Download lec1!Introduction

Java Programming
Introduction to
Java Programming
Cheng-Chia Chen
Feburary 2013
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Java Programming
Course web page
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Java Programming
Lecture 1. Introduction
Cheng-Chia Chen
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Java Programming
Contents
1.
2.
3.
4.
5.
What is Java?
Features of Java
Evolution of Java
Develop first Java program
Structure of java code
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What is Java?
Java Programming
Java is
 a programming language,
 defined in The Java language specification (v1,v2,v3, se7)
 a virtual machine,
 Defined in The java virtual machine (v1, v2, se7)
 Many languages can be compiled into JVM code.
 Java code can also be compiled into non-jvm code:
 Android: java  Dalvik VM
 a platform
 Standard edition (j2se 7.0 java se 7):
 Java platform, standard edition 7
 Enterprise edition(j2ee 5.0  java ee 5):
 Java platform, enterprise edition 6 (for enterprise-class
service-oriented architecture (SOA) and web applications.)
 Micro edition (j2me  java me): Java Platform,
 Micro edition (for mobile&embeded devices)
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servers & enterprise computers
Java Programming
Desktop & personal computers
High-end consumer devices
Low-end devices
J2ME
smartcards
Java 2 Platform editions and their target markets
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Java Programming
 Java SE 7 Platform at a Glance
 Java SE 6 Platform at a Glance
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Java Programming
Features of the java language:
Java is
 simple
 object-oriented
 distributed
 interpreted
 robust
 secure
 architecture-neutral
 portable
 high performance
 multithreaded
 dynamic
reference
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Java Programming
Java is Simple
 Intentionally created to be syntactically similar to C/C++
 Eliminate traditionally troublesome features of C/C++
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Pointer arithmetic (no troublesome * and &)
Multiple inheritance
Implicit type coercions // if (1) {x = 1 ;} is not well-formed
Explicit memory management
Preprocessor
 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
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Java Programming
Java is 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.
 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(
封裝), inheritance(繼承), and polymorphism(多型).
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Java Programming
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 funcition invocation)
 (In java) everything is part of a class
 Supported OO Concepts:
 Data abstraction and Encapsulation
 Inheritance
 Polymorphism
 dynamic binding - overriding
 overloading
Non-OO
 generics
features
 Logical cluster of classes == package
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Java Programming
Java is a Distributed language
 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.
 Network programming support built into JDK class
library:
 TCP sockets ,UDP packets ,IP addresses
 URLs ,RMI (Remote Method Invocation)
 Web Service
 Security features designed into language
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Java Programming
Java is an Interpreted language
 Language implementation
 Compiler – produce machine code
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Ex: Fortran, Cobol, C, C++
 Interpreter – execute source or compiled
instructions on a virtual machine
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Ex: Scheme, Haskell, Python., Java
 Hybrid compilation/interpretation : Java
 The Java Virtual Machine (JVM)
 java code compile byte code (machine independent)
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[ 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).
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Java Programming
Java is Robust
 characteristics of Java
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Strongly-typed language (cf Smalltalk and VisualBasic)
Compile-time and runtime checking
No pointer arithmetic
Exception handling
Automatic memory management
 Java compilers can 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.
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Java Programming
Java is secure
 Designed with security 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.
 subjected to intense 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)
 Should update (from 7~10) to se 7 update (11-15) now.
 One of the best mainstream platforms with the
strongest security guarantee.
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Java Programming
Java is Architecture-neutral
 Byte-codes are architecture 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
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Java Programming
Java is portable (source code level)
 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."
(Core Java, page 9)
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Java Programming
High performance
 Interpreting leads to 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.
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Java Programming
Multithreaded
 Based on well-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.
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Java Programming
Dynamic
 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
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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 {… }
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Java Programming
An Example
/**
* The HelloJava class implements an application that
* simply displays "Hello Java!" to the standard output.
*/
class HelloJava {
public static void main(String[] args) {
// Display "Hello Java!"
