Outline of the lecture. Composition of objects Basic types of composition Packages meaning, creation, basic Java packages Java Archives Files (JAR)

Transcription

1 Java_3 1

2 Outline of the lecture 2 Composition of objects Basic types of composition Packages meaning, creation, basic Java packages Java Archives Files (JAR)

3 Composition & Classification 3 Composition and classification are means to organize complexity in terms of hierarchies. The two terms are used id two different, but complementary, ways. Classification and composition are used to organize our knowledge. Composition: we distinguish two basic form of composition whole part composition aggregation

4 Association relationship between classes 4 Basic division of association: general (namely single sided or double sided). At single sided association only one class knows the interface of the other class, at double sided association each class knows the interface of its partner. Navigability is used to indicate direction of association. whole part association (composition, aggregation), is a special case of association, which expreses that an object of the given class contains other objects.

5 Whole Part Asociation object composition 5 composition is a type of very tight binding among objects it occurs e.g. between the tree and its leaves, among a car and its single parts such as (wheels, body, steering wheel, motor... ), wooden stickman (head, neck, hands, body, legs). aggregation (reference composition) is a free binding among objects ir occurs e.g. between computer and its peripheries.

6 Whole Part Association Composition of Objects 6 use terms: whole or composed object part (part of composed object).

7 Semantics of Composition 7 Mouse Buttons whole part kompozice Composition is a stronger form of composing of objects. No parts can exist outside the whole. Every parts belongs only to one whole.

8 Composition Summary 8 Parts belongs only to the one whole. The whole carries exclusive responsibility for exploiting all its parts it means responsibility for their creation and destroying. Supposing responsibility for parts comes into other object the whole can its parts released. If the whole is destroyed it must destroy all its parts as well.

9 Composition Example 9 Rectangle class object is composed of the Point class objects Point class objects are declared directly in the constructor in case references of the Point class are handed over into Rectangle class constructor, it is recommended to use a copy constructor Rectangle -whole -parts Point 1 2

10 public class Point { private int x; private int y; Outline Class Point 10 public Point() { this(0, 0); public Point(int x, int y) { this.x = x; this.y = y; public Point(Point b){ //copy constructor setx(b. (b.getx getx()); sety(b. (b.gety gety()); public String tostring() { String t = String.format format("%3s %4d %4s %4d","X: ", getx(), " Y: ",gety gety()); return t; public void print() { System.out out.println println("point coordinates: "+this this.tostring tostring());

11 public int getx() { return x; public void setx(int x) { this.x = x; public int gety(){ return y; public void sety(int y){ this.y = y; public void move(int dx, int dy) { x = x + dx; y = y + dy; public void setpoint(point f) { setx(f. (f.getx getx()); sety(f. (f.gety gety()); public Point getpoint(){ return new Point(this this); //return this; Outline Class Point 11

12 public class Rectangle { private Point upperleft, lowerright; // constructor declaration public Rectangle() { upperleft = new Point(); lowerright= new Point(); public Rectangle(Point a, Point b) { //upperleft upperleft= a; lowerright= b; upperleft = new Point(a); //using copy constructor lowerright = new Point(b); public void move(int dx, int dy) { upperleft.move move(dx dx,dy dy); lowerright.move move(dx dx,dy dy); Outline Class Rectangle 12

13 public String tostring() { String tx= String.format format(" ("\n%s %s %s %s"," Rectangle upperleft: ", upperleft.tostring tostring(), " lowerright: ", lowerright.tostring tostring()); return tx; public void print() { System.out out.println println(this this.tostring tostring()); public Point getupperleft(){ return upperleft; // return upperleft.getpoint getpoint(); public void setupperleft(point b){ upperleft.setpoint setpoint(b); Outline Class Rectangle 13

14 Whole & Parts Objects 14 In the whole object we work with parts objects, we do not interfere directly into inner attributes of parts but we do it through their methods correct approach: public void move(int dx, int dy) { upperleft.move(dx,dy); lowerright.move(dx,dy); mistaken approach!!! public void move(int dx, int dy) { upperleft.setx(upperleft.getx() + dx); upperleft.y = upperleft.y + dy; lowerright.sety(lowerright.getx() + dx); lowerright.y = lowerright.y + dy;

