20090720100749mts 2023 Chp 3 Edited

MTS 2023 Object Oriented Programming Basic of Java

1

The brief History of JAVA 

Around 1990 James Gosling , Bill Joy and others at Sun Microsystems developing a language called Oak.



Oak needed to be:   

Platform independent Extremely reliable Compact.

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As of 1993, interactive TV and PDA failed, Internet and Web explosion began. JAVA emergence.



By 1994 Sun's HotJava browser appeared. Power of applets

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Learn more in : http://www.javarss.com/java-timeline-10years.html

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What is JAVA? 

A high level language - the Java language is a high level one that at a glance looks very similar to C and C++ but offers many unique features of its own.



Java bytecode - a compiler, such as Sun's javac, transforms the Java language source code to bytecode that runs in the JVM.

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Java Virtual Machine (JVM) - a program, such as Sun's java, that runs on a given platform and takes the bytecode programs as input and interprets them just as if it were a physical processor executing machine code

3

Some of JAVA features 

Platform Independence 



Object Oriented 





Object oriented throughout - no coding outside of class definitions, including main( ). An extensive class library available in the core language packages.

Compiler/Interpreter Combo 



The Write-Once-Run-Anywhere

Code is compiled to bytecodes that are interpreted by a Java virtual machines (JVM) .

Robust 

Exception handling built-in, strong type checking), local variables must be initialized. 4

JAVA vs C++ Number of significant differences, the most significant of which include: Data Types References vs. Pointers Automatic Variables Boolean Expressions: 5

Coding using JAVA.. what do u need?    

JSDK IDE Computer..  Reference books…

6

JSDK? 

2 Java SE family:  





Java SE Development Kit (JDK) Java SE Runtime Environment (JRE).

The JRE provides the Java APIs, Java Virtual Machine (HotSpot VM), and other components necessary to run applets and applications The JDK = JRE, plus compilers and debuggers necessary for developing applets and applications.

7

The First Java Program 

The fundamental OOP concept illustrated by the program: An object-oriented program uses objects.



This program displays a window on the screen. The size of the window is set to 300 pixels wide and 200 pixels high. Its title is set to My First Java Program.



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Program Ch2Sample1 import javax.swing.*; class Sample { public static void main(String[ ] args) { JFrame

myWindow;

myWindow = new JFrame( );

Declare a name Create an object

myWindow.setSize(300, 200); myWindow.setTitle(“My First Java Program”); myWindow.setVisible(true); } } Use an object

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Program Diagram for Ch2Sample1

Sample

setSize(300, 200 ) setTitle(“My First Java Program”)

(true) setVisible

myWindow : JFrame

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Dependency Relationship

Sample myWindow : JFrame

Instead of drawing all messages, we summarize it by showing only the dependency relationship. The diagram shows that Sample “depends” on the service provided by myWindow.

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Object Declaration Class Name This class must be defined before this declaration can be stated.

Object Name One object is declared here.

JFrame

myWindow;

More Examples

Account Student Vehicle

customer; jan, jim, jon; car1, car2;

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Object Creation Class Name An instance of this class is created.

Object Name Name of the object we are creating here.

myWindow

More Examples

= new JFrame (

Argument No arguments are used here.

);

customer = new Customer( ); jon = new Student(“John Java”); car1 = new Vehicle( );

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Sending a Message Object Name Name of the object to which we are sending a message.

Method Name The name of the message we are sending.

myWindow

More Examples

.

setVisible

(

Argument The argument we are passing with the message.

true

) ;

account.deposit( 200.0 ); student.setName(“john”); car1.startEngine( );

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Program Components 

A Java program is composed of 

comments,



import statements, and



class declarations.

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Program Component: Comment /*

Chapter 2 Sample Program: Displaying a Window File: Ch2Sample2.java */ import javax.swing.*; class Ch2Sample1 { public static void main(String[ ] args) { JFrame

myWindow;

Comment

myWindow = new JFrame( ); myWindow.setSize(300, 200); myWindow.setTitle(“My First Java Program”); myWindow.setVisible(true); } }

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Matching Comment Markers /* This is a comment on one line */

/* Comment number 1 */ /* Comment number 2 */

These are part of the comment.

/*

/* /* This is a comment */

Error: No matching beginning marker.

*/ 17

Import Statement /* Chapter 2 Sample Program: Displaying a Window File: Ch2Sample2.java */ import javax.swing.*;

Import Statement

class Ch2Sample1 { public static void main(String[ ] args) { JFrame

myWindow;

myWindow = new JFrame( ); myWindow.setSize(300, 200); myWindow.setTitle(“My First Java Program”); myWindow.setVisible(true); } }

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Import Statement Syntax and Semantics Class Name Package Name The name of the class we want to import. Use asterisks to import all classes.

Name of the package that contains the classes we want to use.

