package - cs.upt.rocs.upt.ro/~cristina/teaching/oop-en/packages.pdf · java -cp paths_to_bin...

Dr. Petru Florin Mihancea

Packages

package

A

B

<<interface>>X

YZ

C

C1 C2

ro.upt.oop.name3

ro.upt.oop.name1ro.upt.oop.name2

support for organizing a

system into subsystems

(modules)


APackages: Basic Elements


packagepackage ro.upt.oop.curs.ceasuri;public interface ClockType {! public void setTime(int h, int n, int s);! public String toString();!}abstract class AbstractClock implements ClockType {

! private int hour, minute, second;

! public AbstractClock() {! ! hour = minute = second = 0;! }! public void setTime(int h, int m, int s) {! ! hour = (h >= 0) && (h < 24) ? h : 0;! ! minute = (m >= 0) && ( m < 60) ? m : 0;! ! second = (s >= 0) && ( s < 60) ? s : 0;! }! public String toString() {! ! return "Current time " + hour + ":" + ! ! ! ! minute + ":" + second; ! }}

package ro.upt.oop.curs.ceasuri;public class Clock extends AbstractClock {!! public String toString() {! ! return "Normal clock - " + super.toString();! }}

package ro.upt.oop.curs;...public class Ceasornicar {! public void regleaza(ClockType x) {! ! x.setTime(12, 0, 0);! }}

compilation units(files); all the contained

classes/interfaces belong to the mentioned package

package name(identif1.identif2. ... identifN)

package is written on the first

non-commented line from a

compilation unit; if it is missing,

the content of the file belongs to

the anonymous package/without

name/default


complete qualified name

package ro.upt.oop.curs.ceasuri;public interface ClockType {! public void setTime(int h, int n, int s);! public String toString();!}abstract class AbstractClock implements ClockType {



package ro.upt.oop.curs;public class Ceasornicar {! public void regleaza(ClockType x) {! ! x.setTime(12, 0, 0);! }}

A package represents also a distinct space name for classes/interfaces; for example,

we might have classes with the same simple name in different packages

packageName.className

package ro.upt.oop.curs;public class Ceasornicar { public void regleaza(ro.upt.oop.curs.ceasuri.ClockType x) {! x.setTime(12, 0, 0); }}

In the same package we do NOT have

ClockType?!?!

Ceasornicar.java:4

: error: cannot find sym

bol

!public vo

id regleaza(ClockType x) {

!

^

symbol: cl

ass ClockType

location: clas

s Ceasornicar

1 error


Quizzpackage ro.upt.oop.curs.ceasuri;public class Clock extends AbstractClock {!! public String toString() {! ! return "Normal clock - " + super.toString();! }}

In the same package we do NOT have

ClockType ?!?!

Ceasornicar.java:1

1: error: cannot find sym

bol

!public C

lock create() {

!

^

symbol: cl

ass Clock

location: clas

s Test

Ceasornicar.java:1

2: error: cannot find sym

bol

!!

return new Clock();

!!

^

symbol: cl

ass Clock

location: clas

s Test

2 errors

package ro.upt.oop.curs;class Test {! public ro.upt.oop.curs.ceasuri.Clock create() {! ! return new ro.upt.oop.curs.ceasuri.Clock();! }}

package ro.upt.oop.curs;class Test {! public Clock create() {! ! return new Clock();! }}

We have to use the full qualified name

when we declare a reference, create an

object,...


The alternativepackage ro.upt.oop.curs.ceasuri;public interface ClockType {! public void setTime(int h, int n, int s);! public String toString();!}abstract class AbstractClock implements ClockType {! private int hour, minute, second;! public AbstractClock() {! ! hour = minute = second = 0;! }! public void setTime(int h, int m, int s) {! ! hour = (h >= 0) && (h < 24) ? h : 0;! ! minute = (m >= 0) && ( m < 60) ? m : 0;! ! second = (s >= 0) && ( s < 60) ? s : 0;! }! public String toString() {! ! return "Current time " + hour + ":" + ! ! ! ! minute + ":" + second; ! }}

package ro.upt.oop.curs;import ro.upt.oop.curs.ceasuri.ClockType; public class Ceasornicar {! public void regleaza(ClockType x) {! ! x.setTime(12, 0, 0);! }}

At the beginning of the compilation unit (after package, if it exista)

import packageName.className;import packageName.*;

In the current compilation unit:Version 1 - we can use only the

mentioned class by its short nameVersion 2 -we can use all the classes

defined in the imported package


Attentionimport ro.upt.oop.curs.ceasuri.*;import tmp.*;...

