1. Introduction to Computing Using Java
Java Language Basics a
Michael Fung, CS&E, The Chinese University of HK

2. Common Syntax/ Grammar Notations
Arrow-bracketed item
<someName> or <someName>
Fill in this blank WITHOUT the arrows
This is a place-holder
DO NOT type the arrows in actual code!
Brackets and punctuations
{ } ( ) [ ] , ; .
Type carefully and place in appropriate location a
Michael Fung, CS&E, The Chinese University of HK

3. Michael Fung, CS&E, The Chinese University of HK
Quotes and Brackets
' Single Quote 單弔引號
" Double Quote 雙引號
( ) Brackets/ Parentheses 括號/ 小括號
[ ] Square Brackets 方括號/ 中括號
{ } Curly Brackets/ Braces 花括號/ 大括號
; Semi-colon 分號
. Dot/ Full-stop 點
, Comma 逗號 a
Michael Fung, CS&E, The Chinese University of HK

4. Java Naming Convention (Capitalization)
Examples
keyword
class, if, double, int, for, while
packagename
javax.swing, javaapplication12
ClassName
String, JOptionPane, Double
FileName
HelloWorld.java, JOptionPane.class
methodName()
showMessageDialog( ), parseInt( )
fieldName
System.out, DrinkDispenser.cokeStock
variableName
numberOfStudents, bodyWeight
CONSTANT
JFrame.HEIGHT, Math.PI a
Michael Fung, CS&E, The Chinese University of HK

5. Java Program Structure
import <packagename>.<someclassname>;
import <packagename>.*;
class <ClassName> {
<type> <fieldName1>;
<type> <fieldName2>;
<type> <methodName1> ( ... ) }
<type> <methodName2> ( ... )
Field (Data Member)
Declarations
Method Declarations a
Michael Fung, CS&E, The Chinese University of HK

6. Michael Fung, CS&E, The Chinese University of HK
Java Program Example
import java.util.Vector;
import javax.swing.*;
class CurrencyConverter {
double rateHKtoEuro = ;
double rateHKtoUS = 0.128;
double convertEuro2US ( double amountEuro )
{ // details skipped }
double convertUS2HK ( double amountUS )
Field (Data Member)
Declarations
Method Declarations a
Michael Fung, CS&E, The Chinese University of HK

7. Michael Fung, CS&E, The Chinese University of HK
Data Item Declaration
Data items are used to store data.
Such as fields, local variables, constants, …
We give name (an identifier) to each data item.
e.g.
“Ma Liu Shui, Tai Po Road, Shatin.” is a piece of data.
This information is called CUHKaddress.
Each data item must bear a type.
CUHKaddress is of type String (text). a
Michael Fung, CS&E, The Chinese University of HK

8. Michael Fung, CS&E, The Chinese University of HK
Identifier
Names introduced by programmers in computer languages are called identifiers.
e.g.
Address
hello_World
One2Free
j_u_s_t___2___say___hi
Ring a
Michael Fung, CS&E, The Chinese University of HK

9. Michael Fung, CS&E, The Chinese University of HK
Java Identifiers
Valid components
ABCDEFGHIJKLMNOPQRSTUVWXYZ
abcdefghijklmnopqrstuvwxyz
_ “underscore”
Space is disallowed.
Must start with a letter or underscore.
e.g. 12Free is disallowed while One2Free is okay
Case sensitive.
e.g. Hello is not equal to hello nor HellO a
Michael Fung, CS&E, The Chinese University of HK

10. Michael Fung, CS&E, The Chinese University of HK
Choice of Identifiers
Easy to understand and remember.
e.g. noOfEnquiries, Trees, timeToLive, name, address, count, isOK, List, experiment12
May use multiple words (without space!).
e.g. grade_point_average, myBirthday, numberOfStudents
Don’t be lazy!
e.g. i, j, k, a, b, c, d, e, … a
Michael Fung, CS&E, The Chinese University of HK

11. Michael Fung, CS&E, The Chinese University of HK
What Kind Is It?
Given you an identifier noOfStudents in my Java program, do you (most importantly, the computer or the compiler) know what it is?
It may be:
a class name
a method name
a field name (could be variable or constant)
a local variable name (data item declared in a method) a
Michael Fung, CS&E, The Chinese University of HK

12. Michael Fung, CS&E, The Chinese University of HK
What Kind Is It?
It all depends on where we put it in our program.
Let’s now consider the third case, field name.
When an identifier appears in a data item declaration within a class BUT not in a method, it is a field name.
e.g.
class XYZ {
int noOfStudents;
JFrame frame;
double GPA, termGPA; } a
Michael Fung, CS&E, The Chinese University of HK

13. Michael Fung, CS&E, The Chinese University of HK
What Kind Is It?
It all depends on where we put it in our program.
When an identifier appears in a data item declaration within a method, it is a local variable.
e.g.
class XYZ {
public static void main(String[] args) {
int noOfStudents;
JFrame frame;
double GPA, termGPA; } a
Michael Fung, CS&E, The Chinese University of HK

