chapter 8: introduction to high-level language programming

Chapter 8: Introduction to High-Level Language ProgrammingInvitation to Computer Science,

Java Version, Third Edition

Invitation to Computer Science, Java Version, Third Edition 2

Objectives

In this chapter, you will learn about

Where do we stand?

High-level languages

Introduction to Java

Virtual data storage

Statement types


Objectives (continued)

Meeting expectations

Managing complexity

Object-oriented programming

Graphical programming

The big picture: Software engineering


Where Do We Stand? Early days of computing

Programmers were satisfied with assembly language Programs mostly written by very technically

oriented people

Later decades Programmers demanded a more comfortable

programming environment Programs were now also written by “nontechie”

people


High-Level Languages

High-level programming languages

Called third-generation languages

Created to overcome deficiencies of assembly language

Expectations of a high-level language program

The programmer need not manage the details of the movement of data items within memory nor exactly where those items are stored


High-level Languages (continued) Expectations of a high-level language program

(continued)

Programmer can take a macroscopic view of tasks; “primitive operations” can be larger

Program will be portable

Programming statements will be closer to standard English and use standard mathematical notation


Transition of a High-level Language Program

High-level langauge program

compiler Low-levelcode

Secondtranslator

Object code in machine langauge

linkerComplete object code

Executable module loaded into memory

Harware Resultes


Introduction to Java: A Simple Java Program Comments

Give information to human readers of code Class header

Announces that a class is about to be defined Class

A collection of methods Method

A section of code that performs a service


Figure 8.2 A Simple Java Program


Running a Java Program

File containing the Java code Same name as the class File extension .java Example: TravelPlanner.java

Running a Java program Program compiled

Example: File TravelPlanner.class created Translation to object code completed; program

linked, loaded, and executed


Virtual Data Storage

Identifiers Names in a programming language

Keyword Has a special meaning in Java

Java is a case-sensitive, free-format language Variable

A named location in memory Must be declared before it can be used


Figure 8.4

Some of the Java Primitive Data Types


Virtual Data Storage (continued) An array

Groups together a collection of memory locations, all storing data of the same type

Figure 8.5

A 12-Element Array Hits


Statement Types

Input/output statements

Input statement

Collects a specific value from the user for a variable within the program

Output statement

Writes a message or the value of a program variable to the user’s screen or to a file


Statement Types (continued)

Assignment statement

Assigns a value to a program variable

Control statement

Directs the flow of control

Can cause it to deviate from the usual sequential flow


Input Statements

A prompt

A message that tells the user what kind of input the program wants

Console class

Not a standard Java class; written for this book

Can be used to handle both the prompt and the retrieval of the value in one statement


Input Statements (continued)

Methods readInt

readDouble

readChar

Syntax

variable1 = Console.readInt(prompt);

variable2 = Console.readDouble(prompt);

variable3 = Console.readChar(prompt);

Eg

public class TravelPlanner { public static void main(String[] args) { int speed = 1; double distance = 0; double time;

speed = Console.readInt("Enter speed in mph:"); distance = Console.readDouble("Enter your distance in miles;"); time = distance/speed; System.out.print("At " + speed + "mph, it will take " + time + "hours to travel " +

distance + " miles"); } }



Output Statements

Output to the screen

System.out.println(string);

The string can be Empty

System.out.println();

Literal stringSystem.out.println("Here's your answer." );

Composed of two or more itemsSystem.out.println("Give me " + 5);


The Assignment Statement

General form

variable = expression;

Expression is evaluated first; the result is written into the memory location specified on the left


The Assignment Statement (continued)

Examples

B = 2; Suppose that B is an integer variable

A = B + C; Suppose that A, B, and C are integer variables

Letter = 'm'; Suppose that Letter is a variable of type char

Type casting: happen when an integer value is assigned to a double value.

