1. Chapter 2 Basic Computation
© Bobby Hoggard, Department of Computer Science, East Carolina University / These slides may not be used or duplicated without permission

2. Screen Output System.out =
In Java the screen is represented by the object:
System.out
The screen object contains the following methods for displaying output:
println() – prints what is inside the parentheses, with a line break at the end
print() – prints what is inside the parentheses, with no line break
Java Program
Physical Hardware
System.out =

3. Screen Output Source code Program output
System.out.println("Hello"); System.out.println("World");
Hello World
Hello
World
Line-Break
Line-Break
System.out.println("Hello"); System.out.println("World");
Note: Number of lines of source code have no relationship to the number of lines of output!

4. Screen Output Source code Program output
System.out.println("Hello"); System.out.println("World");
Hello
World
Line-Break
Line-Break
Hello
World \n
System.out.println("Hello\nWorld"); \n
Note: The "\n" character in Java represents the "Enter" key

5. Screen Output Source code Program output
Hello
World
System.out.println("Hello"); System.out.println("World"); \n \n
Adds line break at the end of the line
System.out.print("Hello\n"); System.out.print("World\n");
but, WE have added line
breaks in our output
Does NOT add line break at the end of the line
Note: The "\n" character in Java represents the "Enter" key

6. Screen Output Source code Program output Hello \n
World
System.out.println("Hello"); System.out.println("World"); \n \n
System.out.print("Hello\n"); System.out.print("World\n");
System.out.print("Hello\n"); System.out.println("World");
System.out.println("Hello\nWorld");

7. Screen Output Source code Program output
System.out.print("Hello"); System.out.println("World");
HelloWorld \n
Does NOT add line break at the end of the line
System.out.print("Hello");
Does NOT add line break at the end of the line
Note: Number of lines of source code have no relationship to the number of lines of output!

8. Screen Output Source code Program output Add space here
System.out.print("Hello"); System.out.println("World");
HelloWorld \n
Add space here
System.out.print("Hello "); System.out.println("World");
Hello World \n
System.out.print("Hello"); System.out.println(" World");
or add space here
Note: Number of lines of source code have no relationship to the number of lines of output!

9. Variables Memory locations that a program can use to store data
Variables must be declared before they can be used – variable declaration
To declare a variable, the programmer must:
Choose a name to represent the memory location – variable name
State the type of data that will be stored in the variable – data type
After declaration, to use the variable, you only need to type it's name – not it's data type
You cannot re-declare a variable, or change it's data type later

10. Variable Declaration Examples
data type
variable name
int n1;
int n1;
...
double n1;
int n1;
...
int n1;
...
System.out.print(int n1);
Variable Redeclaration
States that n1 should hold integers, but later states it should hold something else
Variable Redeclaration
States that n1 should hold integers, but later tries to declare n1 again
Variable Redeclaration
Just use the variable name; no need to try to specify it's data type again

11. Assignment Statements
Assignment Operator
Assignment statements use the assignment operator to store a value into a variable
It works by taking the "stuff" on the right side of the operator, and places it into the variable on the left side of the operator ;
Variable
Stuff to store in variable
Note: A single variable name ALWAYS appears on the left side of an assignment operator

12. What Can You Store? x 1 1 x 1 3 y x 3 3 LITERALS
int x;
LITERALS
(simple, unchanging values) x 1 1
x = 1;
CALCULATED ANSWERS x
calculate: 1+2
answer is 3 1 3
x = 1 + 2;
VALUE FROM ANOTHER VARIABLE y x
int y;
y = x; 3 3
retrieve value from x
store into y

13. What Can You Store? x 3 4 x 4 39 retrieve value of x value of x is 3
int x = 3; Scanner kbd = new Scanner(System.in);
CALCULATIONS INVOLVING VARIABLES
retrieve value of x
value of x is 3
calculate 3 + 1
answer is 4
store 4 back into x x 3 4
x = x + 1;
VALUES RETRIEVED FROM A METHOD
retrieve value from keyboard
assume user enters 39 x 4 39
x = kbd.nextInt();
Note: Assume the keyboard has been properly declared and initialized in all future examples!

