Bài giảng Phát triển phần mềm phân tán - Bài 2: Java syntax basics

21-Oct-16

Objectives

LESSON II.

Java syntax basics

•

Understand the Java syntax basics and their

semantics for writing a program.

Vu Thi Huong Giang

SoICT (School of Information and

Communication Technology)

HUST (Hanoi University of Science

and Technology)

Structure of a Java program

Content

•

White space

Separators

Comments

Identifiers and keywords

Data types and literals

Comment line arguments

Program

Package

Book

• Part

•

–

Class

Methods

block

Statement

Expression

Token

–

Chapter

section

Paragraph

Sentence

Phrase

Word

•

–

»

•

I. White spaces

II. Separators

•

A whitespace is a space, a tab or a new line.

It is used to separate the tokens in a source file

and to improve readability

• Help define the structure of program

()

parenthesis

braces

lists of parameters in method definitions and calls,

precedence in expressions,

type casts

•

Java don’t require indentation rules

{}

block of code, local scope,

class definitions, method definitions,

automatically initialized arrays

–

Example: following codes are equivalent

[]

;

brackets

semicolon

comma

declaring array types,

referring to array values brackets

package firstpackage;

public class SayHello

public static void main(String[] args)

// Display Chao! on the screen

System.out.println ("Chao!");

}

{

terminating statements,

chain statements inside the “for” statement

,

separating multiple identifiers in a variable declaration,

chains statements in the test,

expression of a for loop

}

.

period (dot)

colon

separate package names from sub packages and classes,

separating an object variable from its attribute or method

package firstpackage; public class SayHello {public static

void main(String[] args) // Display Chao! on the screen

System.out.println ("Chao!");}}

{

:

using after loop labels

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III. Comment

Comments

•

Example

Implementation comment:

•

Comments are used to

/** SayHello aims to display

a

hello in

Vietnamese on the standard output

device.

•

/* text */

Ignore the text between /*

and */

// text

–

give overviews of code

*

–

*

–

provide additional information that is not readily

available in the code itself

*/

class SayHello

{

•

/* The program starts here.*/

•

Comments should contain only information that is

relevant to reading and understanding the

program.

–

Ignore all text from //to the

end of the line

public static void main(String[] args)

{

// Display Chao! on the screen

System.out.println(“Chao!");

Documentation comment:

/** documentation */

}

•

Two kinds of comments:

}

–

javadoc uses it to

–

Implementation comment

automatically generate

software documentation

–

Documentation comment

javadoc tool

•

Used to automatically generate the API

documentation or the implementation documentation

for a set of Java source files.

IV. IDENTIFIERS AND

KEYWORDS

–

Parse the declarations and documentation comments

–

Produce a corresponding set of HTML pages describing

classes, interfaces, constructors, methods, and fields

•

Frequent tags of javadoc:

@param : Explanation of argument name

–

@return : Explanation of the return value of the method of

the object is described

–

@exception class-name description : Explanation of the

exception class-name that may be thrown by the method

@see reference : Adds a "See Also" heading with a link or

text entry that points to reference

1. Identifier

2. Naming rules

3. Keywords

1. Identifier

2. Naming Rules

•

Class: starts with upper case

•

Java identifiers are tokens that represent names of

variables, constants, methods, objects, classes, files written

in Java language

camel style (capitalize the first letter of each

subsequent word)

– ThisIsAnExampleOfClassName, Circle, Account, ..

•

Features:

–

Case-sensitive

•

Method and variable: start with low case; camel style

•

identifier Hello <> identifier hello <> identifier HELLO

– thisIsAnExampleOfMethodName, setColor, isFull, ..

–

No limit of length

Not the same as Java keywords like class, public, void, etc.

Not be true, false or null

Basic data type constant : all capitals

– MAX_LENGTH, TAX_VALUE ..

Object constant: all low cases

– Color.red, System.out ..

•

Structure: Identifiers must begin with either a letter, an

underscore “_” or a dollar sign “$”.

–

 Choose meaning and descriptive names

 Consistent naming in the whole program

Letters: lower or upper case

Subsequent characters: letters, digital numbers, etc.

–

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3. Java keywords

•

Keywords are predefined identifiers reserved by Java for a

specific purpose.

53 Java reserved words:

V. DATA TYPES AND

LITERALS

abstract continue

float

for

goto

if

native

new

null

strictfp

super

switch

synchronized

this

void

volatile

while

assert

boolean

break

byte

default

do

double

else

package

1. Data type categories

a. Primitive data types

b. Reference data types

c. Literals

implements private

case

enum

import

protected throw

catch

char

class

const

extends

false

final

finally

instanceof public

throws

transient

true

int

interface

long

return

short

static

try

2. Variables

3. Type compatibility

4. Strong typing

5. Array



You cannot use reserved words as names for your

variables, classes, methods, etc.

