Overview of Java

Mobile Website Development
Overview of Java
Facilitated by:
Michael Wakahe
Tawi Commercial
Services Ltd
Jul 2011

Table of Contents
 Introduction
 Data Types and Operators
 Program Control Statements
 Methods, Classes & Objects
 Other Topics
 Exercise
Copyright © Tawi Commercial Services Ltd. 2015. All Rights
Reserved.

Introduction
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)
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)
Reserved.

Introduction
Can be broken down into:
 Java Card
 Micro Edition (ME)
 Standard Edition (SE)
 Enterprise Edition (EE)
Reserved.

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.");
}
}
Reserved.

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 variable
int var2; // this declares another variable
var1 = 1024; // this assigns 1024 to var1
System.out.println("var1 contains " + var1);
var2 = var1 / 2;
System.out.print("var2 contains var1 / 2: ");
System.out.println(var2);
}
}
Reserved.

Data Types
and
Operators
Reserved.

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 values
Reserved.

Type 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
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.
Reserved.

Arithmentic operator examples:
 + implies addition
 / implies division
 % implies modulus
 ++ implies increment
Reserved.

 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 to
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 AND
Reserved.

 The outcome of the relational and logical
operators is a boolean value.
 The Assignment operator: var = expression;
Reserved.

• Approximately 50 keywords are currently
defined in the Java language
• Examples: enum, true, false, null, import, do,
break, for, int
Reserved.

 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.
Reserved.

Program
Control
Statements
Reserved.

Program Control
Statements
• The if statement
• if(condition) statement;
• Example:
if(10 < 11) System.out.println("10 is less than 11");
Reserved.

Program Control
Statements
 The general form of the if, using blocks of
statements, is:
if(condition)
{
statement sequence
}
else
{
statement sequence
}
Reserved.

Program Control
Statements
• 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;
...
else
statement;
Reserved.

Program Control
Statements
• The for Loop:
• for(initialization; condition; iteration) statement;
• Example
for(count = 0; count < 5; count = count+1)
System.out.println("This is count: " + count);
Reserved.

Program Control
Statements
• The Switch statement:
switch(expression) {
case constant1:
statement sequence
break;
case constant2:
statement sequence
break;
case constant3:
statement sequence
break;
...
default:
statement sequence
}
Reserved.

Program Control
Statements
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");
}
Reserved.

Program Control
Statements
 The general form of the while loop is:
while(condition) statement;
 Example:
// print the alphabet using a while loop
char ch;
ch = 'a';
while(ch <= 'z') {
System.out.print(ch);
ch++;
}
Reserved.

Program Control
Statements
• The general form of the do-while loop is
do {
statements;
} while(condition);
• Very similar to while loop
Reserved.

Methods,
Classes &
Objects
Reserved.

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
Reserved.

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
Reserved.

Classes & Objects
• The general form of a class definition:
class classname {
// declare instance variables
type var1;
type var2;
// ...
type varN;
// declare methods
type method1(parameters) {
// body of method
}
type method2(parameters) {
// body of method
}
// ...
type methodN(parameters) {
// body of method
}
}
Reserved.

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
}
Reserved.

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;
}
}
Reserved.

Overview of Java

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