15 public class RectangleTest { public static void main(string String[] args) { Rectangle o = new Rectangle(new new Point(9, 12), new Point(-33,46)); o.print print(); Outline Class RectangleTest 15 Point LH = new Point(22,23); Point PD= new Point(100, 200); Rectangle ob = new Rectangle(LH, PD); ob.print print(); LH.move move(-100, 100,-100); 100); LH.print print(); ob.print print();

16 Graphical presentation of the Links between Rectangle and Point 16 x valuex upperleft y valuey lowerright x valuex y valuey rectangle pointa pointb

17 Semantics of Aggregation 17 Aggregation is a relation whole/part type (consisting of many partial parts). In this type of relation one object (whole) used services of the next object (part). Whole: is a dominant in the relation, control the run of the relation. Part: provide services, reacts to demands of the whole (it is passive).

18 Semantics of Aggregation 18 Computer Printer * whole part aggregation more printers can be attached to a computer but sometime none is attached a printer can be attached maximally to a one computer or none (by the diagram) given printer can be sequentially used by more computer a printer is actually independent on the computer

19 Aggregation Summary 19 The whole used to be dependent on its parts but it can also exists independently on them (and it also exists) Parts can exist independently on the whole If some parts are missing the whole is in some sense incomplete. Parts can be shared by more wholes.

20 Aggregation and Composition Complex Example 20 There is an aggregation between Person and its Account (connection is created by set method not in constructor) There is a composition between Person and Address. The connection is created already in a constructor. Person is a whole, Address and Account are parts Person Address Account 1

21 public class Address { private String street; private int number; private String town; // constructor declaration public Address() { street = undeclared undeclared"; number = 0; town = undeclared undeclared"; Outline 21 public Address(String street, int number, String town) { this.street street = street; this.number = number; this.town town= town; public Address(Address ad){ this.setstreet setstreet(ad. (ad.getstreet getstreet()); this.setnumber setnumber(ad. (ad.getnumber getnumber()); this.settown settown(ad. (ad.gettown gettown()); public String getstreet(){ return street; public int getnumber(){ return number;

22 public String gettown(){ return town; Outline 22 public void setstreet(string String ul){ street = ul; public void setnumber(int c){ number = c; public void settown(string m){ town = m; public String tostring() { return String.format format(" ("Street Street: %s number: %4d town: %s",getstreet getstreet(), getnumber(), gettown()); public void print() { System.out out.println println( this.tostring tostring());

23 public class Account { private int number; private int balance; Outline 23 // Konstruktory tridy Account public Account(){ this(0, 0); public Account(int number, int balance) { this.number = number; this.balance = balance; public void deposit (int( amount) { balance = balance + amount; public int withdraw (int amount) { balance = balance - amount; return balance; public int getnumber(){ return number; public void setnumber(int c){ number = c;

24 public int getbalance(){ return balance; public String tostring() { return String.format format(" ("Account number: %d account balance: %d", getnumber(), getbalance()); public void print() { System.out out.println println(this this.tostring tostring()); Outline 24

25 public class Person { private String name; private int yearbirth; private Address address; //whole part composition private Account account; // aggregation // constructor declaration public Person() { name = "undeclared" undeclared"; yearbirth = 0; address = new Address(); public Person(String name, int yearbirth, Address address) { this.name name= name; this.yearbirth = yearbirth; this.address = new Address(address address); //copy constructor //this this.address = address; also available // access and modification methods public void setname(string name) { this.name = name; Outline 25 public String getname(){ return name; public void setyearbirth(int int yearbirth) { this.yearbirth = yearbirth; public int getyearbirth() { return yearbirth;

26 public String tostring() { String tx= String.format format(" ("\nname nname: %s year of birth: %4d\nAddress naddress: "+ "%s\naccount naccount: %s", getname etname(), getyearbirth(), address.tostring tostring(), account.tostring tostring()); return tx; public void print() { System.out out.println println(this this.tostring tostring()); //address address.print print(); account.print print(); already declared in tostring // method public void setaccount(account account) { this.account = account; Outline 26 public Account getaccount(){ return account; public void deposit(int int amount){ account.deposit(.deposit(amount amount); public void withdraw(int int amount) { account.withdraw withdraw(amount amount); public void accountprint(){ System.out out.println println(" ("Account Account: "+account account.tostring tostring()); public void addressprint(){ System.out out.println println(" ("Address Address: "+ address.tostring tostring());

