1. An overview of Java, Data types and variables
Lecture 4 from (Chapters 2 and 3)
2018/11/28

2. Elements of Java – lexical values, chapter 2 (pages 37-39)
White spaces: Java is a free-form language. There is no special rue for us to follow.
Identifiers: Identifiers are used for class names, method names and variables names. They must not begin with a number.
The following is correct: height, a2, $sign
The following is incorrect: 2dco, yes/no
Literals: A constant value is created by using literal such as 200 (integer), 12.3 (floating-point value), “DCO” (string)
2018/11/282018/11/28

3. Elements of Java – lexical values
Comments: // (single line) /*…… */ (block) /**….. */ (documentation for HTML format
Separators: separators are used to terminate statements
() parentheses
{} braces
[] brackets
; semicolon
, comma
. Period
2018/11/282018/11/28

4. Java Keywords – there are 49 words
abstract
finally
public
assert3
float
return
boolean
for
short
break
goto1
static
byte if
strictfp2
case
implements
super
catch
import
switch
char
instanceof
synchronized
class
int
this
const1
interface
throw
continue
long
throws
default
native
transient do
new
try
double
package
void
else
private
volatile
extends
protected
while
final
It means that
you cannot
use it as
a variable
2018/11/282018/11/28

5. Java Class
The first program in last lecture you used print() and println() are from System class.
There are several built-in class libraries that supports I/O, string handling, networking and graphics.
2018/11/282018/11/28

6. Data Types and Variables, chapter 3
Integers
Floating point
Characters
Booleans
Variables
Type conversion (integer to floating)
2018/11/282018/11/28

7. Integers – 4 types Name Size (bits) Range byte 8 -128 to 127
short to 32767
int to
long to
2018/11/282018/11/28

8. Example of byte, short, int and long
result
2018/11/282018/11/28

9. Example – out of range, (byte)
year > 127
2018/11/282018/11/28

10. Floating – 2 types Type size (bits) range
Double exp(-324) to 1.8 exp(308)
float exp(-45) to 3.4 exp(38)
2018/11/282018/11/28

11. Example – long
result
2018/11/282018/11/28

12. Example – out of range
> 3.4e38
2018/11/282018/11/28

13. Characters Java uses two bytes to store characters (0 to 65536)
The standard of ASCII ranges from 0 to 127
For example, X in ASCII is 88
2018/11/282018/11/28

14. ASCII Table – in hexadecimal (16)
2018/11/282018/11/28

15. Example – character
result
2018/11/282018/11/28

16. Character.isLetter(ch) – return true or false
2018/11/282018/11/28

17. Character.isDigit(ch) – return true or false
white space includes 0020,
0009, 000A, 000B and 000D
2018/11/282018/11/28

18. Booleans Java has a simple type called boolean.
It has two values, true or false
For example, a = 4, b = 5, (a >b) is true
For example, (4 = 4) is true
For example, (3 > 4) is false
2018/11/282018/11/28

19. Example of boolean
2018/11/282018/11/28

20. Escape sequence
Escape sequence uses “\u” to stand for white space. They are 16-bit values.
Sequence name value
\n newline \u000A
\t tab \u0009
\b backspace \u0008
\r carriage return \u000D
\f form feed \u000C
\’ single quote
2018/11/282018/11/28

21. String Strings literals are similar to English. Examples are:
“hello how are you?”
“three \blines”
“\” This statement is quoted \””
2018/11/282018/11/28

22. Example of String and Escape Sequence
newline
2018/11/282018/11/28

23. Variables In java, variables are basic storage. The basic format is
type identifier [= value], identifier [= value];
Examples are:
int a =10, b = 20, c=30;
int a, b, c;
double a = 2.3, b = 4.5, d= 6.7;
char x = ‘z’;
2018/11/282018/11/28

24. Type conversion
Byte defines the value between -127 to 128. If you assign a value that is larger than 128, you have to use short or integer. This needs conversion.
2018/11/282018/11/28

25. Example
type conversion
overflow
2018/11/282018/11/28

26. Example
type conversion
truncated
2018/11/282018/11/28

27. Summary Integers – 4 types, byte, short, int and long
Floating point – 2 types, float and double
Characters – ASCII, ‘X’
Booleans – true or false
String – “How are you?”
Variables – u67 (correct), 67u (incorrect)
Type conversion (integer to floating)
2018/11/282018/11/28