. Type casting & coercion
Syntax:
variable = (type) expression
Semantics
Cast (convert) expression to type, assign value to variable
Only allowed if expression type is compatible with variable type
Type coercion:
Automatic type casting: int  float  double
Examples
short num3 = ‘A’; // 65 = ASCII code for ‘A’
int num4 = (int) 1.9;
double num5 = 123; // coercion
int num6 = 1.23; // error
CSS 161: Fundamentals of Computing