27 public class PersonTest { public static void main(string String[] args) { Address a1 = new Address(" ("Green Green",237," ",237,"Havirov Havirov"); //Address a2 = new Address("30. april",22,"ostrava"); Person o1 = new Person("Kamil",1988,a1); Person o2 = new Person("Peter",1956, ("Peter",1956,new Address("30. ("30.april april", 22,"Ostrava")); Account u1 = new Account(1,200); o1.setaccount setaccount(u1); o2.setaccount setaccount(u1); o1.print print(); o2.print print(); o1.withdraw withdraw(300); o2.deposit(800); u1.print print(); //stale zustava odkaz u1 = null; o1.accountprint accountprint(); o2.addressprint addressprint(); Outline 27

28 Graphical representation of the links among objects 28 street value name yearbirth value value number town value value address account number value balance value person account

29 Example of composition of objects Employee and Date 29 Class Employee accepts already created objects of class Date in its constructor Date -day -month -year 2 1 Employee -firstname -secondname

30 public class Date { private int month; // private int day; // based on month private int year; // any year // constructor: call checkmonth to confirm proper value for month; // call checkday to confirm proper value for day public Date( int themonth, int theday, int theyear ) { month = checkmonth( themonth ); // validate month year = theyear; // could validate year day = checkday( theday ); // validate day System.out.printf( "Date object constructor for date %s\n", % this ); // end Date constructor // utility method to confirm proper month value private int checkmonth( int testmonth ) { if ( testmonth > 0 && testmonth <= 12 ) // validate month return testmonth; else // month is invalid { System.out.printf( "Invalid month (%d) set to 1.", testmonth ); return 1; // maintain object in consistent state // end else // end method checkmonth Outline 30

31 // utility method to confirm proper day value based on month and year private int checkday( int testday ) { int dayspermonth[] = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ; Outline 31 // check if day in range for month if ( testday > 0 && testday <= dayspermonth[ month ] ) return testday; // check for leap year if ( month == 2 && testday == 29 && ( year % 400 == 0 ( year % 4 == 0 && year % 100!= 0 ) ) ) return testday; System.out.printf( "Invalid day (%d) set to 1.", testday ); return 1; // maintain object in consistent state // end method checkday // return a String of the form month/day/year public String tostring() { return String.format( "%d/%d/%d d/%d/%d", month, day, year ); // end method tostring // end class Date

32 public class Employee { private String firstname; private String lastname; private Date birthdate; private Date hiredate; Outline 32 // constructor to initialize name, birth date and hire date public Employee( String first, String last, Date dateofbirth, Date dateofhire ) { firstname = first; lastname = last; birthdate = dateofbirth; hiredate = dateofhire; // end Employee constructor // convert Employee to String format public String tostring() { return String.format format( "%s, %s Hired: %s Birthday: %s", lastname, firstname, hiredate, birthdate ); // end method toemployeestring // end class Employee

33 public class EmployeeTest { public static void main( String args[] ) { Date birth = new Date( 7, 24, 1949 ); Date hire = new Date( 3, 12, 1988 ); Employee employee = new Employee( "Bob", "Blue", birth, hire ); Outline 33 System.out.println( employee ); Employee e1 = new Employee( John John, Frost Frost, new Date(12, 4, 1981), new Date(11, 18, 1950)); System.out.println(e1); // end main // end class EmployeeTest

34 Graphical representation of the links among objects 34 firstname lastname birthday hireday value value month value day value year value month value day value employee birth year value hire

35 Difference between empty String and a String referring to null 35 there are two different things: empty String is a valid String query by if (s == ) command in case a String refers nowhere it refers to null query by if (s == null) command

36 Use of Packages 36 packages (projects in BlueJ) are useful for gathering (aggregation) of the related classes packages helps to get rid of the name conflict by adding thae class name as a suffix to the name of package (package name.class name) e.g. full name of the class Date is: java.util.date e.g. java.awt (Abstract Window Toolkid) contains List class and java.util has an interface List example { java.awt.list list1; // List gui java.util.list list2; // abstract List namespace (introduced by Java and used by other systems too)

