1. Java Basics

2. Java High-level language Designed by Sun Microsystems in 1995
More readable for humans
Need to be translated to machine language for execution
Compilers
CPU-independent
translation can target different CPUs (machine languages)
Designed by Sun Microsystems in 1995
Sun was bought by Oracle in 2010
Designed with internet in mind
Can run in a web browser

3. Storing Data To store data we need to allocate space in the memory
Declare (specify)
Type
what kind of data
Name
we can refer to it later
Essentially a named location in the memory

4. Types int double boolean char (signed) integer
double-precision floating point number
boolean
true or false
char
character

5. Names (“Identifiers”)
Starts with a letter
After that, can include
letter
digit
Can these be names?
numberOfStudents
five5 55
5five
Case sensitive
Balance and balance are different names
Meaningful names improve readability
reduce mistakes

6. The Famous/Weird Semicolon
Is similar to a period after a sentence in English
End of one instruction
Period is used to mean something else in Java
Allocating space (“declaration”):
int numberOfStudents;
double temperature, humidity, pressure;
boolean sunny, hurricane;
char letterGrade;
They are usually called variables similar to math
How do we vary/change the value?

7. Changing Values Assignment x = 97.5; =
Equal sign, but doesn’t mean equal as in math
x = 97.5;
Means assign 97.5 to x (or store in x)
Doesn’t mean we state x is equal to 97.5

8. Changing Values Assignment x = 97.5; x = 97.5 + x; =
Equal sign, but doesn’t mean equal as in math
x = 97.5;
Means assign 97.5 to x (or store in x)
Doesn’t mean we state x is equal to 97.5
x = x;
Why is this impossible in math?
What does this mean in Java?

9. Changing boolean and char variables
boolean sunny;
sunny = false;
char letterGrade;
letterGrade = ’A’;

10. Initializing Variables
Combining
Declaring a variable (allocating space) and
Assigning an initial value
int numberOfStudents = 15;
double gpa = 3.14;
char letterGrade = ’A’;
boolean sunny = true;

11. Manipulating Data
Operators
Arithmetic
Relational
Logical

12. Arithmetic Operators + - * / % ++x , x++ Yields a number
modulo/reminder
5 % 2 is 1
++x , x++
Increment x (int)
Yields a number

13. Arithmetic: Division with Integers
Math: 5 / 2 is 2.5
Java
“integer division”—both values/operands are integers
5 / 2 has an integer value -- floor of 5/2
5 / 2 is 2 [sometimes this is useful]
If we want a floating point value (2.5)
5 / 2.0 , 5.0 / 2 , or …
Be careful
int x = 5 / 2.0 ;
x has 2 because 2.5 can’t fit into an int variable

14. Relational Operators < <= > >= == !=
Yields true or false value
5 < 2
yields false
not stating 5 is less than 2 (in math), which is impossible
x == 2
Means what?

15. Logical Operators && || ! Yields true or false value and or not
true && false is false
!(5 > 2) is false

16. && (and) operator
Green
(boolean)
Square
Green && Square F T

17. || (or) operator
Green
(boolean)
Square
Green || Square F T

18. ! (or) operator
Green
(boolean)
!Green F T

19. Precedence/Ordering of Operators
x < y + z
(x < y) + z
x < (y + z)

20. Precedence/Ordering of Operators
x < y + z
(x < y) + z
x < (y + z)
x < y + z && y < z
x < (y + z) && y < z
((x < (y + z)) && y) < z
(x < (y + z)) && (y < z)

21. Precedence/Ordering of Operators
Quite natural
Arithmetic (calculate numbers) before
Relational (compare numbers) before
Logical (combine boolean--true/false values)
If not sure, add parentheses

22. Comments Ignore by the compiler
Improves readability, fewer mistakes
// describe something that is not obvious
/* this is a
multi-line comment */

23. Math Constants and Functions
Math.PI, Math.E
Math.abs(x)
Math.sqrt(x), Math.pow(x, exp)
Math.log(x), Math.log10(x)
Math.sin(x), Math.cos(x), Math.tan(x) // radians
Math.asin(x), Math.acos(x), Math.atan(x)
Math.random() // 0 <= num < 1

24. Input from the Keyboard
We’ll usually provide templates for input
Scanner keyboard = new Scanner(System.in);
x = keyboard.nextInt();
y = keyboard.nextDouble();

25. Output to the Screen System.out.println( … ); System.out.print( … );
Print the parameter followed by a new line
Examples:
System.out.println(15);
System.out.println(x);
System.out.println(“Hello!”); // “string”
System.out.print( … );
Print the parameter without a new line