Initialize variable as soon as they they declared, like: int count = 0;



Control Statements

Types of control mechanisms Sequential

Instructions are executed in order

Conditional The choice of which instructions to execute next

depends on some condition

Looping A group of instructions may be executed many

times


Control Statements (continued) Sequential is default mode of execution

Conditional flow of control

Evaluation of a Boolean condition (also called a Boolean expression)

The programming statement to execute next is based on the value of the Boolean condition (true or false)


Control Statements (continued) Conditional flow of control (continued)

if-else statement

if (Boolean condition)

S1;

else

S2;

if variation of the if-else statement

if (Boolean condition)

S1;

S1, S2 may be compound statement (may have serval statements)


Figure 8.10

Conditional Flow of Control

(If-Else)


Figure 8.11

If-Else with Empty Else

Comparison Operator

Symbol Example Example Result

== 2==5 F

< 2<5 T

<= 2<=5 T

> 2>5 F

>= 2>=5 F

!= 2!=5 T


Boolean Operator

Operator Symbol Eg Eg result

AND && (2<5)&&(2>7) F

OR || (2<5)||(2>7) T

NOT ! !(2==5) T


public class TravelPlanner

{

public static void main(String[] args)

{

int speed = 1;

double distance = 0;

double time;

int hours = 0;

int minutes = 0;

char choice = 'M';

speed = Console.readInt("Enter speed in mph:");

distance = Console.readDouble("Enter your distance in miles;");

choice = Console.readChar("Decimal hours or hours and mins");

if (choice == 'D')

{

time = distance/speed;

System.out.print("At " + speed + "mph, it will take " + time + "hours to travel " + distance + " miles");

}

else

{

time = distance/speed;

hours = (int) time;

minutes = (int)((time - hours)*60);

System.out.print("At " + speed + "mph, it will take " + hours + " hours " + minutes + " minutes " + distance + " miles");

}

}

}



Control Statements (continued) Looping (iteration)

The loop body may be executed repeatedly based on the value of the Boolean condition

while statement

while (Boolean condition)

S1;


Figure 8.13

While Loop

public class TravelPlanner {

public static void main(String[] args) {

int speed = 1;

double distance = 0;

double time;

int hours = 0;

int minutes = 0;

char choice = 'M';

char more = 'Y';

more = Console.readChar("Want to plan a trip? (Y or N):");

while (more == 'Y') {

speed = Console.readInt("Enter speed in mph:");

distance = Console.readDouble("Enter your distance in miles;");

choice = Console.readChar("Decimal hours or hours and mins: ");

if (choice == 'D') {

time = distance / speed;

System.out.print("At " + speed + " mph, it will take " + time + " hours to travel " + distance + " miles ");

} else {

time = distance / speed;

hours = (int) time;

minutes = (int) ((time - hours) * 60);

System.out.print("At " + speed + " mph, it will take " + hours + " hours " + minutes + " minutes " + distance + " miles ");

}

}


more = Console.readChar("Want to plan another trip? (Y or N):");

}

}


Another Example

Algorithm (Psudo code)

Get value for user’s choice about continuing

While user wants to continue, do the following steps

Get value for pool radius

Get value for choice of task

If taske choice is circumference

Compute pool circumference

print output

Else (task to aread)

Compute pool area

print output

Get value for user’s choice about continuing

Stop


public class SportsWorld {


double radius = 0.0;

double circumference = 0.0;

double area = 0.0;

char taskToDo = ' ';

char more = 'Y';

more = Console.readChar("Want to process a pool? (Y or N):");



radius = Console.readDouble("Enter the value of radius:");

System.out.println("Enter your choice of task: ");

taskToDo = Console.readChar("C to circumference; A to compute area ");

if (taskToDo == 'C') {

circumference = 2 * Math.PI * radius;

System.out.print("The circumference for a pool of radius " + radius + " is " + circumference);

} else {

area = Math.PI * radius * radius;

System.out.print("The area for a pool of radius " + radius + " is " + area);

}


more = Console.readChar("Want to process another trip? (Y or N):");

}

}

}



Meeting Expectations

Java meets the four expectations for a high-level programming language

Expectations

The programmer need not manage the details of the movement of data items within memory nor pay any attention to where specifically they are stored


Meeting Expectations (continued) Expectations (continued)

The programmer can take a macroscopic view of tasks, thinking at a higher level of problem solving

Programs written in high-level languages will be portable rather than machine-specific

Programming statements in a high-level language

Will be closer to standard English

Will use standard mathematical notation


Managing Complexity: Divide and Conquer

Divide and conquer

Divide the problem into small pieces

In a computer program

Divide the code into modules or subprograms, each of which does some part of the overall task

