Overview of Java

Mobile Website DevelopmentOverview of Java

Facilitated by:Michael WakaheTawi Commercial Services LtdJul 2011

Table of Contents

Introduction

Data Types and Operators

Program Control Statements

Methods, Classes & Objects

Other Topics

ExerciseCopyright © Tawi Commercial Services Ltd. 2015. All Rights

Reserved.

Introduction

Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.

Introduction

Originally developed by James Gosling at Sun

Microsystems - 1991

Derives much of its syntax from C and C++

Applications are typically compiled to

bytecode (class file) that can run on any Java

Virtual Machine (JVM) Copyright © Tawi Commercial Services Ltd. 2015. All Rights

Reserved.

Introduction

Is a general-purpose, concurrent, class-based,

object-oriented language

“Write once, run anywhere"

Current stable release: Java Standard Edition 6

(1.6.0)


Introduction


Introduction

Can be broken down into:

Java Card

Micro Edition (ME)

Standard Edition (SE)

Enterprise Edition (EE)


Introduction/*

This is a simple Java program.Call this file Example.java. Compile and run in Eclipse.

*/class Example {

// A Java program begins with a call to main().public static void main(String args[]) {

System.out.println("Java drives the Web.");}

}


Introduction/*This demonstrates a variable.Call this file Example2.java. Compile and run in Eclipse.*/class Example2 {

public static void main(String args[]) {int var1; // this declares a variableint var2; // this declares another variablevar1 = 1024; // this assigns 1024 to var1System.out.println("var1 contains " + var1);var2 = var1 / 2;System.out.print("var2 contains var1 / 2: ");System.out.println(var2);

}}


Data Types and

Operators



• Contains 2 general categories of built-in data

types: object-oriented and non-object

oriented.

• There are eight primitives

• Primitive means these types are not objects

but rather normal binary valuesCopyright © Tawi Commercial Services Ltd. 2015. All Rights

Reserved.

Data Types and OperatorsType Meaning

boolean Represents true/false values

byte 8-bit integer

char Character

double Double-precision floating point

float Single-precision floating point

int Integer

long Long integer

short Short integer



• Contains 2 general categories of built-in data

types: object-oriented and non-object

oriented.

• There are eight primitives

• Primitive means these types are not objects

but rather normal binary valuesCopyright © Tawi Commercial Services Ltd. 2015. All Rights

Reserved.


• An operator is a symbol that tells the compiler

to perform a specific mathematical or logical

manipulation.

• Java has four general classes of operators:

arithmetic, bitwise, relational, and logical.



Arithmentic operator examples:

+ implies addition

/ implies division

% implies modulus

++ implies increment



Relational refers to the relationships that values can have with one another

Examples include:

== implies Equal to

!= implies Not Equal to

> implies Greater than

<= implies Less than or Equal toCopyright © Tawi Commercial Services Ltd. 2015. All Rights

Reserved.


Logical refers to the ways in which true and false values can be connected together

Examples include:

& implies AND

| implies OR

! implies NOT

&& implies Short-circuit ANDCopyright © Tawi Commercial Services Ltd. 2015. All Rights

Reserved.


The outcome of the relational and logical

operators is a boolean value.

The Assignment operator: var = expression;



• Approximately 50 keywords are currently

defined in the Java language

• Examples: enum, true, false, null, import, do,

break, for, int



An identifier is a name given to a method, a

variable, or any other user-defined item Identifiers can be from one to several

characters long Variable names may start with any letter of

the alphabet, an underscore, or a dollar sign.


Program Control

Statements



• The if statement

• if(condition) statement;

• Example:

if(10 < 11) System.out.println("10 is less than 11");



The general form of the if, using blocks of statements, is:if(condition){statement sequence}else{statement sequence}



• A common programming construct that is based upon the nested if is the if-else-if ladder.

if(condition)statement;

else if(condition)statement;

else if(condition)statement;

...elsestatement;



• The for Loop:

• for(initialization; condition; iteration) statement;

• Example

for(count = 0; count < 5; count = count+1)

System.out.println("This is count: " + count);



• The Switch statement: switch(expression) {

case constant1:statement sequencebreak;



...default:

statement sequence}



int i = …

switch(i) {case 0:

System.out.println("i is zero");break;

case 1:System.out.println("i is one");break;

case 2:System.out.println("i is two");break; break;

default:System.out.println("i is three or more");

}



The general form of the while loop is: while(condition) statement;

Example:// print the alphabet using a while loopchar ch;ch = 'a';while(ch <= 'z') {

System.out.print(ch);ch++;

}



• The general form of the do-while loop is

do {statements;

} while(condition);

• Very similar to while loop


Methods, Classes & Objects


Classes & Objects

Java’s basic unit of encapsulation is the class

A class defines the form of an object

It specifies both the data and the code that

will operate on that data


Classes & Objects

Java uses a class specification to construct

objects

Objects are instances of a class.

Thus, a class is essentially a set of plans that

specify how to build an object


Classes & Objects• The general form of a class definition:class classname {

// declare instance variablestype var1;type var2;// ...type varN;// declare methodstype method1(parameters) {

// body of method}type method2(parameters) {

// body of method}// ...type methodN(parameters) {

// body of method}

}


Classes & Objects

How objects are declared:

Classname referenceName = new

Classname(arguments); The general form of a method is:

ret-type name( parameter-list ) {// body of method

}


Classes & Objects

A constructor initializes an object when it is created.• A simple example that uses a constructor:

// A simple constructor.class MyClass {

int x;MyClass() {

x = 10;}

}


Other Topics


Other Topics

• Casting: A cast is an instruction to the

compiler to convert one type into another.

• A cast has this general form:

(target-type) expression


Other Topics

• Inheritance is the process by which one object

can acquire the properties of another object.

• Use of hierarchies.

• The inheritance mechanism that makes it

possible for one object to be a specific

instance of a more general caseCopyright © Tawi Commercial Services Ltd. 2015. All Rights

Reserved.

Other Topics

Polymorphism - “one interface, multiple

methods.”

This means that it is possible to design a

generic interface to a group of related

activities.


Other Topics

• Packages are groups of related classes.

• Packages help organize your code and provide another layer of encapsulation.

• An interface defines a set of methods that will be implemented by a class.


Other Topics

An interface does not, itself, implement any

method.

It is a purely logical construct.

Packages and interfaces give you greater

control over the organization of your program


Other Topics

An exception is an error that occurs at run

time.

Using Java’s exception handling subsystem you

can, in a structured and controlled manner,

handle run-time errors.

Use try-catch and ThrowableCopyright © Tawi Commercial Services Ltd. 2015. All Rights

Reserved.

Other Topics Java has built-in support for multithreaded

programming. A multithreaded program contains two or more

parts that can run concurrently. Each part of such a program is called a thread,

and each thread defines a separate path of execution.

Thus, multithreading is a specialized form of multitasking.


Exercise


Exercise

• Program to simulate a School

• Attributes of school include:

– Name

– Location

• School has Teacher and Students


Exercise

• Teacher has:

– First & Last Name

– Course taught

– Years employed


Exercise

• Student has:

– First & Last Name

– 5 subjects with grades

– Can get average grade

– Has a fee balace


The End

Michael [email protected]+254 (0)20 239 3052

www.tawi.mobi


mailto:[email protected]

http://www.tawi.mobi/

Education

Overview of Java