A Java introduction SDK, FC 15/12/2009 UMR AMAP. SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

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1 A Java introduction SDK, FC UMR AMAP 15/12/2009 SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

2 Plan 1 Introduction 2 Bases Java Application Variables & Expressions Simple Arrays Exceptions Collections Control structure Functions 3 Objects Classes Inheritance Polymorphism 4 Java standard library 5 To go further SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

3 History James Gosling and Sun Microsystems Java, May 20, 1995 Java 1 Java 6 GPL with classpath exception since 2006 SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

4 Characteristics Object Oriented Interpreted (need a virtual machine) Portable (Linux, Mac, Windows) Dynamic (introspection) Static typing (checks during compilation) Simplier than C++ (memory management, pointers, headers...) SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

5 Programming environment Java Environnment JRE (Java runtime environment) JDK (Java Development Kit) Jave SE (Standard edition) Java EE (Enterprise edition Web) Java ME (Micro edition) IDE - Editor Eclipse, NetBeans : Full IDE (completion, compilation...) Simple Editors : Notepad++, TextPad, Scite (coloration, indentation) SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

6 Installation Windows Download and install the last JDK (Java SE 6) Environment variable (Computer properties) Add to PATH variable the bin directory eg : C :/Program Files/Java/jdk1.6.0 version/bin Install editor TextPad or Notepad++ Linux sudo apt-get install sun-java6-jdk sudo apt-get remove openjdk-6-jdk Editor : use scite or gedit SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

7 Java application Java programs written in files with extension.java Applications are.java files with public static void main(...) method Compile and run Java application Run the compiler on a.java file : javac package/myprogram.java Produce a file of Java byte code : MyProgram.class Run the interperter on a.class file : java package.myprogram the tools javac java are part of the JDK SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

8 Workflow SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

9 Hello world package h e l l o ; / A p p l i c a t i o n H e l l o w o r l d / p u b l i c c l a s s H e l l o W o r l d { / Main Funcion / s t a t i c p u b l i c v o i d main ( S t r i n g [ ] a r g s ) { // p r i n t to s c r e e n System. out. p r i n t l n ( " Hello world!" ) ; Print to console : System.out.println( a string ) ; Commands finish with a ; Comments : // or /* */ Package : hello = directory java hello.helloworld SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

10 Create a new application Copy directory Rename directory and file : class Name and file name should be identical The package is a namespace and corresponds to the directories package name and directory should be identical Exercice : Create a new application package1.app1 SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

11 Variable & Simple type Variable A variable has a type and hold a value or an Object A variable name starts with lowercase, eg : myvariable ; boolean : true or false int : signed integer 32 bits long : signed integer 64 bits float : floating point 32 bits double : floating point 64 bits Object : a generic object initialization by default : 0 int avariable = 2 ; float anothervariable = 3.56f ; Use final for constants : final float CONSTANT = 0.1f ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

12 Operators Arithmetic +, -, *, /, % myint++, otherint ; +=, -=, *=, /=... Precedence : use parenthesis () division 2 / 3 different of 2.0 / 3.0 Division par zero Infinity or NaN Exercise : arithmetic.dividebyzero SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

13 Math import java.lang.math Constante : Math.PI, Math.E Math.abs(), Math.pow(), Math.sqrt(), Math.exp(), Math.log(), Math.cos(), Math.tan()... Math.toDegrees(), Math.toRadians() Javadoc : Java Math Exercice : Calculate triangle hypothenus with pythagore SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

14 Simple Arrays One or 2 dimensions arrays Dynamic allocation : new keyword null if not initialized Not resizable Access with [] operator Index begin at 0 S t r i n g [ ] a r r a y 1 a = new S t r i n g [ 1 2 ] ; S t r i n g [ ] a r r a y 1 b = {" toto ", " tata ", " titi " ; i n t s i z e = 4 ; double [ ] a r r a y 1 c = new double [ s i z e ] ; double [ ] [ ] a r r a y 2 = new double [ 4 ] [ 6 ] ; a r r a y 1 a [ 1 1 ] = "a string " ; a r r a y 2 [ 0 ] [ 2 ] = 3d ; a r r a y 2 [ 3 ] [ 5 ] = 1d ; System. out. p r i n t l n ( a r r a y 2 [ 4 ] [ 6 ] ) ; // i n d e x e r r o r SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