14. What Can't You Do? Use an undeclared variable anywhere in your program
int x;
Use an undeclared variable anywhere in your program
z = 1;
Error: z cannot be resolved to a variable
Declare all variables before attempting to use them
int z; z = 1;
Use an uninitialized variable
int z;
x = z + 2;
Error: The local variable z may not have been initialized
A variable must have a value before you attempt to READ it's value
int z = 3; x = z + 2;

15. Printing Variable Values
Source code
Program output
int x = 5;
System.out.println("x"); x
System.out.println(x); 5
System.out.print("x = "); System.out.println(x);
x = 5
System.out.println("x = " + x);
x = 5
Note: Literal data inside double quotes (") is called a String

16. print/println ONLY prints Strings
expression
HOW TO "Calculate"
int x = 5;
System.out.println("x = " + x);
retrieve the value of x
System.out.println("x = " + 5);
convert int 5 to a String
System.out.println("x = " + "5");
Strings must be concatenated
System.out.println("x = 5");
print String to the screen: x = 5
Note: Concatenate means to join together

17. "+" for Addition int int add
System.out.println(1 + 2);
int
int
add
System.out.println(1 + 2);
calculate 1 + 2
System.out.println(3);
int 3 must be converted to String
System.out.println("3");
Print String to the screen: 3
Note: + performs addition if there is a number on both sides of the operator

18. "+" for Concatenation String String concatenation
System.out.println("1" + "2");
String
String
concatenation
System.out.println("1" + "2");
concatenate the Strings
System.out.println("12");
Print String to the screen: 12
Note: + performs concatenation if there is a String involved

19. "+" With Mixed Types
System.out.println( " is the answer");
Prints: 3 is the answer
System.out.println( " is the answer");
+ is applied left to right
System.out.println((1 + 2) + " is the answer");
add 1 + 2
System.out.println(3 + " is the answer");
convert int 3 to String
System.out.println("3" + " is the answer");
concatenate the Strings
System.out.println("3 is the answer ");
Print String to the screen: 3 is the answer
Note: + performs addition ONLY if there is a number on both sides of the operator

20. What Does This Print? System.out.println("The answer is " + 1 + 2);
Prints: The answer is 12
System.out.println("The answer is " );
+ is applied left to right
System.out.println(("The answer is " + 1) + 2);
convert int 1 to String
System.out.println(("The answer is " + "1") + 2);
concatenate the Strings
System.out.println("The answer is 1" + 2);
convert int 2 to String
System.out.println("The answer is 1" + "2");
concatenate the Strings
System.out.println("The answer is 12");
Print String to the screen: The answer is 12

21. Variable Names
Note: Variable names SHOULD start with a lowercase letter
Programmers are free to choose whatever names they like for their variables The only rules for variable naming are as follows:
NO KEYWORDS
Variable names cannot be the same as a Java defined keyword
int class;
int cLass;
START WITH A LETTER OR UNDERSCORE
Variable names must start with an alphabetic letter or the underscore (_)
int 3pay;
int pay3;
USE ONLY LETTERS, NUMBERS, OR UNDERSCORES
After the 1st character, variable names can only contain letters, numbers and underscore (_) characters
int pay rate;
int pay_rate;
int payRate;

22. Primitive Data Types byte short int long float double char boolean
CHARACTERS
REAL
WHOLE
TRUE / FALSE
NUMERIC TYPES
Note: Primitives hold a single value / Objects CAN hold multiple values

23. Whole Number Data Types
Space Required For Storage
Range *
int
4 bytes -
2,147,483,648
to +2,147,483,647
short
2 bytes -
32,768 to +32,767
byte
1 byte -
128 to +127 -
9,223,372,036,854,775,808 to
long
8 bytes
+9,223,372,036,854,775,808
Note: Whole numbers are stored in 2's compliment notation
* int is the default whole number data type

24. Real Number Data Types ± 1.79769313486231570 x 10 to * double 8 bytes
Space Required For Storage
Range
x 10
+308 to *
double
8 bytes
x 10 -
324
x 10
+38 to
float
4 bytes
x 10 - 45
Note: These variable values are stored in floating point notation
* double is the default real number data type

25. Other Data Types char 2 bytes Unicode values from 0 to 65,535 boolean
Space Required For Storage
Range
char
2 bytes
Unicode
values from
0 to 65,535
boolean
1 byte
The values:
false or
true

26. Data Type Literals
Single character (char) literals are surrounded by single quotes ( ' )
Multiple character ( String ) literals are surrounded by double quotes ( " )
Numbers are not surrounded by any special characters
char letter = 'A';
char letter = "A";
String name1 = 'Andy'; String name2 = 'A';
String name = "Andy";
int num1 = "39"; int num2 = '39';
int num = 39;

