Introduction to JAVA

Introduction to JAVA

• 1.
  Introduction to JAVA Md.Tanvir Hossain Student, Dept of CSE Daffodil International University 1
• 2.
  Features of Java: Simple  Intentionally created to be syntactically similar to C/C++  Eliminate traditionally troublesome features of C/C++ • Pointer arithmetic (no troublesome * and &) • Multiple inheritance • Implicit type coercions // if (1) {x = 1 ;} is not well-formed • Explicit memory management • Preprocessor 2
• 3.
  Features of Java: Simple  Eliminate features of C/C++ • struct, typedef,union • generic, enum (both recovered since jdk5.0) • (Programmer controlled) operator overloading (but preserving method overloading)  Features included as part of base language: • Threads • Exception handling • reflection 3
• 4.
  Features of Java: Object Oriented  Java is inherently object-oriented. • Although many object-oriented languages began strictly as procedural languages, Java was designed from the start to be object-oriented.  Object-oriented programming (OOP) is a popular programming approach that is replacing traditional procedural programming techniques. 4
• 5.
  Features of Java:Object Oriented  One of the central issues in software development is how to reuse code. • Object-oriented programming provides great flexibility, modularity, clarity, and reusability through encapsulation, inheritance, and polymorphism. 5
• 6.
  What is object-oriented?  Systems are built from sets of classes  Classes are instantiated at runtime to give objects  Objects communicate via messages passing (i.e., method or function invocation)  (In java) everything is part of a class 6
• 7.
   Supported OOConcepts: • Data abstraction and Encapsulation • Inheritance • Polymorphism – dynamic binding - overriding – overloading – generics  Logical cluster of classes == package 7 Features of Java: Object Oriented
• 8.
  Features of Java: Distributed  Distributed computing involves several computers working together on a network.  Java is designed to make distributed computing easy.  Since networking capability is inherently integrated into Java, writing network programs is like sending and receiving data to and from a file. 8
• 9.
  Features of Java: Distributed  Network programming is supported by built in JDK class library: • TCP sockets ,UDP packets ,IP addresses • URLs ,RMI (Remote Method Invocation) • Web Service  Security features designed into language 9
• 10.
   Language implementation •Compiler – produce machine code – Ex: Fortran, Cobol, C, C++ • Interpreter – execute source or compiled instructions on a virtual machine – Ex: Scheme, Haskell, Python., Java  Hybrid compilation/interpretation : Java 10 Features of Java : Interpreted Language
• 11.
   The JavaVirtual Machine (JVM) java code byte code (machine independent) [ just-in-time compilation native code ] execution  We need an interpreter(JVM) to run Java programs. • The bytecode is machine-independent and can be executed on any machine that has a Java interpreter, which is the Java Virtual Machine (JVM). 11 Features of Java : Interpreted Language compile
• 12.
   characteristics ofJava • Strongly-typed language (cf Smalltalk and VisualBasic) • Compile-time and runtime checking • No pointer arithmetic • Exception handling • Automatic memory management 12 Features of Java : Robust
• 13.
   Java compilerscan detect many problems that would first show up at execution time in other languages.  Java eliminated certain types of error-prone programming constructs found in other languages.  Runtime exception-handling feature provides programming support for robustness. 13 Features of Java : Robust
• 14.
   Designed withsecurity in mind. • Java implements several security mechanisms to protect your system against harm caused by stray programs. • Allow users to download untrusted code over a network and run it in a secure environment in which it cannot do any harm.  Configurable security levels and restrictions. 14 Features of Java : Secure
• 15.
   Subjected tointense scrutiny by security experts with [potentially serious ] bugs found and fixed. • become a big news if new bugs found!! • A recent security flaw(2012/08) (0-day flaw)  One of the best mainstream platforms with the strongest security guarantee. 15 Features of Java : Secure
• 16.
   Byte-codes arearchitecture neutral • Write once, run anywhere • With a Java Virtual Machine (JVM), you can write one program that will run on any platform.  Performance suffers somewhat by using bytecodes 16 Features of Java : Architecture Neutral
• 17.
   Source code: • Primitive type sizes are explicit - not architecture dependent • Strings and characters are (16-bit) Unicode compliant – easier for internationalization.  Byte code: • run everywhere where a JVM is available  User experience : • GUI libraries give a native graphic library-independent mechanism for creating quality graphical interfaces (sort of) • "They gave us a library that is good for writing programs that look equally mediocre on the different systems." 17 Features of Java : Portable
• 18.
   Interpreting leadsto quicker development cycle  Depends what you compare it to • "Slightly faster than VB" - (Core Java, page 9) • JITC(Just-In-Time Compiler) help greatly in this respect • Sun’s Java HotSpot is Newest high performace JIT compiler.  Can use native code for mission-critical performance sections of code • JNI: Java Native Interface • Sacrifice portability. 18 Features of Java : High Performance
• 19.
   Based onwell-known 20 year old Hoare monitor synchronization  Thread support built into language  Thread synchronization primitives supplied  Garbage collector runs permanently as a low priority background thread  Issue: • Still hard to use right for general programmers: • New package java.util.concurrency and other extensions added since jdk5 allow easier and correct use of threads. 19 Features of Java : Multithreaded
• 20.
   Class linking,layout, name resolution and object references not resolved until run-time  Runtime Type Information (RTTI) available • Can check the type of objects at run-time • java.reflect.* package  Class class for dynamic instantiation • Can create objects of types unkown until runtime. String name = getSpecies(); // get a name of a class Object p = Class.forName(name).newInstance(); if(p instanceof Hen) {…} else if(p instanceof Coq) { …} else {… } 20 Features of Java : Dynamic
• 21.
   Green Project(1990) • need a small PL for developing consumer device operating software • Requirements: small size, robust, portable, extremely reliable ,real- time performance  Oak // the resulting language • Originally used C++, then realized a new language was needed • Original requirements same as for current language  Java (1993) // OAK was renamed Java • Intended market never eventuated (no technology/product sold) • WWW starting to takeoff • Language design "based on" many current OO languages (e.g., C++, Eiffel, Smalltalk, Cedar/Mesa, Objective C) • 1995/5/23 Sun launched Java  JDK 1.0 released early 1996/1/23 ( 211 classes / 8 pkgs) 21 Early history of Java
• 22.
  Evolution of theJava Language 22
• 23.
  Java Jargon 23
• 24.
  How JAVA codeare structured  A java application consists of • many packages • Some from JRE (built-ins)+ some from 3rd party + your own ]  A package consists of • 0 or more classes • 0 or more subpackages  A java source file xxx.java is called a compilation unit, which may • contain multiple java class definitions and • may be compiled into multiple java byte code (***.class ). 24
• 25.
  Package and classnaming  A class or package has two names: • simpleName • fully qualified name = parentPackageName . simpleName • packageName = parentPackageName . simpleName • For package, we use only its full name. – Ex: – java.lang.String – javax.swing.JButton 25
• 26.
  Package and classnaming  The package/subpackage/(*.class, *.java) structure is not only logically analogous to directory/ subdirectory/ file in OS file system but in fact they are stored physically in file system in this way. • Namely, if package p is located in a directory d then subpackage p.q of p would be stored in subdirecty q of d, and class p.A of p would be stored in file named A.class or A.java. 26