15 Error during execution Try to use an object not initialized Try to acces to a non exisiting element in array double [ ] a r r a y = n u l l ; System. out. p r i n t l n ( a r r a y. l e n g t h ) ; a r r a y = new double [ 1 0 ] ; System. out. p r i n t l n ( a r r a y [ 1 0 ] ) ; Exceptions are raised and stop the program SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

16 Exceptions Error can be catched anywhere in the program Specific exceptions can be raised double [ ] a r r a y = n u l l ; t r y { System. out. p r i n t l n ( a r r a y. l e n g t h ) ; catch ( E x c e p t i o n e ) { System. e r r. p r i n t l n ( e ) ; t r y { double r e s u l t = a r r a y [ 1 0 ] ; catch ( E x c e p t i o n e ) { r e s u l t = 0. ; System. out. p r i n t l n ( " Result : " + r e s u l t ) ; // i f ( r e s u l t < 0) { throw new E x c e p t i o n ( r e s u l t cannot be n e g a t i v e ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

17 Complex types Java manipulates Objects An object is a concept (e.g a particular data structure) Objects are instantiated with the keyword new A variable contains a reference to an object Affectation is a reference copy (the variable point to the same object) Objects are destroyed when there is no reference on it By default an object variable is set to null Objects have properties and methods accessible with the. operator MyObject o1, o2 ; // n u l l ; o1 = new MyObject ( ) ; o1. v a l u e ; o1. sum ( ) ; o2 = o1 ; o1 = n u l l ; o2 = n u l l ; // O bject w i l l be d e s t r o y e d by t h e garbage c o l l e c t o r SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

18 Collections Collections are dynamic containers Associated to a specific type Specific behaviour : list, set, map.. Simple types (int, float, double...) are not objects need a wrapper int Integer float Float double Double Collection class has method to sort, shuffle, reverse,... collections See javadoc : Collection java 1.6 C o l l e c t i o n <S t r i n g> c1 ; C o l l e c t i o n <I n t e g e r > c2 ; C o l l e c t i o n <Double> c2 ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

19 ArrayList An ordered collection of variable size Growth automatically get, add and set method Insertion is slow For a stack or a queue, use LinkedList List<String> l = new ArrayList<String >(); l. add ( " toto " ) ; l. add ( " tata " ) ; l. add ( " titi ", 1 ) ; // i n s e r t a t i n d e x 1 l. s e t ( 1, " tutu " ) ; // r e p l a c e a t i n d e x 1 l. s i z e ( ) ; // 3 l. g e t ( 0 ) ; // t o t o... SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

20 HashSet An unordered collection without duplicated elements contains method is fast Set<String> s = new HashSet<String >(); s. add ( " toto " ) ; s. add ( " tata " ) ; s. add ( " titi " ) ; s. add ( " toto " ) ; // f a l s e s. s i z e ( ) ; // 3 s. c o n t a i n s ( " tutu " ) ; // f a l s e... SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

21 HashMap Map associate a key with an object a key should be unique (like in a Set) Map<String, Color> m = new HashMap<String, Color >(); m. put ( " black ", new C o l o r ( 0, 0, 0 ) ) ; m. put ( " red ", new C o l o r ( 1, 0, 0 ) ) ; m. put ( " green ", new C o l o r ( 0, 1, 0 ) ) ; m. put ( " blue ", new C o l o r ( 0, 0, 1 ) ) ; m. g e t ( " red " ) ; // r e t u r n a c o l o r o b j e c t m. c o n t a i n s K e y ( " black " ) ; // t r u e m. k e y S e t ( ) ; // s e t o f k e y s SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

22 Boolean arithmetic boolean v = true ;! && <= >= < > ==!= == and equals() : reference vs contents!= and!equals() use () for precedence SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