27. Test Your Knowledge Source code Program output int x = 5;
System.out.println( x ); 5
System.out.println( "x" ); x
System.out.println( 'x' ); x
x = 1 + 2; System.out.println( x ); 3
x = "1 + 2";
Type mismatch: cannot convert from String to int
System.out.println( '1' + '2' ); 99

28. Why Not Concatenation? char 2 bytes Unicode values from 0 to 65,535
System.out.println( '1' + '2' ); 99
char
char
Note: + performs concatenation
if there is a String involved
char
2 bytes
Unicode
values from
0 to 65,535
Note: char values are actually stored in memory as numbers (a Unicode value)

29. Type Compatibilities Is 1 equivalent to "1" ? Is 1 equivalent to '1' ?
Strings are objects
ints are primitives
int
String
Although, both are primitives, and both are numbers, the character '1' is not stored in memory as the number 1
Is equivalent to '1' ?
int
char
The Unicode value for the character '1' is the number 49
Is equivalent to '1' ?

30. asciitable.com
The ASCII table is a smaller subset of the larger Unicode table
(and easier to read for our purposes)

31. '1' is equivalent to the number 49
System.out.println( '1' + '2' );
substitute values
System.out.println( );
add
System.out.println( 99 );
convert to String
System.out.println( "99" );
Prints: 99

32. We have already established that '1' + '2' equals the number 99
System.out.println( '1' + '2' );
Prints: 99
char ch = '1' + '2';
System.out.println( ch );
Prints: c
We have already established that '1' + '2' equals the number 99
The number 99 is equivalent to the character 'c'

33. char ch = '1' + '2';
System.out.println( ch );
int num = '1' + '2';
System.out.println( num );
Prints: c
Prints: 99
ch and num are both holding the same value in memory (which is 99) BUT…
character, you expect to see a character
If you ask Java to print a
integer, you expect to see an integer
If you ask Java to print an

34. Thinking Outside the Box!
Example: Print the string "ABCD" to the screen
Obvious answer
Not so obvious answer
System.out.println( "ABCD" );
char ch = 'A'; System.out.print( ch ); ch = ch + 1; System.out.print( ch ); ch = ch + 1; System.out.print( ch ); ch = ch + 1; System.out.println( ch );

35. char ch = 'A';
System.out.print( ch );
ch = ch + 1;
System.out.println( ch );
store 65 into ch
print 'A'
ch = ;
print 'B'
ch = ;
print 'C'
ch = ;
print 'D';
ch = 65
ch = 66
ch = 67
ch = 68
Prints: ABCD \n

36. Review of Data Types Is 5 equivalent to 5.0 ? int 5
Primitive: 2's compliment
8.6
double
Primitive: Floating point
'x'
Primitive: Unicode
char
String
"x"
Object (containing multiple Unicode chars)
Is equivalent to ?
2's compliment
Floating point

37. Automatic Type Conversion
Java will automatically convert from a small data type to a larger data type
byte short int long float double
Automatic Conversion
No Automatic Conversion

38. Automatic Type Conversion
double x;
x = ;
double x;
x = 5.0;
double x;
x = 5;
Auto type convert:
double = int
Type match:
double = double
Type match:
double = double
double
5.0
int 5
x = 5.0;

39. When Auto Type Conversion Doesn't Work
int y;
y = 5;
int y;
y = 5.0;
Type match:
int = int
Type Mismatch:
int = double
int 5
double
5.0
Note: Auto conversion does not work
when going from a large type
to a smaller type

40. (desiredType) valueToConvert
Type Casting
Type casting allows us to change primitive data type into another primitive type
Syntax:
(desiredType) valueToConvert
int y;
y = (int)5.0;
int 5
double
5.0

41. double-to-int Type Casting
When converting from floating point data types to whole number data types, the decimal places are simply truncated – NOT rounded.
int y;
y = 5.1;
int y;
y = (int)5.1;
int y;
y = (int)5.9;
Type Mismatch:
int = double
Type match:
int = ( int  double )
Type match:
int = ( int  double ) y y 5 5

42. Type Compatibilities Source code Program output
int x = 'B'; char y = 65;
System.out.println( x ); 66
System.out.println( y ); A
y = 'A'; System.out.println( y ); A
System.out.println( (int)y ); 65
System.out.println( (char)x ); B

43. Java Math Operators + - * / % num + num a * b a . b
* / %
add
subtract
multiply
divide
modulus
num + num
returns the remainder
from a division
a * b
concatenate
a . b
String + num num + String String + String
a ( b )