Empower these modules to work together to solve the original problem


Figure 8.20 Structure Charts


Using Methods

Method

A module of code in Java

Named using ordinary Java identifiers

By custom, name starts with a lowercase letter


Using Methods (continued)

Two types of methods

void method Does not pass any value back to the main method

nonvoid method Returns a single new value back to the main method

Overall form of a method invocation

method-identifier(argument list) (same class)

class-identifier.method-identifier(argument list) (different class)

public class SportsWorld {


double radius = 0.0;

double circumference = 0.0;

double area = 0.0;

char taskToDo = ' ';

char more = 'Y';

more = Console.readChar("Want to process a pool? (Y or N):");



radius = Console.readDouble("Enter the value of radius:");

System.out.println("Enter your choice of task: ");

taskToDo = Console.readChar("C to circumference; A to compute area ");


if (taskToDo == 'C') {

circumference = doCircumference(radius);

System.out.print("The circumference for a pool of radius " + radius + " is " + circumference);

} else {

area = doArea(radius);

System.out.print("The area for a pool of radius " + radius + " is " + area);

}


more = Console.readChar("Want to process another trip? (Y or N):");

}

}

42

public static double doCircumference(double radius)

{

double circumference = 0;

circumference = 2 * Math.PI * radius;

return circumference;

}

public static double doArea(double radius)

{

double area = 0;

area = Math.PI * radius * radius;

return area;

}

public static void Prompt(double radius)

{

System.out.println(“radius: “ + radius);

}

}



Writing Methods

General form of the method headerscope-indicator return-indicator identifier(parameter list)

Arguments in Java are passed by value

A variable declared within a method can be used only within that method

Return statement Syntax

return expression;


Figure 8.27

Some Java Terminology


Object-Oriented Programming: What Is It? Object-oriented programming (OOP)

A program is a simulation of some part of the world that is the domain of interest

Each object is an example drawn from a class of similar objects

Key elements of OOP Encapsulation

A class consists of its subtask modules and its properties, and both components are “encapsulated” with the class


What Is It? (continued)

Key elements of OOP (continued)

Inheritance

Once a class A of objects is defined, a class B of objects can be defined as a “subclass” of A

Polymorphism

One name, the name of the service to be performed, has several meanings, depending on the class of the object providing the service


Java and OOP

Java is an object-oriented programming language

Objects: Instances of a class

Instance variables: Properties

Instance methods: Services

Static method Can be invoked by giving the class name, a dot,

the method name, and a list of arguments. Use class to call static method


Java and OOP (continued)

Syntax to request an object to invoke a method

object-identifier.method-identifier(argument list)

Calling object

The object that invokes a method

package myproject; public class SportsWorld { public static void main(String[] args) { double newRadius = 0.0; char taskToDo = ' '; char more = 'Y'; Circle SwimmingPool = new Circle(); more = Console.readChar("Do you want to prcess a new pool? (Y or N): "); while (more == 'Y') { System.out.println(); newRadius = Console.readDouble("Enter the value to the radius of the pool: "); SwimmingPool.setRadius(newRadius); System.out.println("Enter your choice of task."); taskToDo = Console.readChar("C to compue ciucumference, A to compute area: "); System.out.println(); if (taskToDo == 'C') System.out.println("the ciccumference for a pool radius " + SwimmingPool.getRadius() + " is " + SwimmingPool.doCircumference()); else System.out.println("the area for a pool radius " + SwimmingPool.getRadius() + " is " + SwimmingPool.doAreaY());

more = Console.readChar("Do you want to prcess a new pool? (Y or N): "); } } }


public class Circle {

public void setRadius(double value)

{

radius =value;

}

public double getRadius()

{

return radius;

}

public double doCircumference()

{

return 2 * Math.PI * radius;

}

public double doArea()

{

return Math.PI * radius * radius;

}

private double radius;

}


One more examplepublic class Circle {

public void setRadius(double value)

{

radius =value;

}

public double getRadius()

{

return radius;

}

public double doCircumference()

{

return 2 * Math.PI * radius;

}


{

return Math.PI * radius * radius;

}

private double radius;

}


public class Rectangle {

public void setWidth(double value)

{

width =value;

}

public void setHeight(double value)

{

height =value;

}

public double getWidth()

{

return width;