23 if else Simple condition Can be combined // s i m p l e i f i f ( c o n d i t i o n ) { b l o c k // complex i f i f ( c o n d i t i o n ) { b l o c k 1 e l s e i f ( o t h e r c o n d i t i o n ) { b l o c k 2 e l s e { b l o c k 3 i f ( v1 &&! v2 ) { System. out. p r i n t l n ( "v1 and not v2" ) ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

24 while Loop with condition i n t c o u n t e r = 0 ; w h i l e ( c o u n t e r < 100 ) { System. out. p r i n t l n ( " counter : " + c o u n t e r ) ; c o u n t e r ++; i n t c o u n t e r 2 = 0 ; i n t sum = 0 ; w h i l e ( c o u n t e r 2 < 100) { sum += Math. random ( ) ; i f ( sum > 20) { break ; c o u n t e r += 1 ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

25 for Loop with index // With an a r r a y i n t [ ] a r r a y = new a r r a y [ 1 2 ] ; i n t sum = 0 ; f o r ( i n t i =0; i<a r r a y. l e n g t h ; i ++) { sum += a r r a y [ i ] ; Loop in a collection // With a l i s t List<Integer> l = new ArrayList<Integer >(); i n t sum = 0 ; f o r ( I n t e g e r v : l ) { sum += v ; // With a Map Map<String, Object> m = new HashMap<String, Object >(); f o r ( S t r i n g key : m. k e y S e t ( ) ) { System. out. p r i n t l n (m. g e t ( key ) ) ; Exercice : do the sum of a double array SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

26 Enumeration A enumeration is a type with a limited number of value Type checking Better than using integer or constante values // Type d e c l a r a t i o n enum StopLight {red, amber, green ; // Use t y p e StopLigth s ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

27 static Functions Like a mathematical function Reuse a block of code Inputs Parameters : type + variable name Output : return type s t a t i c double afunction ( double param1, double param2 ) { r e t u r n param1 param1 + param2 ; param1 and param2 are the parameters their names have a local scope : they are only available in the function double a = 2 ; double b = 3 ; double r e s u l t = a F u n c t i o n ( a, b ) ; // a F u n c t i o n ( 2, 3 ) System. out. p r i n t l n ( r e s u l t ) ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

28 Functions (2) a class can contain several functions if no parameters use () if no return type use void p u b l i c c l a s s MyClass { public s t a t i c double function1 ( double param1, double param2 ) {... p u b l i c s t a t i c v o i d f u n c t i o n 2 ( ) {... p u b l i c s t a t i c v o i d main ( S t r i n g [ ] a r g s ) {... SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

29 Read a file Scanner tool parses a list of token import j a v a. u t i l. Scanner ;... // i n a f u n c t i o n Scanner sc = new Scanner (new F i l e ( " filename.txt " ) ) ; w h i l e ( s c. hasnext ( ) ) { S t r i n g s = s c. n e x t ( ) ; // r e a d a s t r i n g i n t i = s c. n e x t I n t ( ) ; // r e a d an i n t f l o a t f = s c. n e x t F l o a t ( ) ; // r e a d a f l o a t // Read i n t h e s h e l l Scanner sc2 = new Scanner ( System. in ) ; System. out. p r i n t ( " Input a string : " ) ; S t r i n g s = s c 2. n e x t ( ) ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

30 Exercices Create a file with a list of number : numbers.txt Create a application which read the file in an ArrayList of Float ArrayList<Float> Compute the mean (and the variance) of the data Put the code in a function Use args argument in main to pass the filename in the command line Use the function to compute the mean for multiple files Try to put strings in the file and recover it Remove minimal and maximal values in the mean... SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

31 Object Oriented programming Java manipulates Objects E.g : a list, a number, a car, a species, a plant, a plot... Concepts Class : a type of object Instance : a real object Instance data : the data an object contains Data are different for each instanciated object Methods : the functions associated to an object SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

