An intro to programming

The purpose of writing a program is to solve a problem or take advantage of an opportunity

Consists of multiple steps:Understanding problem or opportunity.Breaking the problem into manageable pieces (decomposing).Designing a solution.Considering alternatives to the solution and refining the solution.Implementing the solution. Testing the solution and fixing the problems.

What is a program?

• A program is computer coding that:

• Takes input• Performs some

calculation on the input

• Displays output

What is a program?

• A program is…– A collection of statements– Written in a programming language– A specification of the steps taken to

solve a problem

• Programs have grammar rules– Specify how the statements are formed– How the statements are combined

Writing programs

• You need:– Knowledge of a coding language– Problem solving skills– Familiarity with analysis and

design process– Software development tools

Programming Language Hierarchy

H ard w are

M ach in e L an g u ag e

A ssem b ly L an u ag e

H ig h -L eve l L an g u ag e (H L L )

The highs and lows of programming languages ...

• High-Level Language (HLL)– closest to natural

language– words, numbers, and

math symbols– not directly understood

by hardware– “portable” source code

(hardware independent)– Java, C, C++, COBOL,

FORTRAN, BASIC, Lisp, Ada, etc.

• Machine Language(lowest level)– least natural language for

humans, most natural language for hardware

– just 0s and 1s– directly understood by

hardware– not portable (hardware

dependent)

In order for a program to run on a computer, it must be in that computer’s machine language. Each type of CPU has it’s own language.

Getting from Sourceto Machine Code

• “Compiling a program”translating from a high-level language source code to machine

(object, or executable) code.

• “Compiler”a program that translates HLL source code to machine (object,

or executable) code.

• “Assembly”translating from assemble language source code to machine

(object, or executable) code.

• “Assembler”a program that translates assembly source code to machine

(object, or executable) code.

• Compilers need to know the specific target hardware

Compilers vs. Assemblers vs. Interpreters

• Compilers and Assemblers– translation is a separate user step– translation is “off-line,” i.e. not at run time

• Interpreters - another way to translate source to object code– interpretation (from source to object code) is not a

separate user step– translation is “on-line,” i.e. at run time

SourceCode

Java Program Translation• Both Compilation and

Interpretation• Intermediate Code:

“Byte Code”– portable low-level

code– similar to assembly

code,but hardware independent

– invisible to Java programmer

• Interpreter translates from generic byte code to hardware-specific machine code

Java Program Data for Java Program

Java Compiler

Byte-CodeProgram

Byte-Code Interpreter

Machine-LanguageInstructions

Computer Executionof Machine-Language Instructions

Output of Java Program

JavaVirtualMachine

1

Basic Program Development

errors

errors

Edit andsave program

Compile program

Execute program andevaluate results

The Java Software Development Kit (SDK)

• Can be downloaded free from Sun website.

• a development environment for building applications, applets, and components using the Java programming language

• These tools are designed to be used from the command line. Except for the appletviewer, these tools do not provide

a Graphical User Interface

Java

• Java was released in 1995 by Sun Microsystems.

• It is written in the language C++.

• Java is platform-independent, object-oriented, and easy to use on the Internet.

STOP

A closer look at Java SDK and JCreator IDE.

Java™ SDK, Standard Edition • a development environment for

building applications, applets, and components using the Java programming language

• includes tools useful for developing and testing programs written in the Java programming language and running on the Java platform

• Except for the appletviewer, these tools do not provide a graphical user interface

API Specification

• Application Programming Interface (API) documentation online and downloadable

• Contains detailed documentation on all classes and packages in the java standard library

• java API Specification

The Java Virtual Machine (JVM) – key to portability

• is an abstract (virtual) computer that runs compiled Java programs – virtual" because it is generally implemented in

software on top of a "real" hardware platform and operating system

•Makes java code portable

•code compiled on any platform will run on any other platform having Java Virtual Machine

For Home ComputerDownload and Install

JCreator LEJSDKJava API documentation

All from jcreator.com/download.htm

Organizing Work• The H drive is your personal workspace in the

classroom.• Create folders to organize work by topic, week,

semester …

Your first Java Program

• Start Jcreator• Follow instructions to create a Java

program named HelloWorldpublic class HelloWorld{

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

}

Your first Java Programpublic class HelloWorld{

public static void main(String[] args)

{System.out.println(“Hello

World”);}

}

Creation of a .class file - bytecode

• Go back to your project directory and look at the new files:– HelloWorld.java – source code– HelloWorld.class - bytecode

On Your Own

• Open HelloWorld source code and add more output lines.

• Open java program named Basics – Compile, execute, modify, compile …