14. Declaration of a Field/ Local Variable
“Type” refers to both primitive type or class.
In general, four basic forms of declarations:
<type name> identifier;
<type name> identifier1, identifier2, … ;
<type name> identifier = <initial value>;
<type name> identifier1 = <initial value1>, identifier2 = <initial value2>, …;
Examples of the last two forms:
String myName = "Michael Fung";
double HangSengIndex = , rainfall = 3.4; a
Michael Fung, CS&E, The Chinese University of HK

15. Michael Fung, CS&E, The Chinese University of HK
What is Type?
A type restricts the kind and range of values a data item or an expression could take.
e.g. Sex  [‘M’, ‘F’]
HKID  K123456(7)
Type must be matched (各從其類)
e.g. String name = "Chan Tai Man";
String myName = 123;
// 123 is a number, neither text nor String
// "123" however, is a String   a
Michael Fung, CS&E, The Chinese University of HK

16. What are Primitive Types?
Eight build-in (primitive) types in Java:
byte for storing a 8-bit signed integer
short for storing a 16-bit signed integer
int for storing a 32-bit signed integer
long for storing a 64-bit signed integer
float for storing a 32-bit real number
double for storing a 64-bit real number
char for storing a single character
boolean for storing a true/false (logic) value a
Michael Fung, CS&E, The Chinese University of HK

17. What are Primitive Types?
Eight build-in (primitive) types in Java:
byte [-128  127]
short [  32767]
int [  ]
long [  ]
float [±1038 with floating point]
double [±10308 with floating point]
char [‘A’, ‘B’, …, ‘a’, ‘b’, …, ‘0’, ‘1’, …, ‘!’, ‘#’]
boolean [true, false] a
Michael Fung, CS&E, The Chinese University of HK

18. Michael Fung, CS&E, The Chinese University of HK
Use of Primitive Types
To store a number
double pi = ;
To store an age of 108
byte age = 108;
To find and keep the reciprocal of 1997
double answer = 1.0 / 1997; a
Michael Fung, CS&E, The Chinese University of HK

19. Assignment Statement/ Expression
To store a value into a data storage on the left-hand-side.
e.g.
int temperature, oldWeight, newWeight;
double GPA;
temperature = 24;
oldWeight = 110;
newWeight = oldWeight – 5;
GPA = 4.0;
GPA = 3; a
Michael Fung, CS&E, The Chinese University of HK

20. Assignment Statement/ Expression
A field or local variable ‘takes the value of’ (‘becomes’) something.
The effect is instantaneous and lasting onwards, but not back-dated.
Type MUST be matched.
e.g. birds and elephants are different
Implicit coercion (type conversion) may be done by the compiler.
e.g. for numeric types (see example later) a
Michael Fung, CS&E, The Chinese University of HK

21. Michael Fung, CS&E, The Chinese University of HK
Expression
Examples:
(-5)
(1.234 / 56 + Pi) * 9.8
m * c * c
USdollar * 7.80
Use with assignment operator:
HKdollar = USdollar * 7.80; a
Michael Fung, CS&E, The Chinese University of HK

22. Michael Fung, CS&E, The Chinese University of HK
7-Minute Break a
Michael Fung, CS&E, The Chinese University of HK

23. Michael Fung, CS&E, The Chinese University of HK
Thomas Cook
class UStoHKConverter {
static final double rate = 7.80;
public static void main (String [ ] args) {
double USdollar = ;
double HKdollar = USdollar * rate;
System.out.println(
"US" + USdollar + " -> HK" + HKdollar); }
rate 
7.80 a
Michael Fung, CS&E, The Chinese University of HK

24. Thomas Cook Modifiers/ Adjectives to be discussed later
class UStoHKConverter {
static final double rate = 7.80;
public static void main (String [ ] args) {
double USdollar = ;
double HKdollar = USdollar * rate;
System.out.println(
"US" + USdollar + " -> HK" + HKdollar); }
rate 
7.80
Modifiers/ Adjectives to be discussed later
A class (static) constant (final) a
Michael Fung, CS&E, The Chinese University of HK

25. Thomas Cook A field declaration with initialization and some modifiers
class UStoHKConverter {
static final double rate = 7.80;
public static void main (String [ ] args) {
double USdollar = ;
double HKdollar = USdollar * rate;
System.out.println(
"US" + USdollar + " -> HK" + HKdollar); }
rate 
7.80
A field declaration with initialization and some modifiers a
Michael Fung, CS&E, The Chinese University of HK

26. Thomas Cook A local variable declaration with initialization
class UStoHKConverter {
static final double rate = 7.80;
public static void main (String [ ] args) {
double USdollar = ;
double HKdollar = USdollar * rate;
System.out.println(
"US" + USdollar + " -> HK" + HKdollar); }
rate 
7.80
A local variable declaration with initialization a
Michael Fung, CS&E, The Chinese University of HK