System.out.println("Hello Java!");
}
}
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Java Programming
Early history of Java
 Green Project (1990)
 need a small PL for developing consumer device operating software
 Requirements: small size, robust, portable, extremely reliable ,realtime 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)
 Early History Website :
 http://java.sun.com/features/1998/05/birthday.html(broken)
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Java Programming
Evolution of the Java Language
• Java version History
(8 packages)
(23 packages)
java 2
(59 packages)
(76 packages)
2002
(135 packages)
(166 packages)
(202 packages)
7
2011-7/7 featureChange
•Jan, 2010: sun and java were owned by oracle.
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Java Programming
Develop your first Java Program
1. Required software
2. Creating Your First Application
a. Create a Java Source File
b. Compile the Source File
c. Run the Program
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Required Softwares
To write your first program, you will need:
1. The Java Platform, Standard Edition.
2. A text editor. Ex:
 NotePad,
 Ultraedit,
 EditPlus2
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2. Creating Your First Application
 The first program, HelloWorldApp, will simply
display : “Hello World!".
 Steps:
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a. Create a Java source file.
> Notepad HelloWorldApp.java
b. Compile the source file into a bytecode file.
> javac HelloWorldApp.java
c. Run the program contained in the bytecode file.
>java HelloWorldApp
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Java Programming
HelloJava.java
/**
* The HelloWorldApp class implements an application that
* simply displays "Hello World!" to the standard output.
*/
class HelloWorldApp {
public static void main(String[] args) {
// Display "Hello World!"
System.out.println("Hello World!");
}
}
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Java Programming
Java Jargon
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Java Programming
Java 2 SDK Installation Instructions (for WIN32)
1. Download java SDK standard edition
2. Run the Java SDK executable (*.exe).
 determine where to install java se. (ex: c:\java\jdk7)
 > set JAVA_HOME= c:\java\jdk7
3. Update the PATH variable
 so that you can type ‘java’ instead of ‘c:\java\jdk7\bin\java’ to invoke java tools.
 > path=%JAVA_HOME%\bin;%PATH%
4. Check the CLASSPATH variable
 Used by java tools to determine where to find your personal (nonsystem) java class
files
 Types of java byte codes (class files):
 System : java tools know where to find them.
 Extensions: put in %JAVA_HOME%\jre\lib\ext
 Personal: via CLASSPATH or –cp/–classpath options
5. Start using the Java SDK tools!
 java, javac, javadoc, jdb, javap,…
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Java Programming
Create Your first Java application using Eclipse IDE
 install Eclipse SDK
 Download Eclipse SDK (choose Classic)
 unzip to a dir (c://eclipse)
 Start Eclipse
 go to c:\eclipse
 run eclipse.exe
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choose Java perspective
create a java project ( helloWorld )
create a package chapter1 using package widard
create HelloWorld class using class wizard
run HelloWorld class
 Reference: Eclipse Tutorial | One-Page Startup Instruction
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Java Programming
How java code are 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 ).
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Java Programming
Package and class naming
 A class or package has two names:
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simpleName
fully qualified name = parentPackageName . simpleName
packageName = parentPackageName . simpleName
For package, we use only its full name.
 Ex:
 java.lang.String
 javax.swing.JButton
 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.
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CLASSPATH: Where to find java class and source
Java Programming
 How does java/javac find a class or src x.y.z.A in the
package x.y.z ?
 Notes:
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 package x.y.z is a subpackage of x.y, which is a
subpackage of x.
 we called package x, java, javax etc, top-level packages.
 java find the location of top-level packages from a list of
directory(package roots) given by a system variable
called CLASSPATH.
Ex: If CLASSPATH = d:\my\root;. Then
package x is mapped to dir d:\my\root\x or ./x
package x.y is mapped to dir d:\my\root\x\y or ./x/y
package x.y.z => d:\my\root\x\y\z or ./x/y/z
class or src x.y.z.A => d:\my\root\x\y\z\A.class or
d:\my\root\x\y\z\A.java or …
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