Java Tutorial 1

Java Tutorial 1

• 1.
  Objectives  Key Featuresof Java Technology  Define class and application  Writing a simple Java Application  Java Virtual Machine’s function  Garbage Collection  Code Security
• 2.
  What is theJava Technology?  A programming Language  A Development environment  An Application environment  A deployment environment
• 3.
  Primary Goals ofJava Technology  Provides an easy to use language by  Avoiding the pitfalls of other languages such as pointers, memory management etc  Object Oriented  Enable users to create streamlined and clear code  Provides an interpreted environment  Speed of development  Code Portability
• 4.
  Primary Goals (contd..) Enables users to run more than one thread  Loads classes Dynamically  Furnishes better security
• 5.
   The followingfeatures fulfill these goals  The Java Virtual Machine  Garbage Collection  Code Security
• 6.
  // TestGreeting.java // Sample"Hello World" Application public class TestGreeting{ public static void main(String[] args) { Greeting hello = new Greeting("Hello"); hello.greet("World"); } } A Basic Java Application
• 7.
  A Basic JavaApplication-Contd.. //Greeting.java public class Greeting{ private String salutation; Greeting(String s){ salutation = s; } public void greet(String whom){ System.out.println(salutation+” “+whom); } }
• 8.
  Compiling and Running Compiling TestGreeting.java javac TestGreeting.java  Greeting.java is compiled automatically  Running an application Java TestGeeting
• 9.
  The Java VirtualMachine  Provides hardware platform specifications  Reads compiled byte codes that are platform independent  Is implemented as software or hardware  Is implemented in a Java technology development tool or a web browser
• 10.
  JVM Unix DOS JavaOS TestGreeting.javaGreeting.java TestGreeting.class Greeting.class javac Also compiles JVM JVM Can run on multiple platforms java CompileRuntime
• 11.
  Garbage Collection  JavaProvides a system level thread to track memory allocation  Garbage Collection  Checks for and frees memory no longer needed  Is done automatically  Can vary across JVM implementations
• 12.
  Code Security TestGreeting.java TestGreeting.class javac Class Loader Bytecode verifier Interpreter Runtime JIT Code Generator Hardware Networ k Networ k Compile Runtime
• 13.
  Java Runtime Environment JVM Performs 3 main tasks  Loads Code – Performed by class loader  Verifies Code – Performed by bytecode verifier  Executes Code – Performed by runtime interpreter
• 14.
  Class Loader  Loadsall classes necessary for the execution of a program  Maintain classes of the local file system in separate “namespace”  Prevents spoofing
• 15.
  Bytecode Verifier  Ensuresthat  The code adheres to the JVM specification  The code does not violate system integrity  The code causes no operand stack overflows or underflows  The parameter types for al operational code are correct  No illegal data conversions have occurred
• 16.
  Object Oriented Programming
• 17.
  Objectives  Define modelingconcepts  Abstraction, encapsulation and Packages  Define class, member, attribute, method, constructor and package  Use access modifiers private and public  Invoke a method on a particular Object
• 18.
  Abstraction  Functions –Write an algorithm once to be used in many situations  Objects – Group a related set of attributes and behaviors into a class  Frameworks and API’s – Large group of objects that support a complex activity
• 19.
  Classes as Blueprintsfor Objects  A blueprint is a description from which many physical devices are constructed  A class is a description of an object  A class describes the data each object includes  A class describes the behaviors that each object exhibits  Classes support 3 key features of OOP •Encapsulation •Inheritance •Polymorphism
• 20.
  Declaring Java Classes Example public class Vehicle{ private double maxLoad; public void setMaxLoad(double val) { maxLoad=val; } }
• 21.
  Declaring Attributes  Example publicclass Foo{ public int x; private float y = 1000.0F; private String name=“Fred Smith”; }
• 22.
  Declaring Methods  Examples publicclass Thing{ private int x; public int getX(){ return x; } public void setX(int new_x){ x=new_x; } }
• 23.
  Accessing Object Members The “dot” notation <object>.<member> is used to access object members including attributes and methods  Example thing1.setX(47); thing1.x=47;
• 24.
  Information Hiding The Problem MyDate +day: int +month : int +year : int Client code has direct access to internal data MyDate d = new MyDate(); d.day=32; //invalid day d.month=2;d.day=30;//wrong d.day=d.day+1; //no check
• 25.
  Information Hiding  TheSolution: MyDate -day: int -month: int -year: int +getDay(): int +getMonth(): int +getYear(): int +setDay(d: int): boolean +setMonth(m: int) +setYear(y: int) -validDay(d: int): boolean Client code must use setters / getters to create internal data MyDate d = new MyDate(); d.setDay(32); //invalid returns false d.setMonth(2);d.setDay(30); //setDay returns false d.setDay(d.getDay()+1); //will return false if wrap occurs
• 26.
  Encapsulation  Hides implementation details Forces the user to use an interface to access data  Makes the code more maintainable MyDate -date: long +getDay(): int +getMonth(): int +getYear(): int +setDay(d: int) +setMonth(m: int) +setYear(y: int) -validDay(d: int): boolean
• 27.
  Declaring Constructors  Example publicclass Thing{ private int x; public Thing(){ x=47; } public Thing(int new_x){ x=new_x; } }
• 28.
  The Default Constructor There is always at least one constructor in every class  If no constructors are provided a default constructor will be present  The default constructor takes no arguments  The default constructor has no body  Enables you to create object instances without having to write a constructor
• 29.
  Source File Layout Example package shipping.reports.web; import shipping.domain.*; import java.util.List; import java.io.*; public class VehicleCapacityRepport{ private List vehicles; public void generateReport(Writer op){ --- } }
• 30.
  Packages  Packages helpmanage large Software Systems  Packages can contain classes and sub-packages shipping GUI reports domain Company Vehicle Truck RiverBarge
• 31.
  The package Statement Example package shipping.reports.web;  Specify the package declaration at the beginning of the source file  Only one package declaration per source file  If no package declaration is declared, the class belongs to the default package  Package names must be hierarchical and separated by dots
• 32.
  The import Statement Precedes all class declarations  Tells the compiler where to find classes to use  Examples import java.io.Writer; //Specify a class to access import java.io.*; //all classes in the package
• 33.
  Directory Layout andPackages  Packages are stored in the Directory tree containing the package name  Example shipping/ domain/ Company.class Vehicle.class RiverBarge.class Truck.class GUI/ reports/ VehicleCapacityReport.class
• 34.
  Terminology Recap  Class– The source-code blueprint for a run-time object  Object – An instance of a class  Attribute – A data element of an object AKA: data member, instance variable, data field  Method – A behavioral element of an object AKA: algorithm, function, procedure  Constructor – A method-like construct used to initialize an object  Package – A group of classes and/or sub-packages