13

1. Data type categories

8 primitive data types

Type

byte

short

int

Size

Min value

-128

Max value

127

Default

•

Primitive data types : 8

Reference data types: 2

Literals: 6

Integer

8 bits

0

16 bits

32 bits

64 bits

32 bits

-32768

32767

0

-2,147,483,648

-9 x 10¹⁸

2,147,483,647

9 x 10¹⁸

0

long

float

0

-3.4 x 10³⁸

with 7

significant digits digits

-1.7 x 10³⁰⁸

with 15

3.4 x 10³⁸

with 7 significant

0.0

Floating

point

number

double

64 bits

1.7 x 10³⁰⁸

with 15

0.0

significant digits significant digits

char

16 bits

\u0000 (0)

false

\uffff (65636)

true

\u0000

false

Unicode

character

boolean 1 bits

Boolean

values

Composite data types

(reference types)

Literals

•

Literals are constant value of 6 following types:

•

Composite data type: constructed out of primitive

data types and other composite date types.

–

Integer literals

•

Decimal: 100 or 100L (long type)

Octal: 013 or 013L

Hexadecimal: 0x52 or 0xFFl

–

Object: value of every type

–

Array: ordered list of values of the same data type

•

Data of composite types don’t have well-defined

standard size, so they are handled by reference.

The default value of this type is null (no data

should be referenced).

–

Floating-point literals (default is double type)

•

Decimal expression:

0.23445, 0.655d (double type) or 0.23445F (float type)

Exponent (scientific) expression: 6.02E13

–

•

–

Boolean literals: true or false

Character literals: ‘a’, ‘\t’, ‘\u3042’

String literals: “Hello”, “Have a nice day!”

Null literal: null(there no data should be referenced)

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2. Variables

Assignment and initialization

•

Assignment: associate a

value to a variable

•

A variable is a name

that refers to a value

located in memory

 Used to store data

int myFirstNumber, mySecondNumber;

myFirstNumber

=

100;

myFirstNumber*2;

mySecondNumber

=

variable

= <expression>;

•

Declaration:

int myFirstNumber;

int mySecondNumber;

–

variable's name

•

Initialization: give an initial

value in the declaration

–

the type of information

that it will hold (data

type)

or

int myThirdNumber

int myFourthNumber

= 10;

–

Static: initialize with a literal

int myFirstNumber, mySecondNumber;

Multiple variables of the

same type can be

created in one

–

Dynamic: initialize with an

expression available at the

moment

=

myThirdNumber

+ 5;

declaration

20

Primitive variable

Reference variable

•

Reference: the memory address at which a composite data

(object or array) is stored.

Reference variable:

•

A primitive variable is a variable of one of

primitive data types

A primitive variable stores the data in the actual

memory location where it is

int myFirstNumber;

–

Store the address in the memory location

Point to another memory location where the actual data is

When a variable is referenced in a program, its current value is used

myFirstNumber

=

100;

•

Example:

String firstName

= « Giang »;

Memory address: 1001

Memory address: 1500

Memory address: 2000

3. Type compatibility

Type casting

•

Integer types and floating-point types are compatible with

each other

Implicit type casting

Explicit type casting

•

Numeric types are not compatible with char or boolean

char and booleanare not compatible with each other

What happens if a value of type T1 is assigned to a variable

of another type T2 ?

T1 t1;

•

When operating on values

of different data types, the

lower one is promoted to

the type of the higher one.

•

The type is put in

parentheses in front of the

value being converted.

Example: if we want a

floating-point result of the

division, we can cast the

variable total:

•

Example:

T2 t2 = t1;

int intVal = 123;

–

types T1 and T2 are incompatible  not possible

types T1 and T2 are compatible:

• T1 and T2are the same

long longVal = 213000L;

int count, total;

float result;

longVal

intVal

=

intVal; //ok

longVal; //na

• T1 is larger than T2

• T2 is larger than T1

 type casting

=

result

=

(float) total / count;

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4. Strong typing

5. Array

•

Every variable and expression has a type

•

Array: ordered list of elements which hold values

of the same data type

Declaration:

–

All assignments are checked for type-compatibility

Every type is strictly defined

data_type[] array_name;

–

No automatic conversion of non-compatible, conflicting

types

data_type array_name[];

•

Java compiler checks the type of all expressions

and parameters

•

Creation:

data_type[] array_name = new data_type[SIZE];

–

Any typing errors must be corrected for a successful

data_type array_name[] = new data_type[SIZE];

compilation

Initialization:

data_type[] array_name = {value1, value2,.., valuen};

data_type array_name[] = {value1, value2,.., valuen};

Example

Array of reference type

char c[] = new char[5];

//creation

•

Be aware that the array of the reference type is

"array of the variables that refer to the objects",

and that it is not "array of the objects".