44. Java Math & Data Types 2 + 3 = 5 2 + 3.1 = 5.1
Math involving two of the same data type, produces an answer with the same data type =
int
int
int
Math involving mixed data types, produces an answer which is the larger of the two data types =
int
double
double
Automatic Conversion
byte short int long float double

45. Java Math & Data Types 7 / 3 = 2.333 7 / 3 = 2
Math involving two of the same data type, produces an answer with the same data type
/ =
int
int
double
/ =
int
int
int

46. Java Math & Data Types 7 / 3 = 2 7 / 3.0 = 2.333
Math involving two of the same data type, produces an answer with the same data type
/ =
int
int
int
Math involving mixed data types, produces an answer which is the larger of the two data types
/ =
int
double
double

47. Java Math & Data Types 7 / 3.0 = 2.333 7.0 / 3 = 2.333
/ =
/ =
/ =

48. Java Math & Data Types 7 / 3 = 2 7 3 2 r1 6 1 7 % 3 = 1
The "/" operator produces the quotient from long division
/ = 7 3 2 r1 6 1
The "%" operator produces the remainder from long division
% =

49. amount of money to change
Division Example
We need to give change for $0.13. We only have nickels and pennies available.
How many nickels and how many pennies do we give?
/ =
2.6
2.6 nickels
?? pennies
amount of money to change
value of nickel
Do integer division, and get the quotient and remainder
13 / = 2
2 nickels
13 % = 3
3 pennies

50. Test Your Knowledge What value will be stored in x? x = 2.0 1 2 3 4
int a = 7;
int b = 3;
double x;
x = a / b;
double = int / int 2
x = 2;
double = int
x = 2.0 3
x = (double)2;
double = double 4
x = 2.0;
double = double

51. Produce a double with Type Casting
x = a / 3.0;
x = 2.333
int a = 7;
int b = 3;
double x;
double = int / double
x = a / b;
x = 2.0
double = int / double
x = a / (double)b;
x = 2.333
double = int / double
x = (double)a / b;
x = 2.333
double = double / int

52. Test Your Knowledge What value will be stored in x? x = 2.0
int a = 7;
int b = 3;
double x;
x = (double)(a / b);
x = (double)(a / b);
manual type casting
double = (double)(int/int)
x = / 3;
x = 2.0
automatic type casting
double = int / int

53. Operators & Commands
Operators – produce a mathematical value that can be used in a larger equation
Commands – cause some type of change in the program (usually change a variable's value)
x = ;
command
operator
store 3 into x
add 1 and 2 to produce 3
but also an operator
produces the same value stored in the variable

54. Operator Examples int x, y; x = 3 + ( y = 7 ) + 1; Precedence: () + =
11;
the 11 is discarded

55. ERROR: y is uninitialized
Operator Examples
int x, y;
x = y = ;
Precedence: () + =
ERROR: y is uninitialized
Compiler error: program will not compile

56. Operator Examples int x = 1; x = 2 + x + (x = 5) + 1; x = 513
the 13 is discarded

57. Operator Examples int x, y, z; x = 7; y = 7; z = 7; x = y = z = 7;

58. Increment/Decrement Operators/Commands
Used to change a variable's value by adding 1, or subtracting one, from a variable.
int x = 1;
Increment
Decrement
x++;
Postfix
x--;
++x;
Prefix
--x;

59. Prefix vs. Postfix The difference is WHEN the increment takes place
int x = 1;
Postfix
Prefix
x++;
++x;
perform calculations with OLD value
Get value of x
Add one to x
Add one to x
Get value of x
perform calculations with NEW value

60. Operator Examples int x, y; x = 5; y = 2 + ++x; x = 6 y = 2 + x++;

61. Operator Examples int x, y; x = 5; y = 2 + x++ + 1 + x; x = 6
Postfix: use OLD value, then increment
y = x;
y = x;
y = ;
Remember: x changed values on line 1
y = 14;

62. Shortcut Operators
Perform a math operation AND change a variable's value
SHORTCUT OPERATOR
EQUIVALENT OPERATION
x += 7;
x = x + 7;
x -= 2;
x = x - 2;
x *= 3;
x = x * 3;
x /= 5;
x = x / 5;
x %= 4;
x = x % 4;

63. Shortcut Operator Examples
DESIRED EQUATION
EQUIVALENT OPERATION
x = x + (y * 3);
x += (y * 3);
x += y * 3;
x = x x;
x += ++x;

64. Equivalent Examples
GOAL: Add 1 to x
x = x + 1;
x++;
++x;
x += 1;