.

<package name> ; e.g.

More Examples

dorm import import import

.



Resident;

javax.swing.JFrame; java.util.*; com.drcaffeine.simplegui.*;

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Class Declaration /* Chapter 2 Sample Program: Displaying a Window

Class Declaration

File: Ch2Sample2.java */ import javax.swing.*; class Ch2Sample1 { public static void main(String[ ] args) { JFrame

myWindow;

myWindow = new JFrame( ); myWindow.setSize(300, 200); myWindow.setTitle(“My First Java Program”); myWindow.setVisible(true); } }

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Method Declaration /* Chapter 2 Sample Program: Displaying a Window File: Ch2Sample2.java */

Method Declaration

import javax.swing.*; class Ch2Sample1 { public static void main(String[ ] args) { JFrame

myWindow;

myWindow = new JFrame( ); myWindow.setSize(300, 200); myWindow.setTitle(“My First Java Program”); myWindow.setVisible(true); } }

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Method Declaration Elements Modifier

public

Modifier

static

Return Type

void

JFrame myWindow;

Method Name

main(

Parameter

String[ ] args

){

Method Body

myWindow = new JFrame( ); myWindow.setSize(300, 200); myWindow.setTitle(“My First Java Program”); myWindow.setVisible(true); } 22

Template for Simple Java Programs /*

Chapter 2 Sample Program: Displaying a Window

Comment

File: Ch2Sample2.java */

Import Statements

import javax.swing.*; class Ch2Sample1

{

public static void main(String[ ] args) { JFrame

myWindow;

Class Name

myWindow = new JFrame( ); myWindow.setSize(300, 200);

Method Body

myWindow.setTitle(“My First Java Program”); myWindow.setVisible(true); } }

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Why Use Standard Classes 



Don’t reinvent the wheel. When there are existing objects that satisfy our needs, use them. Learning how to use standard Java classes is the first step toward mastering OOP. Before we can learn how to define our own classes, we need to learn how to use existing classes. Example of standard class is JOptionPane

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Sample //My first Java program program public class HelloFTMK { public static void main (String [ ] args ){ System.out.println(“Hello FTMK!”); } }

What to do next…? Save file as : HelloFTMK.java Compile : javac HelloFTMK.java HelloFTMK.class

Run : java HelloFTMK 25

Identifiers 









Names of things such as variables, constants and methods that appear in programs. An identifier must start with a letter, an underscore, or a dollar sign. An identifier consists of letters, digits, underscore and dollar sign. An identifier cannot contain operators, such as +, -, and so on. An identifier cannot be a reserved word. An identifier cannot be true, false, or null. 26

Data Types Category Integral

Data Type

Values

Memory (bytes)

char

0 to 65535

2

byte

-128 to 127

1

short

-32768 to 32767

2

Int

-2147483648 to 2147483647

4

Long

-922337203684547758808 to 922337203684547758807

8

Floating point

float

-3.4E +38 to 3.4E+38

4

Double

-1.7E+308 to 1.7E+308

8

Boolean

True

1 bit

False

1 bit

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Declaring Variables Syntax: dataType identifier1, identifier2,….. identifierN;

int x;

// Declare x to be an // integer variable;

double radius; // Declare radius to // be a double variable; char a;

// Declare a to be a // character variable; 28

Assignment Statements Variable = expression;

x = 1;

// Assign 1 to x;

radius = 1.0;

// Assign 1.0 to radius;

a = 'A';

// Assign 'A' to a;

Declaring and Initializing in One Step int x = 1; double d = 1.4; float f = 1.4;

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Variables // Compute the first area double radius = 1.0; area = radius*radius*3.14159; System.out.println("The area is “ + area + " for radius "+radius); // Compute the second area double radius = 2.0; area = radius*radius*3.14159; System.out.println("The area is “ + area + " for radius "+radius); 30

Constants Syntax: final datatype IDENTIFIER = value; 



Final : specifies that the value stored in the identifier is fixed and cannot be changed. Example: final double PI = 3.14159; final int SIZE = 3;

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Operators 

5 arithmetic operators     





+, addition - , subtraction * , multiplication / , division % , mod

Unary : an operator that has only one operand Binary : an operator that has two operand 32

Arithmetic Operators 

The following table summarizes the arithmetic operators available in Java.

This is an integer division where the fractional part is truncated.

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The boolean Type and Operators boolean lightsOn = true; boolean lightsOn = false;

  

&& (and) || (or) ! (not)

(1 < x) && (x < 100) (lightsOn) || (isDayTime) !(isStopped) 34

Operator Precedence Casting ++,--(preincrement,predecrement) *, /, % +, <, <=, >, >= ==, !=; &&, & ||, | =, +=, -=, *=, /=, %=

LOW 35

Operators 

Example of arithmetic operators 

5/2 yields an integer 2.