//initialization all at once

char d[] {‘A’,’B’,‘1’,‘2’,‘3’};

=

char e[] = new char [3]; // creation

//assignment for each element

String array[] = new String[5];

e[0]

=

‘0’; e[1]

=

‘A’; e[2]

=

‘X’; e[3]

=

‘3’; e[4] = ‘3’;

array[0] = “Chao”;

c

d

e

0

1

2

3

4

\u0000

0

1

2

3

4

‘A’

0

1

2

3

4

‘0’

\u0000

‘B’

‘1’

‘2’

‘3’

‘A’

‘X’

‘3’

\u0000

index

value

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Multi-dimensional array

VI. Comment line arguments

•

Multidimensional arrays are implemented as arrays of

arrays.

•

When a java application is launched, the runtime

system starts by calling the main()method of its main

class

•

Example

•

The main()method then calls all methods found in his

body to run this application

Syntax:

// integer array 512 x 128 elements

int[][] twoD = new int[512][128];

// character array

char[][][] threeD

// String array

String[][] dogs

8

=

x 16

new char[8][16][24];

rows x columns

{{ "terry", "brown" },

x 24

public static void main(String args[]){

4

=

2

// body

}

{

"Kristin", "white" }

"toby", "gray"},

"fido", "black"}

–

The runtime system passes arguments to the application

through an array of Strings.

•

Arguments can be passed from the command line

};

•

Any number of arguments can be accepted as configuration

information of the application.

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Comment line arguments

Example

public class Echo {

public static void main (String[] args) {

•

Launching a java application without

configuration information

for (String s: args) { System.out.println(s); }

}

prompt> java class_name

>java Echo I got it

•

Launching a java application with configuration

information

public class MyFavouriteBook {

public static void main(String[] args) {

System.out.println("My favourite book");

System.out.println("Title: " + args[0]);

System.out.println("Author: " + args[1]);

System.out.println("Language: " + args[2]);

System.out.println(

prompt> java class_name arg[0] arg[1] .. arg[n]

"Why do I love it ?" + args[3]);

}

> java MyFavouriteBook A B C D

Quiz: Javadoc

Quiz 1+2 - Solution

1. Explain the result

javadoc –private Circle.java

Show all class and member

Given a Java source file named

virtual_parse_stack.java

javadoc -author -version Circle.java

Include the tags @author and @version

This file can be found at JDK installation folder

C:\Program Files\Java\jdk1.7.0_03\src.zip

\com\sun\java_cup\internal\runtime

1. Run the following command for producing different

documentations.

javadoc –private virtual_parse_stack.java

javadoc -author -version virtual_parse_stack.java

2. Explain the obtained results

3. Try to get the same results by using Eclipse.

Quiz 3 - Solution

Quiz: array

4. Given a one dimension array of int type, write a

program named OneDimensionArrayUsage that

calculates its sum total (int) and its mean value

(float)

int data[] =

{1, 80,22, 134, 0, 33, 93,45,33, 12} ;

•

The expected output is

sum: 453

mean: 45.3

5. Extend the program so that it displays the

minimal and maximal value of the array.

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Quiz 3 - Solution

Quiz 4 - Solution

public class Arithmetic

{

public class OneDimensionArrayUsage

{

public static void main(String[] args)

//...

{

public static void main(String[] args)

int data[] {1, 80,22, 134, 0, 33, 93,45,33, 12};

int sum 0; // Total sum

{

=

int min

= 0; int max = 0;

=

for(int i=0; i<data.length; i++){

// Calculation of total

sum += data[i];

for(int i=0; i<data.length; i++){

// Calculation of total

sum += data[i];

}

if (data[i]

}

<

>

min) min

max) max

=

data[i];

float mean

= sum / 10.0f; // Mean

//...

System.out.println(“Total sum :" + sum);

System.out.println("Minimal value :"

+

min);

max);

System.out.println(“Mean :" + mean);

System.out.println("Maximal value :"

}

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Review

•

White space: separate the tokens

Separators: help define the structure of program

Comment: improve readability + auto generate

documentation

•

Identifier: naming

Data types: every variable, literal and expression

has a type

•

Comment line arguments: pass arguments to the

application through an array of Strings.

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Bài giảng Phát triển phần mềm phân tán - Bài 2: Java syntax basics - Vũ Thị Hương Giang