32 How to use Object Object are instanciated with the new keyword We can instantiate several objects of the same type Tree t1 = new Tree ( " Spruce " ) ; // i n i t i a l i z a t i o n w i t h p a r a m e t e r Tree t2 = new Tree ( " Larch " ) ; Tree t3 = new Tree ( "Fir " ) ; // each insta nce has i t s own data t1. getspeciesname ( ) ; // Spruce t2. getspeciesname ( ) ; // Larch t3. getspeciesname ( ) ; // F i r // P r o p e r t i e s t3. h e i g h t = 2 ; System. out. p r i n t l n ( t1. h e i g h t ) ; // Methods t2. setspeciesname ( " Spruce " ) ; // t2!= t1 but t2. e q u a l s ( t1 ) // a f f e c t a t i o n t3 = t1 ; // t3 and t1 p o i n t to t h e same o b j e c t t3 == t1 t3. getspeciesname ( ) ; // Spruce SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

33 Class A class is a type description It contains data and methods (members) p u b l i c c l a s s Tree { p u b l i c double height ; p r i v a t e S t r i n g speciesname ; // C o n s t r u c t o r s p u b l i c Tree ( String n ) { speciesname = n ; // A c c e s s o r s p u b l i c v o i d setspeciesname ( String n ) { speciesname = n ; p u b l i c S t r i n g getspeciesname ( ) { r e t u r n speciesname ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

34 Class... Access control Public : no access restriction Private : only accessible in the class method Protected : accessible in the class methods and in the subclasses Constructor Called when the object is created Can take parameters or not Can be declined in different versions No return type SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

35 Exercices tree/tree.java Add a private data : diameter Add corresponding accessor Add a method which return the volume of the trunk (we consider a cylinder) Create an application which use this class and this function SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

36 This this keyword represents the current object Usefull if there is ambiguity with the names p u b l i c c l a s s Tree {... / Volume o f t h e t r u n k / p u b l i c double getvolume ( ) { double volume ; double r a d i u s = t h i s. d i a m e t e r / 2d ; volume = r a d i u s r a d i u s 2d Math. PI t h i s. h e i g h t ; r e t u r n volume ; ;... SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

37 static static members are associated to the type static datas are shared by all instance static methods are not attached to an instance c l a s s Tree {... s t a t i c p u b l i c i n t s h a r e d s t a t i c public double g e t S u r f a c e ( double d i a m e t e r ) { double r a d i u s = d i a m e t e r / 2d ; double s u r f a c e = r a d i u s r a d i u s 2d Math. PI ; r e t u r n s u r f a c e ;... Tree. g e t S u r f a c e ( 2. ) Tree. s h a r e d SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

38 Inheritance We can reuse a class to make more specific classes e.g : a tree with crown, a tree with leaves, etc... Inheritance corresponds to a is a relation A sub-class has all the data and methods of its parent All class inherit from the class Object Multiple inheritance is not allowed SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

39 Inheritance // Tree. j a v a c l a s s Tree { // e x t e n d s O b ject p r o t e c t e d double height ; / C o n s t r u c t o r / p u b l i c Tree ( double h ) { h e i g h t = h ; p u b l i c double getheight ( ) ; // CrownTree. j a v a c l a s s CrownTree extends Tree { p r o t e c t e d double crownheigth ; p r o t e c t e d double crowndiameter ; / C o n s t r u c t o r / p u b l i c CrownTree ( double h, double ch, double cd ) { s u p e r ( h ) ; // p a r e n t c o n s t r u c t o r crownheigth = ch ; crowndiameter = cd ; p u b l i c double getcrownvolume ( ) {... SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

40 instanceof All class inherit from Object instanceof tests the type of an object Tree t = new Tree (10d ) ; CrownTree ct = new CrownTree (10d, 4d, 4d ) ; c t i n s t a n c e o f CrownTree ; // t r u e c t i n s t a n c e o f Tree ; // t r u e ct i n s t a n c e o f Object ; // t r u e t i n s t a n c e o f Tree ; // t r u e t i n s t a n c e o f CrownTree ; // f a l s e SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