5.0/2 yields a double value 2.5



5 % 2 yields 1 (the remainder of the division)



-34 % -5 yields -4



4 % 6 yields 4

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Example program public class MixedExpression { public static void main( String[] args ) { System.out.println(“3 / 2 + 5.0 = ” + (3 / 2 + 5.0)); System.out.println(“4 * 3 + 7 / 5 – 25.5 = ” + (4 * 3 + 7 / 5 – 25.5 )); } Sample Run: } 3 / 2 + 5.0 = 6.0 4 * 3 + 7 / 5 – 25.5 = -12.5

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Shortcut Operators Operator Example

Equivalent

+=

i+=8

i = i+8

-=

f-=8.0

f = f-8.0

*=

i*=8

i = i*8

/=

i/=8

i = i/8

%=

i%=8

i = i%8

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Increment and Decrement Operators     

Pre-increment : ++variable Post-increment : variable++ Pre-decrement : --variable Post-decrement : variable-Example: 



a = 5; b = 2 + (++a); // a is 6, b is 8 a = 5; b = 2 + (a++); // a is 6, b is 7

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Numeric Type Conversion Consider the following statements: byte i = 100; long l = i*3+4; double d = i*3.1+l/2; int x = l; (Wrong) long l = x; (fine, implicit casting)

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Type Casting      

double float long int short byte

Implicit casting double d = 3; (type widening) Explicit casting int i = (int)3.0; (type narrowing)

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Example program public class ExampleCasting { public static void main( String[] args ) { System.out.println(“(int)(7.9) = ” + (int)(7.9) ); System.out.println(“(int)(7.8 + (double)(15/2)) = ” + ((int)(7.8 + (double)(15/2)))); System.out.println(“(int)(7.8 + (double)(15) / 2 ) = ” + ((int)(7.8 + (double)(15)/2))); } } Output: (int)(7.9) = 7 (int)(7.8 + (double)(15/2)) = 14 (int)(7.8 + (double)(15) / 2 ) = 15

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Type Mismatch 

Suppose we want to input an age. Will this work? int

age;

age = JOptionPane.showInputDialog( null, “Enter your age”);

• No. String value cannot be assigned directly to an int variable. 43

Type Conversion 

Wrapper classes are used to perform necessary type conversions, such as converting a String object to a numerical value. int String

age; inputStr;

inputStr = JOptionPane.showInputDialog( null, “Enter your age”); age = Integer.parseInt(inputStr);

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Other Conversion Methods

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Sample Code Fragment //code fragment to input radius and output //area and circumference double radius, area, circumference; radiusStr = JOptionPane.showInputDialog( null, "Enter radius: " ); radius = Double.parseDouble(radiusStr); //compute area and circumference area = PI * radius * radius; circumference = 2.0 * PI * radius; JOptionPane.showMessageDialog(null, "Given Radius: " + radius + "\n" + "Area: " + area + "\n" + "Circumference: " + circumference); 46

Character Data Type char letter = 'A'; (ASCII) char numChar = '4'; (ASCII) char letter = '\u000A'; (Unicode) char letter = '\u000A'; (Unicode) Special characters char tab = ‘\t’; 47

Unicode Format Description

Escape Sequence

Unicode

Backspace

\b

\u0008

Tab

\t

\u0009

Linefeed

\n

\u000a

Carriage return \r

\u000d

48

Strings and the operator + 





Concatenate operations allows a string to be appended at the end of another string ‘+’ is used to concatenate two strings, a string and a numeric value or a character. Example: String str; str = “Sunny”; str = str + “ Day ”; After the statements executes, the string assigned to str is: Sunny Day 49

Example Program public class ExampleString { public static void main (String[] args) { String str; int num1,num2; num1 = 12; num2 = 26; str = num1 + num2; System.out.println(“str 1 : ” + str); str = (num1 + num2); System.out.println(“str 2 : ” + str); } }

Output: str1 : 1226 str2 : 38

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Input 

To put data into variables from the standard input device, you first create an input stream object and associate it with the standard input device static Scanner console = new Scanner(System.in); Scanner is a predefined Java class, console is the object of this class.

51

Input 

The object console reads the next input as follows: 









If the next input can be interpreted as an integer console.nextInt() If the next input can be interpreted as a floating-point number console.nextDouble() If the next input can be interpreted as a string console.next() If the next input can be interpreted as a string until the end of the line console.nextLine()

console.nextInt(), console.nextDouble() and console.next() skip any whitespace characters 52

Output 



Standard output device is accomplished by using standard output object System.out. It has two methods 



print - leaves the insertion point after the last character of the value of expression System.out.print (expression); println – insertion point at the beginning of the next line System.out.println (expression); System.out.println (); - only positions the insertion point at the beginning of the next line

53

Example Program import java.util.*; // required to use the class Scanner public class InputOutput { static Scanner console = new Scanner(System.in); public static void main(String[] args) { int feet, inches; System.out.println(“Enter 2 integers :”); Output: Enter 2 integers: feet = console.nextInt(); 23 7 inches = console.nextInt(); System.out.println (“Feet = ” + feet); System.out.println (“Inches = ” + inches);

Feet = 23 Inches = 7

} } 54

Output using JOptionPane 

Using showMessageDialog of the JOptionPane class is a simple way to display a result of a computation to the user. JOptionPane.showMessageDialog(null, “I Love Java”);

This dialog will appear at the center of the screen.