27. Michael Fung, CS&E, The Chinese University of HK
Thomas Cook
class UStoHKConverter {
static final double rate = 7.80;
public static void main (String [ ] args) {
double USdollar = ;
double HKdollar = USdollar * rate;
System.out.println(
"US" + USdollar + " -> HK" + HKdollar); }
rate 
7.80
An expression a
Michael Fung, CS&E, The Chinese University of HK

28. Thomas Cook Another local variable declaration with initialization
class UStoHKConverter {
static final double rate = 7.80;
public static void main (String [ ] args) {
double USdollar = ;
double HKdollar = USdollar * rate;
System.out.println(
"US" + USdollar + " -> HK" + HKdollar); }
rate 
7.80
Another local variable declaration with initialization a
Michael Fung, CS&E, The Chinese University of HK

29. Michael Fung, CS&E, The Chinese University of HK
Thomas Cook
class UStoHKConverter {
static final double rate = 7.80;
public static void main (String [ ] args) {
double USdollar = ;
double HKdollar = USdollar * rate;
System.out.println(
"US" + USdollar + " -> HK" + HKdollar); }
rate 
7.80
Print the result a
Michael Fung, CS&E, The Chinese University of HK

30. Michael Fung, CS&E, The Chinese University of HK
Thomas Cook
class UStoHKConverter {
static final double rate = 7.80;
public static void main (String [ ] args) {
double USdollar = ;
double HKdollar = USdollar * rate;
System.out.println(
"US" + USdollar + " -> HK" + HKdollar); }
rate 
7.80
Strings
Strings a
Michael Fung, CS&E, The Chinese University of HK

31. Michael Fung, CS&E, The Chinese University of HK
Result
US > HK962.91 a
Michael Fung, CS&E, The Chinese University of HK

32. Michael Fung, CS&E, The Chinese University of HK
Type in Expression
Type promotion/conversion
byte  short  int  long  float  double
byte b = 104;
float f = (float) ;
double d = 35 * f – 29.7 / b;
double a
Michael Fung, CS&E, The Chinese University of HK

33. Michael Fung, CS&E, The Chinese University of HK
Type in Expression
Type promotion/conversion
byte  short  int  long  float  double
byte b = 104;
float f = (float) ;
double d = 35 * f – 29.7 / b;
[double  int * float – double / byte] a
Michael Fung, CS&E, The Chinese University of HK

34. Michael Fung, CS&E, The Chinese University of HK
Type in Expression
Type promotion/conversion
byte  short  int  long  float  double
byte b = 104;
float f = (float) ;
double d = 35 * f – 29.7 / b;
[double  float * float – double / double] a
Michael Fung, CS&E, The Chinese University of HK

35. Michael Fung, CS&E, The Chinese University of HK
Type in Expression
Type promotion/conversion
byte  short  int  long  float  double
byte b = 104;
float f = (float) ;
double d = 35 * f – 29.7 / b;
[double  float – double] a
Michael Fung, CS&E, The Chinese University of HK

36. Michael Fung, CS&E, The Chinese University of HK
Type in Expression
Type promotion/conversion
byte  short  int  long  float  double
byte b = 104;
float f = (float) ;
double d = 35 * f – 29.7 / b;
[double  double – double] a
Michael Fung, CS&E, The Chinese University of HK

37. Michael Fung, CS&E, The Chinese University of HK
Type in Expression
Type promotion/conversion
byte  short  int  long  float  double
byte b = 104;
float f = (float) ;
double d = 35 * f – 29.7 / b;
[double  double] a
Michael Fung, CS&E, The Chinese University of HK

38. Michael Fung, CS&E, The Chinese University of HK
Default Type
Integer literals (integer numbers appearing in program code) are generally treated as int type.
e.g. i = 7 * j / (-9 + k);
e.g. Math.cos(30 * Math.PI / 180);
Real number/ floating point number literals (numbers with decimal point or in exponential notation appearing in program code) are generally treated as double type.
e.g. p = 7.0 * q ;
e.g. Math.toRadians(3e-1 * 100.);
3.0 x 10-1 a
Michael Fung, CS&E, The Chinese University of HK

39. Michael Fung, CS&E, The Chinese University of HK
Summary
Common conventions and nomenclature
Java program structure
Data item declaration
type and identifier
field VS local variable a
Michael Fung, CS&E, The Chinese University of HK

40. Michael Fung, CS&E, The Chinese University of HK
Summary
Type in Java
8 primitive types
class types (to be discusses later)
Assignment statement and Expressions a
Michael Fung, CS&E, The Chinese University of HK

41. Michael Fung, CS&E, The Chinese University of HK
End Note
Readings and References
Section 2.1 – 2.5
Exercise
1.3, 1.4, 1.16, 1.17, 1.18,
2.2, 2.3, 2.4, 2.5, 2.6, 2.7
Programming Projects
2.1 a
Michael Fung, CS&E, The Chinese University of HK