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Introduction to Java

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What is Java

Developed in the early 1990s by Sun

Meant to be highly portable so it could beembedded into microwave ovens, cell

phones, remote controls, etc

Java was written with the C language

Has similar syntax to C, C++, and JavaScript

(JavaScript is totally different than Java)

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Java is Platform Independent

Java can be run on any platform or any

processor that has a JVM built for it. Java is an interpreted language, meaning

that there is a machine/processor-dependent

interpreter called the JVM that translates the

standard Java code into instructions for thespecific processor

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Java Architecture

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Platform Independence

In C++, only the source code is platform

independent; the compiler and executableare platform-dependent

Microsoft.NET products are Platform

Dependent but Language Independent to a

degree

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Garbage collection and the JVM

In addition to converting your common

bytecode to machine-dependent instructions,the JVM provides memory cleanup known as

garbage collection

The JVM will clean up after a program once

components are no longer needed (i.e. youdont need stuff like set x = nothing).

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Java Libraries and Open Source

Java includes many reusable tools and

objects that are part of the language Additional open-source tools and classes can

be found on the web that have been built by

the open source community and can be re-

used in your applications

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Java is object-oriented

Concept Description Example

Class Job Description Instructor

Method Task doLecture()Package Collection of classes itt.common

Object Instance of a class russellDobda

All code must be written as classes!

Java is Case Sensitive!

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3 types of Java Programs

1. Java Application

Standalone; run from command line2. Java Applet

Runs in a web browser

Downloaded from server and run client-side

3. Java Servlet

Resides and runs on web server

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Java Servlets and JSP

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System Development

Always plan before you code. Understand the

problem and plan a solution.

Always test. Test driven development encourages

writing tests first and creating automated build

scripts that run the tests

Dont wait until the last minute! Count on building a

program over several days.

Assume you will be rethinking and refactoring as

you go; just like writing a novel

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Phases of the Software Development Life Cycle

Needs Analysis: The Why

Define the problem Requirements Analysis: The What

Define the solution in terms of businessrequirements

Consideration of Who and Where

Design: The How High Level and Detailed Design Flow charts, psuedocode

Development

Construction of the Software and unit testing Unit Testing (Unit, Integration)

Testing: User Acceptance, System Testing Implementation

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Programming in Java

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Java Coding - Comments

//this is a comment

/* this is amulti-line comment */

/** this is javadoc documentation* that contains standard information* @author Russell Dobda*/

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Java Coding Class definitions

public class MyClass {//your code here

}

Every java program must contain at least one

Usually, each .java file will contain a singleclass

The filename must match the class name

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Java Application main() method

public class MyClass{

public static void main(String args[])

{

System.out.println(Hello World!);

}

}Question: what are the inputs and outputs of

the main method?

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Standards

Java ignores whitespace, so you can use as

much or as little as you want, but pleasemaintain readibility!!

Bracket positioning (two standards, use

either)

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Primitive data types

Java includes 8 primitive (non-object) data types. They

begin with a lower-case

boolean int

byte long

char float

short double

See page 50

for detailed

descriptions

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Declaring variables in Java

data_type variable_name;

Examplesfloat balance;

float balance = 2000.0;

float balance, deposit, withdrawal;

float balance=2000.0, deposit=50.0;

You should always initialize your variables to

at least null or 0

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The String Class

Java class that has many built-in methods forreplace, find, case, etc

Concatenate strings with the + operator

String instructorName = Mr. Dobda;

System.out.println(Your instructoris + instructorName);

Note that System.out.println allows you towrite a line of text to the output console

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Escape sequences for strings

Sequence Result Example

\ Quotes value = He said \Hello\

\n New

line

value = Are you sure\n

you want to do this?

\\ Back-

slash

Value = Go to c:\\My

Documents

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Final variables (aka constants)

These values cannot be modified

Use all caps with underscores

public final String SCHOOL_LOCATION = ITT;

If public, it can be referenced from other classes

System.out.println(You go to +

MyClass.SCHOOL_LOCATION);

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Naming conventions

Class: Descriptive noun or noun phrases.Starts with caps and uses caps for each word

Method: start with lower case, use caps foreach subsequent word

Variable: same as methods. Be descriptive!

Use single letter variable names only for loopindexes

Final variable: CAPS_WITH_UNDERSCORE

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Java Operators

See page 57 for full list

and precedence

Question: what is the

precedence of the

following:

fTemp = 9.0/5.0 *cTemp + 32.0;

! Logical not

== Same as

!= Not same as

&& Conditional and

|| Conditional or= Assignment

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Assignment operator (=)

//valid assignments

a = 1;b = 2;

a = b = c = 0;

double x = 32.0;//invalid assignment

32 = z;

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Casting Variables

You can cast variables from one type toanother when direct assignment is not an

option:float f = (float)9.8765

Java considers everything with a decimal to be adouble. Since float takes up less memory and

holds up to 7 decimal places, you can cast 9.8765as a float.

There are better real-world examples out therethan this, especially when you get into objects

int i = (int) f //what is i?

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Java Integer Arithmetic

int a = 16, b=3, c, d;

c = a / b;d = a % b;

The result of 16/3 is 5 remainder of 1;

therefore, c = 5, d = 1

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Java Arithmetic of differing types

int a = 3;

double b = 2.0, c; //note decimal!c = a / b;

When doing this math, Java will promote thenumber with less precision to the higher

precision (i.e. int to double) to get a result ofthe higher precision (see table 2.10, pg 66)

c ends up as .75

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Increment and Decrement Operators

These provide a quick way to add or subtract

1 from a variable

i++ or ++i will add 1 to i

i-- or --i will subtract 1 from i

When assigning values, there is a difference

between i++ and ++i (see table 2.12 p70)

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Accumulation Operators

Operator Example Result

+= sum += x sum = sum + x

-= sum -= x sum = sum x

*= sum *= x sum = sum * x

/= sum /= x sum = sum / x

Note that you dont NEED to use

accumulation operators, but they are a nice

shorthand.