csc238 - 2) java programming basics (part 2)

7/30/2019 CSC238 - 2) Java Programming Basics (Part 2)

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CSC238

OBJECT ORIENTED PROGRAMMING

Topic 2 :

Java Programming Basic(Part 2)


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TOPIC COVERED

Character and String

String manipulation

substring

length indexOf

concatenation

Array of primitive

Predefined package Date


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CHARACTER

In Java, single characters are represented usingthe data type char.

Character constants are written as symbolsenclosed in single quotes .

Characters are stored in a computer memory usingsome form of encoding.

ASCII, which stands forAmerican Standard Code

for Information Interchange, is one of the documentcoding schemes widely used today.

Java uses Unicode, which includes ASCII, forrepresenting charconstants.


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CHARACTER

Declaration and

initializationchar ch1, ch2 = X;

Type conversion

between int and

char.

System.out.print("ASCII code ofcharacter X is " + (int) 'X' );

System.out.print("Character withASCII code 88 is " + (char)88 );

This comparison

returns true

because ASCII

value of'A' is 65

while that of'c' is

99.

A < c


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STRING

A stringis a sequence of characters that is

treated as a single value. Instances of the String class are used to

represent strings in Java.

We can access individual characters of a stringby calling the charAt method of the Stringobject.

There are close to 50 methods defined in the

String class. Example: substring, length, andindexOf.

More:http://docs.oracle.com/javase/6/docs/api/java/lan

g/String.html


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STRING

Contains operations to manipulate

strings.

String:

Sequence of zero or more characters.

Enclosed in double quotation marks .

Is processed as a single unit .

Null or empty strings have no characters.

Every character in a string has a relative

position in that string , the first character is in

position 0 .


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STRING

Length of the string is the number ofcharacters in it .

Numeric strings consist of integers or decimal

numbers.

When determining the length of a string ,

blanks count .

Example :

Empty String has length = 0

abc has length = 3 , position of a = 0 ,b= 1 ,

c= 2

a boy has length = 5


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STRING

More examples:

String: The Mentalist

Position of M: ? Position ofsecond e: ? Position of : ?

Length of the String:?


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STRING

String Indexing

The position, or index, of

the first character is 0.


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SUBSTRING

Assume stris a String object and properlyinitialized to a string.

str.substring( i, j ) will return a new string by

extracting characters of str from position i toj-1where 0 i length of str, 0 j length of str,and i j.

If str is programming , then str.substring(3, 7)will create a new string whose value is gram.

The original string strremains unchanged.


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EXAMPLE

String text = Espresso;

text.substring(6,8)

text.substring(0,8)

text.substring(1,5)

text.substring(3,3)

text.substring(4,2)

so

Espresso

spre

error


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LENGTH

Assume str is a String object and properly

initialized to a string.

str.length( ) will return the number of characters

in str.

If str is programming , then str.length( ) will

return 11 because there are 11 characters in it.


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EXAMPLE

String str1, str2, str3, str4;

str1 = Hello ;

str2 = Java ;

str3 = ; //empty string

str4 = ; //one space

str1.length( )

str2.length( )

str3.length( )

str4.length( )

5

4

1

0


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INDEXOF

Assume str and substr are String objects andproperly initialized.

str.indexOf(substr) will return the first position substr

occurs in str.

If stris programming and substris gram , then

str.indexOf(substr) will return 3 because the position

of the first character of substr in str is 3.

If substr does not occur in str, then1 is returned.

The search is case-sensitive.


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EXAMPLE

String str;

str = I Love Java and Java loves me. ;

str.indexOf( J )

str.indexOf( love )

str.indexOf( ove )

str.indexOf( Me )

7

21

-1

3

3 7 21


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CONCATENATION

Assume str1 and str2 are String objects and properlyinitialized.

str1 + str2 will return a new string that is a

concatenation of two strings.

If str1 is pro and str2 is gram , then str1 + str2 will

return program.

Notice that this is an operator and not a method of the

String class. The strings str1 and str2 remains the same.


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EXAMPLE

String str1, str2;

str1 = Jon ;

str2 = Java ;

str1 + str2

str1 + + str2

str2 + , + str1

Are you + str1 + ?

JonJava

Jon Java

Java, Jon

Are you Jon?


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ARRAYSOF PRIMITIVES

Array Declaration

[ ] //variation 1

[] //variation 2

Array Creation

= new [ ]


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ARRAYSOF PRIMITIVES

Example

double[ ] rainfall;

rainfall = new double[12];

Variation 1

double rainfall [];

rainfall = new double[12];

Variation 2


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ACCESSING INDIVIDUAL ELEMENTS

Individual elements in an array accessed with theindexed expression.

double[] rainfall = newdouble[12];

The index of the firstposition in an array is 0.

rainfall 0 1 2 3 4 5 6 7 8 9 10 11

rainfall[2] This indexed expressionrefers to the element at

position #3


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ARRAY PROCESSING SAMPLE1

double[] rainfall = newdouble[12];

double annualAverage,sum = 0.0;

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

rainfall[i] = Double.parseDouble(

JOptionPane.showinputDialog(null,

"Rainfall for month " + (i+1) ));

sum += rainfall[i];

}

annualAverage = sum / rainfall.length;

The public constantlength returns the

capacity of an array.