55

Displaying Multiple Lines of Text  We can display multiple lines of text by separating lines with a new line marker \n. JOptionPane.showMessageDialog(null, “one\ntwo\nthree”);

56

Sample program 

Product.java - Calculate the product of three integers.

57

// Product.java - Calculate the product of three integers. // Java packages import javax.swing.JOptionPane;

Sample program (with GUI)

public class Product { public static void main( String args[] ) { int x; // first number int y; // second number int z; // third number int result; // product of numbers String xVal; // first string input by user String yVal; // second string input by user String zVal; // third string input by user xVal = JOptionPane.showInputDialog( "Enter first integer:" ); yVal = JOptionPane.showInputDialog( "Enter second integer:" ); zVal = JOptionPane.showInputDialog( "Enter third integer:" ); x = Integer.parseInt( xVal ); y = Integer.parseInt( yVal ); z = Integer.parseInt( zVal ); result = x * y * z; JOptionPane.showMessageDialog( null, "The product is " + result ); System.exit( 0 ); } // end method main } // end class Product

58

Programming Style and Documentation Appropriate Comments  Naming Conventions  Proper Indentation and Lines  Block Styles 

Spacing

59

Appropriate Comments 



Include a summary at the beginning of the program to explain what the program does, its key features, its supporting data structures, and any unique techniques it uses. Include your name, class section, instruction, date, and a brief description at the beginning of the program.

60

Naming Conventions  





Choose meaning and descriptive names. Variables and method names:  Use lowercase. If the name consists of several words, concatenate all in one, use lowercase for the first word, and capitalize the first letter of each subsequent word in the name. For example, the variables radius and area, and the method computeArea. Class names:  Capitalize the first letter of each word in the name. For example, the class name ComputeArea. Constants:  Capitalize all letters in constants. For example, the constant PI.

61

Proper Indentation and Spacing 

Indentation 



Indent two spaces.

Spacing 

Use blank line to separate segments of the code.

Block Styles 

Use next-line style for braces. 62

Programming Errors 

Syntax Errors 



Runtime Errors 



Detected by the compiler Causes the program to abort

Logic Errors 

Produces incorrect result

63

Problem Statement 

Problem statement: Write a loan calculator program that computes both monthly and total payments for a given loan amount, annual interest rate, and loan period.

Overall Plan 

Tasks: 

 

Get three input values: loanAmount, interestRate, and loanPeriod. Compute the monthly and total payments. Output the results.

64

Required Classes

65

Development Steps We will develop this program in four steps: 2.

3. 4.

5.

Start with code to accept three input values. Add code to output the results. Add code to compute the monthly and total payments. Update or modify code and tie up any loose ends. 66

Step 1 Design 

Call the showInputDialog method to accept three input values:   



loan amount, annual interest rate, loan period.

Data types are Input

Format

Data Type double

loan amount

dollars and cents

annual interest rate

in percent (e.g.,12.5)

double

loan period

in years

int 67

Step 1 Code Program source file is too big to list here. From now on, we ask you to view the source files using your Java IDE.

Directory:

Chapter3/Step1

Source File: Ch3LoanCalculator.java

68

Step 1 Test 

In the testing phase, we run the program multiple times and verify that  

we can enter three input values we see the entered values echo-printed correctly on the standard output window

69

Step 2 Design  

We will consider the display format for out. Two possibilities are (among many others)

70

Step 2 Test 



We run the program numerous times with different types of input values and check the output display format. Adjust the formatting as appropriate

71

Step 3 Design 





The formula to compute the geometric progression is the one we can use to compute the monthly payment. The formula requires the loan period in months and interest rate as monthly interest rate. So we must convert the annual interest rate (input value) to a monthly interest rate (per the formula), and the loan period to the number of monthly payments. 72

Step 3 Test 

We run the program numerous times with different types of input values and check the results.

73

Step 4: Finalize  

We will add a program description We will format the monthly and total payments to two decimal places using DecimalFormat.

74

Exercises 1.

2.

Suppose you need to write a Java program that calculates an employee's paycheck for a given number of hours of work. Write declarations for the variables you'll need. Using the variables you declared in exercise 1, write the program lines needed to perform the paycheck calculations.

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