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Chapter 1

Introduction to

Computers and Java

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Chapter 1

1.1 Computer Basics

1.2 A Sip of Java

1.3 Programming Basics

1.4 Graphics Supplement

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1.1 Computer

Basics

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The CPU is the brain

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Memory is the storage

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RAM is volatile

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Secondary memory is permanent

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Memory is byte addressable

1000

999

998

997

996

995

994

993

0000 0000

0000 0000

0000 0000

0000 0001

1000 0001

1

'A'

4 byte memory locationat address

8 bits = 1 byte

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Programmers writeprograms

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Computers executeprograms

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Programs must betranslated

Java code Machine code

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Using a Compiler<Compile once – run many>

Source codeHigh level

CompilerAssembly code

Low level Binary codeMachine level

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Using an Interpreter<Compile-run cycle>

InterpreterSource code

High level

Assembly codeLow level

Binary codeMachine level

Programexecution

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The Java way usesboth techniques

Java Virtual Machine<Interpreter>

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A class loader combinesall the bytecode files

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1.2 A Sip of Java

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Text Application Deconstructed<FirstProgram.java>

import java.util.Scanner;

System.out.println("Please enter two numbers and"); System.out.println("I will compute their sum.");

int n1; int n2; Scanner keyboard = new Scanner(System.in); n1 = keyboard.nextInt(); n2 = keyboard.nextInt(); System.out.println("Their sum is"); System.out.println(n1 + n2); }// end main()

public static void main(String[] args) {

public class FirstProgram{

}// end FirstProgram

Program uses the scanner

class

Inform the user

Declare variables Read from

the keyboard

Give user an answer

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Text Application Deconstructed<output>

Please enter two numbers andI will compute their sum.10 30Their sum is40

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GUI Program Deconstructed<HappyFace.java>

package happyface;

import javax.swing.JFrame;import java.awt.Graphics;

public class HappyFaceApplet extends JFrame { @Override public void paint(Graphics canvas) {

}}

canvas.drawOval(100, 50, 200, 200); canvas.fillOval(155, 100, 10, 20); canvas.fillOval(230, 100, 10, 20); canvas.drawArc(150, 160, 100, 50, 180, 180);

Classes we need for GUI

programs

Using drawing commands

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GUI Program Deconstructed<HappyFace.java>

public HappyFace() { setSize(600, 400); setDefaultCloseOperation(EXIT_ON_CLOSE); }// end HappyFace()

public static void main(String[] args) { HappyFace guiWindow = new HappyFace(); guiWindow.setVisible(true); }// end main() }// end HappyFace

Set window's initial width and

height

Initialize the window and

make it visible

Exit program when window is

closed.

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1.3 Programming

Basics

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Java is OO

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Objects can representmany things

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A class providesthe blueprint

Car

Attributes<instance variables>

Behavior <methods>

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OOP is based onthree pillars

Encapsulati

on

Inhe

ritan

ce

Polymorph

ism

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Encapsulation = Information Hiding

You can drive a car, but you may not know how an engine works.

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Inheritance = Reuse / Extend

Objects can be reused

Objects can be extended

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Polymorphism = React in own way

Come back!

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Before coding beginsdevelop your algorithms

Algorithms come inmany flavors

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Once coding beginsbe aware of bugs

Syntax – Grammar not followed

Run-time – Computer can't honor request

Logic – Programmer slip

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1.4Graphics

Supplement

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The Coordinate System

(0,0)

(100, 50)

X

Y

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Drawing an Oval

(0,0)

(100, 50)

X

Y

canvas.drawOval(100, 50, 100, 100);

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Filling an Oval

(0,0)

(100, 50)

X

Y

canvas.fillOval(155, 100, 10, 20);

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Filling an Oval

(0,0)

(100, 50)

X

Y

canvas.fillOval(230, 100, 10, 20);

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Drawing an Arc

(0,0)

(150, 160)

X

Y

canvas.drawArc(150, 160, 100, 50, 180, 180);