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ARRAY PROCESSING SAMPLE 2

double[] rainfall = new double[12];

String[] monthName = new String[12];

monthName[0] = "January";

monthName[1] = "February";

double annualAverage, sum = 0.0;

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

rainfall[i] = Double.parseDouble(

JOptionPane.showinputDialog(null,"Rainfall for "

+ monthName[i]));sum += rainfall[i];

}

annualAverage = sum / rainfall.length;

The same pattern for

the remaining ten

months.

The actual month

name instead of a

number.


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ARRAY INITIALIZATION

Like other data types, it is possible to declare

and initialize an array at the same time.

int[] number = { 2, 4, 6, 8 };

double[] samplingData = { 2.443, 8.99, 12.3, 45.009, 18.2,

9.00, 3.123, 22.084, 18.08 };

String[] monthName = {"January", "February", "March",

"April", "May", "June", "July",

"August", "September", "October","November", "December" };

number.length

samplingData.length

monthName.length

4

9

12


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VARIABLE-SIZE DECLARATION

In Java, we are not limited to fixed-size array

declaration.

The following code prompts the user for the size of

an array and declares an array of designated size:

int size;

int[] number;

size=

Integer.parseInt(JOptionPane.showInputDialog(null,

"Size of an array:"));

number = newint[size];


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PREDEFINED-PACKAGE

A package is a JAVA class library a collection of classes andinterfaces in the same directory.

Benefits :-

Package can contain hidden classes that are used by the

package but not visible or accessible outside the package. Classes in a package can have fields and methods that are

visible by all classes within the same package but notoutside.

Different packages can have classes with the same name.Example : java.awt.Frame and java.photo.Frame

To use objects contained in a package, you need to import thepackage the use of keyword impor tat the beginning of theJAVA application. Example : impo rt java.uti l .*;


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PREDEFINED-PACKAGE

java.lang package

Most common Math class methods : pow(x,y),sq rt(x), round (x), PI

Example : AreaCircle = Math.PI * Math.pow(r,2);

java.util package Use of GregorianCalendar class to keep track of time

Specifies data field values such as day, month and year canbe retrieved from GregorianCalendar object by using methodget().

Method get() always returns an integer. Some of the possibleargument are :

DAY_OF_YEAR = returns values from 1 to 366

DAY_OF_MONTH = returns values from 1 to 31

DAY_OF_WEEK = SUNDAY, MONDAY.. SATURDAY ,

YEAR = current year

MONTH = JANUARY, FEBRUARY DECEMBER

HOUR = returns values from 1 to 12 AM or PM


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DATE

The Date class from thejava.util package is

used to represent a date.

When a Date object is created, it is set to

today (the current date set in the computer)

The class has toString method that converts

the internal format to a string.

Date today;today = new Date( );

System.out.println(today.toString( ) );


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SIMPLEDATE FORMAT

The SimpleDateFormat class allows the Date

information to be displayed with various format.

Date today = new Date( );

SimpleDateFormat sdf1, sdf2;

sdf1 = new SimpleDateFormat( MM/dd/yy );

sdf2 = new SimpleDateFormat( MMMM dd, yyyy );

sdf1.format(today);

sdf2.format(today);

System.out.println(sdf1.format(today));

System.out.println(sdf2.format(today));

10/31/03

October 31, 2003


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EXAMPLEOF GREGORIANCALENDAR

CLASSimport java.util.*;

public class AgeCalculator

{

public static void main (String args[])

{

GregorianCalendar Calendar = new GregorianCalendar();Scanner scanner = new Scanner(System.in);

int nowYear;

int birthYear;

int yearsOld;

System.out.println("In what year you were born?");

birthYear = scanner.nextInt();

nowYear = Calendar.get(Calendar.YEAR);

yearsOld = nowYear - birthYear;

System.out.println( "You are " + yearsOld + " years old");

}

}


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USERDEFINED PACKAGE

1. Include a statement packagepackagename; asthe first statement of the source file for the classdefinition.

2. The class declaration must have a visibility modifierpubl ic

3. Create a folder/directory named the same name asyourpackagename. In JAVA, the package musthave a one-to-one correspondence with the folder.

4. Place the classes and interfaces that you want toinclude in the package and compile it.

How to create a package?


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INTRODUCTIONTO JAVA APPLET

An applet

JAVA program that is embedded in a Web page.

Enables Web designers to develop pages that accept input,perform computations and display results.

Enables web designers to create pages that can do anything

a program can do.

Java program that is called from within another application.

Run on a local computer from within another program calledApplet Viewer. To view an applet, it must be called fromwithin another document written in HTML.

Is programmed as a class, like JAVA application where itextends Applet class.

Does not have mainmethod.

Implements paintmethod


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EXAMPLEOF JAVA APPLETS

import java.awt.*;

import javax.swing.*;

public class DisplayQuote extends JApplet

{

public void paint(Graphics g)

{

g.drawString(Anyone who spends their life on a computer is pretty unusual., 20, 30);

}

}

Quotation

Filename : DisplayQuote.java

Filename : Quote.html


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TEST YOURSELF

1. Declare an array of char.

Initialize with value:

p r o g r a m m i n g

2. Declare two Strings withvalue :

i. programming

ii. program

3. Find length char array in

(1) and first String in (2).

4. Find element/value for

chararray[3] and first

String using charAt(3).

5. Substring firstString

with (0,7)6. Compare (5) with

second String.

7. Concatenate second

String and first String.


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END.

Thank you.

csc238 - 2) java programming basics (part 2)

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