Dr. Andrew Wallace PhD . BEng. (hons) . EurIng. andrew@cs.umu.se. O. verview. Abstraction. Polymorphism. Interface. Package. Shadows . Object Serialization. Quiz. What is inheritance in Java?. How do you organise code between classes and their sub classes?. ID: 411644
DownloadNote - The PPT/PDF document "More on Inheritance" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Presentations text content in More on Inheritance
Slide1
More on Inheritance
Dr. Andrew Wallace PhD
BEng
(hons)
EurIng
andrew@cs.umu.se
Slide2
Overview
Abstraction
Polymorphism
Interface
Package
Shadows
Object Serialization
Slide3
Quiz
What is inheritance in Java?
How do you organise code between classes and their sub classes?
Slide4
Abstraction
Some times it is advantageous to partly implement a superclass
Functionality that changes among sub classes
Abstraction is when a class is partly defined
Interface and abstraction
Interface – 100% abstraction
Abstraction - <= 100% abstraction
You can’t instantiate an abstract class
Slide5
Abstraction
abstract class
MyClass
{
public abstract void
myMethod
(
int
in);
public abstract
int
myOtherMethod
();
public void float
yetAnotherMethod
(){return 1.0;}
}
Slide6
Abstraction
class
MySubClass
extends
MyClass
{
public void
myMethod
(
int
in)
{
…
}
public
int
myOtherMethod
()
{
…
}
}
Slide7
Quiz
What is an abstract class?
How does an abstract class differ from an interface?
What is the difference between overloaded and overridden methods?
Slide8
Polymorphism
Take on many differ formsUsing parent class to refer to a child… is a … All cats are mammals therefore …All mammals are cats?
Slide9
Polymorphism
class Animalclass Dinosaur extends Animalclass Stegosaurus extends Dinosaur
Animal
Dinosaur
Stegosaurus
Slide10
Polymorphism
Dinosaur d = new Stegosaurus();Stegosaurus s = new Dinosaur();
Slide11
Polymorphism
Object type dictates the methods available
Not it’s reference
Dinosaur d = new Stegosaurus();
d can access all Animal methods and Stegosaurus methods
But what about overridden methods?
Slide12
Polymorphism
public class Dinosaur { public void walk(){System.out.println(“Dinosaur walking”);}} public class Stegosaurus extends Dinosaur { public void walk(){System.out.println(“Stegosaurus walking”);}}Dinosaur d = new Stegosaurus();d.walk();Stegosaurus walking
Dynamic binding
Slide13
Polymorphism
public class Dinosaur { public void walk(){System.out.println(“Dinosaur walking”);}} public class Stegosaurus extends Dinosaur { public void walk(){System.out.println(“Stegosaurus walking”);} public void eatGrass(){ … };}Dinosaur d = new Stegosaurus();d.eatGrass();
Slide14
Quiz
How is polymorphism implemented in Java?
Why can a superclass reference not call a method defined in a subclass?
Slide15
Interface
Polymorphism works for interfaces as for abstract
Classes can implement multiple interfaces
class
MyClass
implements Interface1, Interface2, Interface3
Interfaces can extend other interfaces
i
nterface Interface2 extends Interface1
Interfaces cannot implement other Interfaces
As they don’t implement any code!
Slide16
Package
Collection of classes
The classes in a packet can have a related function and depend on each other (same project or sub project)
No need for inheritance within the packet
Java has many packets
Util
Awt
Swing
Io
Lang
Slide17
Package
Create your own package
Naming convention
Hierarchical
Domain name of organisation that created it then organisation name
Subpackets
separated by dots
se.umu.ce.mypacket.mysubpacket
Package keyword
Start of file
p
ackage
se.umu.ce.mypacket.mysubpacket
;
Slide18
Package
To use a package
i
mport
packagename.classname
;
import
packagename
.*;
import
se.umu.ce.mypacket.mysubpacket
.*;
Packages map to directory structure
Classpath
Eleclips
– new package
Slide19
Shadows
Variables or classes in differ blocks but with the same name
Public class
MyClass
{
int
x;
public void
MyMethod
()
{
x = 1;
int
x = 5;
System.out.println
(x);
}
}
Slide20
Shadows
p
ackage
M
yPackage
;
p
ublic class
MyClass
{ … }
p
ackage
MyOtherPackage
;
Import
M
yPackage
;
p
ublic class
MyClass
{
public void
MyMethod
()
{
MyClass
m = new
MyClass
();
MyPackage.MyClass
pm = new
MyPackage.MyClass
();
}
}
Slide21
Object Serialization
Preserve the state of an object between runsSave an object to a file and the recreate it in the same stateTransmit the object form one machine to another
Slide22
Object Serialization
Implement the
Serializable
interface (in java.io)
All class members must be serializable else marked
Download this presentation
DownloadNote - The PPT/PDF document "More on Inheritance" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Presentations text content in More on Inheritance
More on Inheritance
Dr. Andrew Wallace PhD
BEng
(hons)
EurIng
andrew@cs.umu.se
Slide2Overview
Abstraction
Polymorphism
Interface
Package
Shadows
Object Serialization
Slide3Quiz
What is inheritance in Java?
