1. Introduction to Java Programming

2. Key Benefits of Java Java is “write once, run anywhere”
architecture neutral
portable across different platforms
Due to Java Virtual Machine (JVM)
Security features
highly configurable security levels prevent any piece of Java code doing harm to the host system

3. Key Benefits of Java Network-centric platform Object Oriented
easy to work with resources across a network and to create network based applications
Object Oriented
an interacting collection of independent software components
dynamic extensible programs

4. Key Benefits of Java Internationalisation Performance
uses 16 bit Unicode characters that represents the phonetic and ideographic character sets of the entire world
Performance
although an interpreted language Java programs run almost as fast as native C, C++ programs
Simple and easy to develop
powerful & well designed set of APIs

5. JVM Compiled by Java compiler Interpreted by JVM myCode.class Bytecode …
myCode.class
Bytecode
Compiled by
Java compiler
class myCode { …
… }
myCode.java
Interpreted by JVM
Source Code
Application runs

6. JVM
JVM provides the run time environment for the bytecode (Java Runtime Environment JRE)
executes the bytecode and causes native machine code instructions to execute on the CPU that the JVM is on
 each target platform needs an implementation of the JVM

7. Basic Program structure
Basic class definition class className {
// field declarations … // method declarations … }
Each program needs a main method to tell the program where to start executing

8. Simple Java Program public class HelloWorld{ // no fields
accessible to all classes (info hiding)
Simple Java Program
public class HelloWorld{
// no fields
// main method public static void main (String [] args){
System.out.println("Hello World.."); } }
command line args
indicates class method
returns nothing
invoking a member

9. Objects An object includes state (fields) and behaviour (methods)
A class object is the blueprint for the instance objects
All code must be included in a class
no inline functions like C++

10. reference to the object itself
An Example Class
a business class
predefined Java class
public class Student {
// member fields String name;
// constructor public Student(String name) {
this.name=name; }
// methods
void printDetails(){
System.out.println("\nName: “ + name); } }
no return type
reference to the object itself
String concatenation

11. Instantiation Class definition creates “class object” at runtime
To instantiate “instance objects” use new operator
ClassName myInstance = new ClassName();
where ClassName() is a constructor
Note: no need to allocate the memory for the object like in C++

12. Using a Class in a Program
the program control class
source file called myProg.java
public class myProg {
public static void main(String args []){
// instantiate a Student object Student student= new Student("Joe Bloggs");
// invoke printDetails method student.printDetails();
} }
case sensitive

13. Using the JDK Create source files for each class in your program
The name of source file should be the same as the name of class
public class myCode { …
… }
myCode.java
Source File

14. Compiling your source code
Compile each class source file into bytecode (class files)
To compile a java source file
javac myCode.java
This creates a classfile called myCode.class …
myCode.class
Class File

15. To run your program
To start your program running you run the bytecode of the program control class
The program control class has the main method
To run bytecode – pass it to the JVM
java classFileName
e.g. java myProg note no .class included