37 Packages - Creation 37 Class belonging into a given package must start with a command: package name_of_the_package; name_of_the_package must be the same as a name of directory, in which the file is placed (stored) name of parcels - convention: lower case characters, numbers and special character such as _ and $ package name is not allowed to be the same as Java key word, not start with a number character menu Edit \ New package during declaration packages can be nested (like windows directories)

38 Java API Packages Application Programming Interface 38 Java contains many predefined classes that are gathered into packages declaration import specifies that a program uses e.g. Scanner class from a package java.utils import java.util.scanner; overview of the predefined packages is given in the following tables

39 Java API packages 39 Package java.applet java.awt java.awt.event Description The Java Applet Package contains a class and several interfaces required to create Java applets program that execites in Web browsers. The Java Abstract Window Toolkid Package contains the classes and interfaces required to create and manipulate GUIs in Java 1.0 and 1.1 Current version of Java often uses javax.swing instead. The Java Abstract Window Toolkid Event Package contaions classes and interfaces that enable event handling for GUI components in both the java.awt and javax.swing packages.

40 Java API packages 40 Package Description java.io The Java Input Output Package contains classes and interfaces that enable programs to input and output data. java.lang java.net The Java Language Package contains classes and interfaces that are required by many Java programs. This package is imported implicitly. The Java Networking Package contains classes and interfaces that enable programs to communicate via computer networks like the Internet.

41 Java API packages 41 Package Description java.text java.util The Java Text Package contains classes and interfaces that enable programs to manipulate numbers, dates, characters and strings. The package provides internationalization capabilities that enable a program to be customized to a specific locate. The Java Utilities Package cintains utulity classes and interfaces that enable: manipulate time and date work with random numbers the storing and processing of large amount of data the breaking the strings into a smaller pieces called token

42 Java API packages 42 Package Description javax.swing javax.swing.event The Java Swing GUI Components Package contains classes and interfaces for Java s Swing GUI components that provide support for portable GUIs. The Java Swing Event Package contains classes and interfaces that enable event handling for GUI components in the javax.swing package

43 Packages User View 43 Java enables to gather group of classes into hierarchy arranged packages. Convention: source class files belonging to the common package are stored into the same directory Compiler arranges compiled files in the same way Source and compiled files need not be in the same directory (BlueJ places source files *.java as well as compiled files *.class into the same directory)

44 Packages Notation 44 Names of the hierarchy ordered packages are separated by a coma. e.g. import java.util.date import command that integrates the package into an application. The only command that can precede is the package command. java package with the name java util subpackage of the java package Date name of the imported class object declaration with the import command: Date dnes; // just qualification, without a constructor object declaration without the import command: java.util.date dnes;

45 JAR Java Archives Files 45 JAR file format enables you to bundle multiple files into a single archive file. Typically a JAR file contains the class files and auxiliary resources associated with applications.

46 JAR File Format Benefits 46 Security digital sign of the contents of a JAR file. Decreasing download time Compression JAR format allows to compress files Packaging for extension: The extension framework provides a means by which you can add functionality to Java core platform. Package sealing: JAR files can be optionally sealed so that the package can enforced version consistency.

47 Using JAR Files: The Basics 47 JAR files are packed with the ZIP file format. You can use them for ZIP-like tasks such as lossless data compression, decompression, archiving and archive unpacking.

48 Table of Basic Operation 48 Operation To create a JAR file To view the contents of a JAR file To extract the contents of a JAR file To extract specific files from a JAR file To run application packaged as a JAR file (require the Main-class manifest header) Command jar cf jar-file input-file(s) jar tf jar-file jar xf jar-file jar xf jar-file archives-file(s) java jar app.jar

49 Creating a JAR File Independent Application 49 a JAR file cam be executed like an independent application with use only JRE (15 MB) instead of JDK (50 MB). all files in the project are stored in the jar file there must be a main method

50 Creation a JAR File with Application 50 BlueJ: Project Create JAR File Select File with the main class before JAR file creation it is necessary to copy the whole application into an independent package (otherwise all files in the package will be ziped too)