41 Cast We can use the parent type in the code ( is a relation) we use a cast, when we have to change the type to a subtype a cast can fail Tree t1 = new Tree (10d ) ; Tree t2 = new CrownTree (10d, 4d, 4d ) ; t1. getcrownvolume ( ) ; // f a i l : not a c r o w n t r e e t2. getcrownvolume ( ) ; // f a i l : j a v a t h i n k i t i s a Tree CrownTree ct1 = ( CrownTree ) t2 ; // ok c t 1. getcrownvolume ( ) ; // ok CrownTree ct1 = ( CrownTree ) t1 ; // f a i l : t1 i s not a CrownTree SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

42 Override Method can be overriden in sub-class Use c l a s s Tree { / Tree growth / public void growth ( i n t nbyear ) { diameter += nbyear dbhinc ; / Tree w i t h crown / c l a s s CrownTree extends Tree { / Tree growth / public void growth ( i n t nbyear ) { s u p e r. growth ( nbyear ) ; crowndiameter += nbyear crowninc ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

43 Interface An interface is a kind of contract A class can implement several interface (multiple inheritance) An interface do not provide any implementation An interface is a type // Growthable. j a v a i n t e r f a c e Growthable { p u b l i c v o i d growth ( i n t n b y e a r ) ; // Tree. j a v a c l a s s Tree implements Growthable, Cloneable { public void growth ( i n t nbyear ) { // do growth p u b l i c Object c l o n e ( ) { // do c l o n e Growthable g = new Tree (... ) ; g. growth ( 1 0 ) ; g. g e t D i a m e t e r ( ) ; // e r r o r : j a v a don t know i f i t i s a Tree SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

44 Abstract class An abstract class is an incomplete class It cannot be instantiated Like an interface but with some implementation Can be useful to share common methods in an inheritance graph c l a s s abstract A b s t r a c t T r e e { p r i v a t e double height ; p r i v a t e double diameter ; p u b l i c double getvolume ( ) { double volume ; double r a d i u s = t h i s. d i a m e t e r / 2d ; r e t u r n = r a d i u s r a d i u s 2d Math. PI t h i s. h e i g h t ; a b s t r a c t i n t getnbleaves ( ) ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

45 Abstract class Each sub-class implements abstract methods c l a s s TreeWithNbLeaves extends A b s t r a c t T r e e { private i n t nbleaves O v e r r i d e i n t getnbleaves ( ) { r e t u r n nbleaves ; c l a s s T r e e W i t h L i s t O f L e a v e s extends A b s t r a c t T r e e { p r i v a t e L i s t <Leaf> l e a v e s O v e r r i d e i n t getnbleaves ( ) { r e t u r n l e a v e s. s i z e ( ) ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

46 Polymorphism Polymorphism means that we can use an object without knowing its exact type The correct function will be called List<AbstractTree> l = new ArrayList<AbstractTree >(); l. add ( new TreeWithNbLeaves ( ) ) ; l. add (new TreeWithListOfLeaves ( ) ) ; f o r ( AbstractTree t : l ) { System. out. p r i n t l n ( "nb leaves : " + t. getnbleaves ( ) ) ; SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

47 Exercices In the tree package Create the sub-class CrownTree Add a method to compule the volume of the CrownTree Create 2 sub-classes SphericTree and ConicTree Override the volume function Create a class Forest containing a list of trees Add function to build a random forest Compute the volume of the forest SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

48 Java library See javadoc : http ://java.sun.com/javase/6/docs/api/ GUI Math Data Structure (Collections) Input Output Networking MultiThreading Database Intropection SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

49 Apache commons libraries See web : http ://commons.apache.org/ Math IO Loggin CLI Collections... SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50

50 Some links Sun s tutorials : http ://java.sun.com/docs/books/tutorial/ Coding conventions : http ://java.sun.com/docs/codeconv/html/codeconvtoc.doc.html Resources on Capsis web site : http ://capsis.cirad.fr Millions of books... SDK, FC (UMR AMAP) A Java introduction 15/12/ / 50