Clock c; //Ambiguity error

We have another package tmp that contains a class Clock

We need to use the full name of the class or to import the class

1

2Import is exclusively used by the compiler for solving the name of the classes. There is no connection with the #include from C.

3Without a connection with #include, packages...(from java 1.5) existsimport static packageName.className.*;orimport static packageName.className.staticMemberName;for allowing the use (in the file where import static exists) the involved static members without specifying the class they belong to


Quizz

public class Automat {

! public static void main(String[] args) {! !! }

}

Class String belongs to java.lang and we are allowed to use it without using its complete qualified name or import.

Why the code is compiled?

java.lang is always considered

imported:)


UML

+regleaza(x : ClockType):void

Ceasornicar

+setTime(h:int,m:int,s:int):void+toString():String

<<interface>>ClockType

Dependency appears also at the classes level

Ceasornicar-ul DOES NOT have ClockType-uri (IS NOT a composition), IS NOT a clock (IS NOT an inheritance relation),but uses references/ methods from ClockType and depends on ClockType

ro.upt.oop.curs.ceasuriro.upt.oop.curs

pachetul

dependențaUn pahet (ro.upt.oop.curs) folosește elemente dintr-un alt pachet (ro.upt.oop.curs.ceasuri)


BAccess specifiers for

packages content


Visibility of packages content

publicthe class/interface can be used outside the package it belongs toAttentionthe class should belong to a file (compilation unit) with the same name as the class (followed bt .java); otherwise is a compilation error

default (without no specifier - a keyword does not exist) package access

the class/interface can be used only inside the package it belongs to

the class/interface belongs to

the “interface” of the package

the class/interface is an

implemantation detail of the

package


Examplespackage pachetA;

public class A { ...}

interface B {! public void aMethod();} package pachetB;

public class Client implements pachetA.B {//Error!! public void doSomething() {! ! pachetA.B x; //Error! ! pachetA.A a;! }

}

The file should be named A.java

package pachetA;

class Whatever implements B {!! public void aMethod() {! ! A a;! ! B b;

...! }}


CAccess specifiers

for member of classes in packages

the class that contain the

members is visible outside the

package


Access specifiers

privatethe member of the class (field/method) can be used only inside the class it belongs to

publicthe member of the class (field/method) can be used anywhere

protectedthe member of the class (field/method) can be used inside the class, inside its subclasses or inside the same package

Visibility in UML- private+ public# protected~ package access

default (without no specifier - a keyword does not exist) package access

the member of the class (field/method) can be used only inside the package it belongs to


Examplespackage pachet1;

public class A1 { private int x; public int y; protected int z; int t;}

package pachet1;

class B1 {! public void metodaB1() { A1 ob = new A1(); ob.x = 1; //Error ob.y = 1; //OK ob.z = 1; //OK ob.t = 1; //OK! } }

package pachet2;class A2 { public void metodaA2() { pachet1.A1 ob = new pachet1.A1(); ob.x = 1; //Error ob.y = 1; //OK ob.z = 1; //Error ob.t = 1; //Error } }class B2 extends pachet1.A1 { public B2() { x = 1; //Error y = 1; //OK z = 1; //OK t = 1; //Error } public void metodaB2() { pachet1.A1 ob = new pachet1.A1(); ob.x = 1; //Error ob.y = 1; //OK ob.z = 1; //Error (An error!) ob.t = 1; //Error } }


DOrganizing code

(source / machine)


