1. Chapter 02
Data and Expressions

2. Contents 2. 1 Character Strings 2. 2 Variables and Assignment
2. 3 Primitive Data Types
2. 4 Expressions
2. 5 Data Conversion
2. 6 Interactive Programs
2. 7 Graphics
2. 8 Applets
2. 9 Drawing Shapes

3. System.out.println ("Whatever you are, be a good one.");
2. 1 Character Strings
String literal
example
"This is a string literal."
"123 Main Street"
"X"
defined by the String class
every string literal represents a String object
The print and println methods
System.out.println ("Whatever you are, be a good one.");
method
name
information provided to the method
(parameters)
object

4. 2. 1 Character Strings The print method String concatenation
the System.out object provides
the print method is similar to the println method, except that it does not advance to the next line
see Countdown.java (page. 89)
String concatenation
+ ; string concatenation operator
"Peanut butter " + "and jelly"
see Facts.java (page. 91)
see Addition.java (page. 92)

5. 2. 1 Character Strings Escape sequences some java escape sequences
see Roses.java (page. 94)
Escape Sequence \b \t \n \r
\" \' \\
Meaning
backspace
tab
newline
carriage return
double quote
single quote
backslash

6. 2. 2 Variables and Assignment
declaration
initialization
see PianoKeys.java (page. 96)
data type
variable name
int total;
int count, temp, result;
int sum = 0;
int base = 32, max = 149;

7. 2. 2 Variables and Assignment
The assignment statement
the assignment operator is the = sign
see Geometry.java (page. 97)
Constants
the final modifier to declare a constant
total = 55;
final int MIN_HEIGHT = 69;

8. 2. 3 Primitive Data Types Integers and floating points Characters
byte(8), short(16), int(32), long(64)
floating point numbers
float(32), double(64)
Characters
a single character
'a' 'X' '7' '$' ',' '\n‘
char topGrade = 'A';
char terminator = ';', separator = ' ';

9. 2. 3 Primitive Data Types Booleans a true or false condition
the reserved word true and false are the only valid values for a boolean type
boolean done = false;

10. 2. 4 Expressions Arithmetic operators Operator precedence operators
see TempConverter.java (page. 108)
Fahrenheit = 9/5 Celsius + 32
Addition +
Subtraction -
Multiplication *
Division /
Remainder %

11. 2. 4 Expressions Increment and decrement operators
the increment operator (++) adds one to its operand
the decrement operator (--) subtracts one from its operand
the statement
count++;
is functionally equivalent to
count = count + 1;
form
++count;

12. 2. 4 Expressions Assignment operators for example, the statement
num += count;
is equivalent to
num = num + count;
operators
Operator += -= *= /= %=
Example
x += y
x -= y
x *= y
x /= y
x %= y
Equivalent To
x = x + y
x = x - y
x = x * y
x = x / y
x = x % y

13. 2. 5 Data Conversion Conversion techniques
data conversions can occur in three ways:
assignment conversion / promotion / casting
assignment conversoin
money is a float variable
dollars is an int variable
money = dollars;
promotion ; happens automatically
sum is a float variable
count is an int variable
result = sum / count;
casting
total and count are int variables
result = (float) total / count;

14. 2. 6 Interactive Programs The Scanner class
input values of various types
some methods of the Scanner class
see Figure 2.7 (page. 115)
see Echo.java (page. 116)
see GasMileage.java (page. 117)

15. 2. 7 Graphics Introduction
focus on graphics and graphical user interfaces
a picture or drawing must be digitized
a picture is made up pixels (picture elements)
picture resolution
the number of pixels used to represent a picture
monitor resolution
the number of pixels that can be displayed by a monitor
digitization
resolution
color depth

16. 2. 7 Graphics Coordinate systems
in a Java program, we can a coordinate system with the origin in the top-left corner
112 Y X
(0, 0) 40
(112, 40)

17. 2. 7 Graphics Representing color The Color class 1-bit black/white
8-bits grayscale
0 ~ 255
24-bits true color (RGB color system)
Red ; 0 ~ 255
Green ; 0 ~ 255
Blue ; 0 ~ 255
The Color class
see Figure 2.10
(page. 121)
Object
Color.black
Color.blue
Color.cyan
Color.orange
Color.white
Color.yellow
RGB Value
0, 0, 0
0, 0, 255
0, 255, 255
255, 200, 0
255, 255, 255
255, 255, 0

18. 2. 8 Applets Introduction Java application Java applet
stand-alone program with a main method
Java applet
a program that is intended to transported over the Web
execute using a web browser
doesn’t have a main method
defines an applet extends the Applet class
use of inheritance
instead, there are several special methods
init / start / stop / destroy methods
paint method
see Einstein.java (page. 123)

19. 2. 8 Applets Executing applets using the Web the HTML applet tag
<head>
<title>The Einstein Applet</title>
</head>
<body>
<applet code="Einstein.class" width=350 height=175>
</applet>
</body>
</html>

20. 2. 9 Drawing Shapes The Graphics class Drawing a line
defined in the java.awt package
a shape can be filled or unfilled
Drawing a line X Y 10
150 20 45
page.drawLine (10, 20, 150, 45);
page.drawLine (150, 45, 10, 20); or

21. 2. 9 Drawing Shapes Drawing a rectangle 50 X 20 40 100 Y
page.drawRect (50, 20, 100, 40);

22. 2. 9 Drawing Shapes Drawing an oval 175 X 20 80 bounding rectangle 50Y
175 20 80
bounding
rectangle 50
page.drawOval (175, 20, 50, 80);

23. 2. 9 Drawing Shapes Drawing shapes background color / foreground color
see Figure 2.12 (page. 126)
see Snowman.java (page. 128)

24. Summary Chapter 2 focused on: character strings primitive data
the declaration and use of variables
expressions and operator precedence
data conversions
accepting input from the user
Java applets
introduction to graphics

25. [ Exercises ] Programming Projects (page. 135)
2. 3 reads two floating point numbers and prints their sum, difference, and product
2. 4 the TempConverter application to convert form Fahrenheit to Celsius
2.12 the Snowman applet modifications
2.18 displays a business card of your own design