Programming in Java - 10 -Packages

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Programming in JavaPackages


Packages

In Java, packages are a collection of classes Sort of like a namespace

Behaves the same way

Classes are declared as part of a package Packages can be broken part by sub packaging Many Java developers believe that all your code

should belong to a package


How to make a package?

Think of this as a namespace Insert a package statement at the top of the code

file(s) Any code file that is using the entities within a

package must either import the package, or reference the class through the package


Recall the Person and Employee classes

// Person.javaimport java.util.Date;class Person{

/* Protected Fields */protected String _firstName = "";protected String _lastName = "";/* Private Fields */protected Date _birthDate = new Date();/* Public Fields */public static int _population = 0;/* Constructors */public Person() { _population++; }public Person(String lastName, String firstName){

_lastName = lastName;_firstName = firstName;_population++;

}/* Private Methods */public static int getPopulation() { return _population; }/* Public Methods -- Getters */public String getFirstName() { return _firstName; }public String getLastName() { return _lastName; }public Date getBirthDate() { return _birthDate; }/* Public Methods -- Setters */public void setFirstName(String firstName){ _firstName = firstName ; }public void setLastName(String lastName) { _lastName = lastName; }

}

// Employee.javaimport java.util.Date;class Employee extends Person{

private String _jobTitle = "";private String _jobTitlePrefix = "";private String _department = "";private double _salary = 0.0;private Date _hireDate = null;private Date _terminationDate = null;

public Employee(Person p){

this.setFirstName(p.getFirstName());this.setLastName(p.getLastName());this._birthDate = p._birthDate;

}

public void setJobTitle(String jobTitle){ _jobTitle = jobTitle; }public void setJobTitlePrefix(String jobTitlePrefix){ _jobTitlePrefix = jobTitlePrefix; }public void setDepartment(String department){ _department = department; }public void setSalary(double salary){ _salary = salary; }public void setHireDate(Date hireDate){ _hireDate = hireDate; }public void setTerminationDate(Date terminationDate){ _terminationDate = terminationDate; }

public String getJobTitle() { return _jobTitle; }public String getJobTitlePrefix() { return _jobTitlePrefix; }public String getDepartment() { return _department; }public double getSalary() { return _salary; }public Date getHireDate() { return _hireDate; }public Date getTerminationDate() { return _terminationDate; }

}



// Person.javaimport java.util.Date;public class Person{




}

// Employee.javaimport java.util.Date;public class Employee extends Person{




}



}



// Person.javapackage person;import java.util.Date;public class Person{




}

// Employee.javapackage person;import java.util.Date;public class Employee extends Person{




}



}


Driver Code

// MainClass.javaimport person.*;class MainClass{

public static void main(String[] args){Employee em = new Employee(new Person(".Net", "WiBit"));System.out.println(em.getFirstName() + em.getLastName());

}

}


Class Path

Java uses an environment variable called CLASSPATH to seek java classes

Classes in a package should be contained within the same directory

This directory should be in a directory path dedicated for classes


Create Package

Create root class directory C:\WiBit.Net\Java\Classes

If not already, add this root class directory to the CLASSPATH environment variable (; delimited)

Create directory for person package C:\WiBit.Net\Java\Classes\person

Put Person.java and Employee.java in the person package directory


Create Package - Create root class directory

>_C:\

WiBit.Net

Java

Classes

Person.java

Employee.java

Src

MainClass.java

person


Create Package - Set Class Path (Not Set)

>echo %CLASSPATH%%CLASSPATH%

>_

C:\

WiBit.Net

Java

Classes

Person.java

Employee.java

Src

MainClass.java

person


Create Package - Set Class Path (Not Set)

>echo %CLASSPATH%%CLASSPATH%

>set CLASSPATH=.;C:\WiBit.Net\Java\Classes

>echo %CLASSPATH%.;C:\WiBit.Net\Java\Classes

>_

C:\

WiBit.Net

Java

Classes

Person.java

Employee.java

Src

MainClass.java

person


Create Package - Compile Person Package

C:\WiBit.Net\Java\Src>_C:\

WiBit.Net

Java

Classes

Person.java

Employee.java

Src

MainClass.java

person



C:\WiBit.Net\Java\Src>dir *.javaVolume in drive C has no label.Volume Serial Number is FA71-1060

Directory of C:\WiBit.Net\Java\Src

04/30/2011 03:38 PM 211 MainClass.java1 File(s) 211 bytes0 Dir(s) 146,006,347,776 bytes free

C:\WiBit.Net\Java\Src>_

C:\

WiBit.Net

Java

Classes

Person.java

Employee.java

Src

MainClass.java

person






C:\WiBit.Net\Java\Src>javac MainClass.java


C:\

WiBit.Net

Java

Classes

Person.java

Employee.java

Src

MainClass.java

person






C:\WiBit.Net\Java\Src>javac MainClass.java

C:\WiBit.Net\Java\Src>java MainClassWiBit.Net


C:\

WiBit.Net

Java

Classes

Person.java

Employee.java

Src

MainClass.java

person


Access the Packaged Classes

class MainClass

{

public static void main(String[] args)

{

person.Employee em =

new person.Employee(new person.Person(".Net", "WiBit"));

System.out.println(em.getFirstName() +

em.getLastName());

}

}


Access the Packaged Classes

import person.Employee;

import person.Person;

class MainClass

{

public static void main(String[] args)

{

Employee em = new Employee(new Person(".Net", "WiBit"));

System.out.println(em.getFirstName() +

em.getLastName());

}

}


The End?Thank You For Watching!

Programming in Java - 10 -Packages

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