We have this example...

package ro.upt.oop.curs.ceasuri;public interface ClockType {! public void setTime(int h, int n, int s);! public String toString();!}abstract class AbstractClock implements ClockType {



package ro.upt.oop.curs.ceasuri;public class Clock extends AbstractClock {!! public String toString() {! ! return "Normal clock - " + super.toString();! }}

package ro.upt.oop.curs;import ro.upt.oop.curs.ceasuri.*;public class Ceasornicar {! public void regleaza(ClockType x) {! ! x.setTime(12, 0, 0);! }! public static void main(String argv[]) {! ! Clock c = new Clock();! ! Ceasornicar om = new Ceasornicar();! ! om.regleaza(c);! ! System.out.println(c);! }}


Compiling & Running (I)

javac *.java

java

Exception in thread "main" java.lang.NoClassDefFoundError: Ceasornicar (wrong name: ro/upt/oop/curs/Ceasornicar)! at java.lang.ClassLoader.defineClass1(Native Method)! at java.lang.ClassLoader.defineClass(ClassLoader.java:792)! at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)! at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)! at java.net.URLClassLoader.access$100(URLClassLoader.java:71)! at java.net.URLClassLoader$1.run(URLClassLoader.java:361)! at java.net.URLClassLoader$1.run(URLClassLoader.java:355)! at java.security.AccessController.doPrivileged(Native Method)! at java.net.URLClassLoader.findClass(URLClassLoader.java:354)! at java.lang.ClassLoader.loadClass(ClassLoader.java:424)! at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)! at java.lang.ClassLoader.loadClass(ClassLoader.java:357)! at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:482)Pepis-MacBook-Pro:src Pepi$

Ceasornicarro.upt.oop.curs.Ceasornicar

Error: Could not find or load main class ro.upt.oop.curs.Ceasornicar


class files on the diskWe have into a compilaiton unit:

package name1.name2.name3;class X {...}public class Y {...}

On the disk we need to have:

A bin folder (or simillar)• name1 (folder)

• name2 (subfolder name1)• name3 (subfolder name2)

• X.class• Y.class

The compiler automatically distribute the files

javac -d path_to_bin *.java


ClasspathA frequent argument specific to the compiler, as well as to the virtual machine (-cp)

a path to the folders we distributed the .class files

the elements from the list are separated with : in unix systems and ; in windows systemsex. path1:path2:path3:...:pathN

from this folder the searching of the bytecode of a class will be performed when necessarily; it is based on the complete qualified name of the sub-folders as well as the .class the list may contains also java archives (jar files)

java -cp paths_to_bin ro.upt.oop.curs.Ceasornicar


Compiling (II)

Similar to the distribution of .class files, the sources(.java files) are distributed on folders/sub-folders according to the package name they

belong to


Compiling (II)We compile every package taking intoaccount the existing dependencies

ro.upt.oop.curs.ceasuriro.upt.oop.curs

1. javac -d path_to_bin path_to_package1_sources/*.java

2. javac -d path_to_bin -cp path_to_bin_already_compiled path_to_package_surces/*.java

2. javac -d path_to_bin path_to_package2_sources/*.java.javasrc/r

o/upt/oop/curs/Ceasornicar.j

ava:2: error: package

ro.upt.oop.curs.ceasuri does not exist

import ro.upt.oop.curs.ce

asuri.*;

^src/r

o/upt/oop/curs/Ceasornicar.j

ava:4: error: ca

nnot find

symbol

!public vo

id regleaza(ClockType x) {

!

^

symbol: cl

ass ClockType

location: clas

s Ceasornicar

cycling dependencies are a signal to a bad organization of a system.


Sourcepath

An argument specific to the compiler

a list of folder paths where we distributed source files (.java)

when we compile a compilation unit that depends on classes that have been not compiled, a search in these folders is performed in order to find the source files of these classes (following the subfolders of the classes)

package - cs.upt.rocs.upt.ro/~cristina/teaching/oop-en/packages.pdf · java -cp paths_to_bin...

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