How do you organise code between classes and their sub classes?
Slide4Abstraction
Some times it is advantageous to partly implement a superclass
Functionality that changes among sub classes
Abstraction is when a class is partly defined
Interface and abstraction
Interface – 100% abstraction
Abstraction - <= 100% abstraction
You can’t instantiate an abstract class
Slide5Abstraction
abstract class
MyClass
{
public abstract void
myMethod
(
int
in);
public abstract
int
myOtherMethod
();
public void float
yetAnotherMethod
(){return 1.0;}
}
Slide6Abstraction
class
MySubClass
extends
MyClass
{
public void
myMethod
(
int
in)
{
…
}
public
int
myOtherMethod
()
{
…
}
}
Slide7Quiz
What is an abstract class?
How does an abstract class differ from an interface?
What is the difference between overloaded and overridden methods?
Slide8Polymorphism
Take on many differ formsUsing parent class to refer to a child… is a … All cats are mammals therefore …All mammals are cats?
Slide9Polymorphism
class Animalclass Dinosaur extends Animalclass Stegosaurus extends Dinosaur
Animal
Dinosaur
Stegosaurus
Slide10Polymorphism
Dinosaur d = new Stegosaurus();Stegosaurus s = new Dinosaur();
Slide11Polymorphism
Object type dictates the methods available
Not it’s reference
Dinosaur d = new Stegosaurus();
d can access all Animal methods and Stegosaurus methods
But what about overridden methods?
Slide12Polymorphism
public class Dinosaur { public void walk(){System.out.println(“Dinosaur walking”);}} public class Stegosaurus extends Dinosaur { public void walk(){System.out.println(“Stegosaurus walking”);}}Dinosaur d = new Stegosaurus();d.walk();Stegosaurus walking
Dynamic binding
Slide13Polymorphism
public class Dinosaur { public void walk(){System.out.println(“Dinosaur walking”);}} public class Stegosaurus extends Dinosaur { public void walk(){System.out.println(“Stegosaurus walking”);} public void eatGrass(){ … };}Dinosaur d = new Stegosaurus();d.eatGrass();
Slide14Quiz
How is polymorphism implemented in Java?
Why can a superclass reference not call a method defined in a subclass?
Slide15Interface
Polymorphism works for interfaces as for abstract
Classes can implement multiple interfaces
class
MyClass
implements Interface1, Interface2, Interface3
Interfaces can extend other interfaces
i
nterface Interface2 extends Interface1
Interfaces cannot implement other Interfaces
As they don’t implement any code!
Slide16Package
Collection of classes
The classes in a packet can have a related function and depend on each other (same project or sub project)
No need for inheritance within the packet
Java has many packets
Util
Awt
Swing
Io
Lang
Slide17Package
Create your own package
Naming convention
Hierarchical
Domain name of organisation that created it then organisation name
Subpackets
separated by dots
se.umu.ce.mypacket.mysubpacket
Package keyword
Start of file
p
ackage
se.umu.ce.mypacket.mysubpacket
;
Slide18Package
To use a package
i
mport
packagename.classname
;
import
packagename
.*;
import
se.umu.ce.mypacket.mysubpacket
.*;
Packages map to directory structure
Classpath
Eleclips
– new package
Slide19Shadows
Variables or classes in differ blocks but with the same name
Public class
MyClass
{
int
x;
public void
MyMethod
()
{
x = 1;
int
x = 5;
System.out.println
(x);
}
}
Slide20Shadows
p
ackage
M
yPackage
;
p
ublic class
MyClass
{ … }
p
ackage
MyOtherPackage
;
Import
M
yPackage
;
p
ublic class
MyClass
{
public void
MyMethod
()
{
MyClass
m = new
MyClass
();
MyPackage.MyClass
pm = new
MyPackage.MyClass
();
}
}
Slide21Object Serialization
Preserve the state of an object between runsSave an object to a file and the recreate it in the same stateTransmit the object form one machine to another
Slide22Object Serialization
Implement the
Serializable
interface (in java.io)
All class members must be serializable else marked
transient
transient private String
strString
;
Transient are derived at run time
Use the
ObjectOutputStream
to write the object to a file
writeObject
Use the
ObjectInputStream
to
deserialize
the object
r
eadObject
Slide23Object Serialization
c
lass
MyClass
implements
Serializable
{}
MyClass
m = new
MyClass
();
t
ry
{
FileOutputStream
f = new
FileOutputStream
(“
file.ser
”);
ObjectOutputStream
out = new
OutputObjectStrea
(f);
out.writeObject
(m);
Out.close
();
f.close
();
}
Slide24Quiz
What is a package in Java?
How can you save the state of a object in Java?
Slide25Questions?
Slide26Slide27Slide28Slide29Slide30