}

public double getHeitgh()

{

return height;

}


{

return width * height;

}

protected double width, height;

}


public class Square {

public void setSide(double value)

{

side = value;

}

public double getSide()

{

return side * side;

}


{

return side * side;

}

private double side;

}Invitation to Computer Science, Java Version, Third Edition 54

public class Square2 extends Rectangle{

public void setSide(double value)

{

width = value;

height = value;

}

}


public class Ceometry {


Circle joe = new Circle();

joe.setRadius(23.5);

System.out.println("The area of a circle with radius " + joe.getRadius() + " is " + joe.doArea());

Rectangle luis = new Rectangle();

luis.setWidth(12.4);

luis.setHeight(18.1);

System.out.println("The area of a rectangle with dimensions " + luis.getWidth() + " and " + luis.getHeight() + " is " + luis.doArea());

Square anna = new Square();

anna.setSide(3);

System.out.println("The area of a square with side " + anna.getSide() + " is " + anna.doArea());

Square2 tyler = new Square2();

tyler.setSide(4.2);

System.out.println("The area of a square with side " + tyler.getWidth() + " is " + tyler.doArea());

}

}



What Have We Gained?

Two major advantages of OOP

Software reuse

A more natural “world view”


Graphical Programming: Graphics Hardware

Bitmapped display The screen is made up of thousands of individual

picture elements, or pixels, laid out in a two-dimensional grid

Frame buffer Memory that stores the actual screen image

Terminal hardware displays the frame buffer value of every individual pixel on the screen


Figure 8.34

Pixel Numbering System in a Bitmapped Display


Graphics Software

Graphics library Contains a collection of software routines that

control the setting and clearing of pixels

Abstract Windowing Toolkit (AWT) Contains routines that allow users to create

powerful interfaces

Swing components Even more powerful GUI components than AWT


Graphics Software (continued) Graphics class

Contains drawing commands that allow you to

Draw geometric shapes (lines, rectangles, ovals, polygons, and so on)

Set, change, and define colors

Fill in or shade objects

Create text in a range of fonts and sizes

Produce graphs and charts

Egimport java.awt.*;

public class Graph {


Frame f = new Frame("Eg 1");

f.setSize(500, 500);

f.setVisible(true);

Graphics g;

g = f.getGraphics();

g.setColor(Color.blue);

while (true)

{

g.drawLine(168, 112, 112, 168);

g.drawOval(100, 100, 80, 80);

g.drawString("No Entry", 112, 145);

}

}

}


Other functions

drawRect(int x, int y, int width, int height); drawRoundRect(int x, int y, int width, int

height, int arcWidth, int arcHeight); fillRect(int x, int y, int width, int height); fillRoundRect(int x, int y, int width, int height,

int arcWidth, int arcHeight); fillOvel(int x, int y, int width, int height);



The Big Picture: Software Engineering Software life cycle

The overall sequence of steps needed to complete a large-scale software project

Implementation represents a relatively small part of the cycle


Figure 8.36

Steps in the Software Development Life Cycle


Scaling Up

Programs written by students No longer than a few hundred lines

Real-world programs 2, 3, or 4 orders of magnitude larger

Large-scale software development Extensive planning and design needed

A team of programmers needed

Software engineering


The Software Life Cycle

Each step in the software development life cycle

Has a specific purpose and activities

Should result in a written document

The feasibility study

Problem specification

Program design


The Software Life Cycle (continued) Algorithm selection or development, and

analysis

Coding

Debugging

Testing, verification, and benchmarking

Documentation

Maintenance


Modern Environments

Integrated Development Environment (IDE) speeds program development by providing

A text editor

A file manager

A compiler

A linker and loader

Tools for debugging


Summary

In a high-level language, the programmer

Need not manage storage nor movement of data values in memory

Can use more powerful program instructions that are more like natural language

Can write a much more portable program

Java is an object-oriented, high-level programming language


Summary (continued)

In Java, an if-else statement can be used to create a conditional flow of control

In Java, a while loop can be used for iteration

Software life cycle: Overall sequence of steps needed to complete a large-scale software project

chapter 8: introduction to high-level language programming

Documents

java version

computer science

java codesame

java programfile

simple java programinvitation

movement of data items

file travelplanner

class createdtranslation