Презентация 4. Java OOP. 5. Abstract Classes онлайн
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Слайды и текст к этой презентации:
№1 слайд
Содержание слайда: 4. Java OOP
5. Abstract Classes. Interfaces
№2 слайд
Содержание слайда: Abstract Classes
An abstract class is a class that is declared abstract
Abstract classes cannot be instantiated, but they can be subclassed
№3 слайд
Содержание слайда: Abstract Methods
An abstract method is a method that is declared without an implementation:
abstract void moveTo(double deltaX, double deltaY);
If a class includes abstract methods, the class itself must be declared abstract
№4 слайд
Содержание слайда: An Abstract Classes II
A subclass of an abstract class usually provides implementations for all of the abstract methods in its parent class
If it does not, the subclass must also be declared abstract
Abstract classes can contain fields and implemented methods (partial implementation)
An abstract class may have static fields and static methods. You can use these static members with a class reference as you would with any other class
№5 слайд
Содержание слайда: Example: Abstract DepoBase Class
Modify 442InterestSum project using DepoBase as an abstract class.
№6 слайд
Содержание слайда: Example: Abstract DepoBase Class
See 451AbstractDepo project for the full text
№7 слайд
Содержание слайда: How to Create and Use Library
To create depo library:
Right click on the app package -> Export -> Java -> JAR file -> Next
JAR file = depo.jar
Finish
How you can use depo.jar library:
Create new project 451aAbstractDepo
Right click on the project name -> Build Path
-> Configure Build Path
Go to Library tab -> Add External JARs -> find and click on depo.jar -> Open -> Ok
№8 слайд
Содержание слайда: Interfaces
An interface is a reference type, similar to a class, that can contain only constants, method signatures, and nested types
There are no method bodies
Interfaces cannot be instantiated—they can only be implemented by classes or extended by other interfaces
№9 слайд
Содержание слайда: Defining an Interface
An interface declaration consists of:
modifiers
the keyword interface
the interface name
a comma-separated list of parent interfaces (if any)
the interface body
An interface can extend any number of interfaces
№10 слайд
Содержание слайда: Interface Definition Example
public interface GroupedInterface extends
Interface1, Interface2, Interface3 {
// constant declarations
double E = 2.718282;
// method signatures
void doSomething (int i, double x);
int doSomethingElse(String s);
}
№11 слайд
Содержание слайда: The Interface Body
The interface body contains method declarations for all the methods included in the interface
A method declaration within an interface is followed by a semicolon, but no braces
All methods declared in an interface are implicitly public
An interface can contain constant declarations in addition to method declarations
All constant values defined in an interface are implicitly public, static, and final
№12 слайд
Содержание слайда: Use an Interface
To use an interface, you write a class that implements the interface
When an instantiable class implements an interface, it provides a method body for each of the methods declared in the interface
public class OperateBMW760i implements GroupedInterface {
. . . .
}
№13 слайд
Содержание слайда: Interfaces and Multiple Inheritance
In Java, a class can inherit from only one class but it can implement more than one interface
This means that if a variable is declared to be the type of an interface, its value can reference any object that is instantiated from any class that implements the interface
№14 слайд
Содержание слайда: Using an Interface as a Type
You can use interface names anywhere you can use any other data type name
If you define a reference variable whose type is an interface, any object you assign to it must be an instance of a class that implements the interface
№15 слайд
Содержание слайда: Exercise: InterestInterface
Modify 442InterestSum project using interface
№16 слайд
Содержание слайда: Exercise: InterestInterface
See 452InterfaceDepo project for the full text
№17 слайд
Содержание слайда: Cloning (1 of 2)
Use clone() method to get independent object instead of object’s assignment
clone() method can make only a field-by-
field copy
Cloning is correct if a class contains only primitive fields or references to immutable objects
“Deep” cloning is necessary otherwise
№18 слайд
Содержание слайда: Cloning (2 of 2)
The clone method is a protected method of Object, which means that your code cannot simply call it
To make clone method accessible a class must:
Implement the Cloneable interface
Redefine the clone method with the public access modifier.
№19 слайд
Содержание слайда: Deep Cloning
To make a deep copy, you have clone the mutable instance fields in the redefined clone method
№20 слайд
Содержание слайда: Example: DepoBase Cloning
public abstract class DepoBase implements Cloneable{
. . . . . .
public DepoBase clone() throws CloneNotSupportedException{
DepoBase cln = (DepoBase)super.clone();
cln.startDate = (Date)startDate.clone();
return cln;
}
. . . . . .
}
№21 слайд
Содержание слайда: Interfaces in Java SE 8
The interface body can contain:
abstract methods (followed by a semicolon, but no braces – it does not contain an implementation
default methods (are defined with the default modifier)
static methods (with the static keyword)
constant declarations
№22 слайд
Содержание слайда: Interface Default Methods
You specify that a method definition in an interface is a default method with the default keyword at the beginning of the method signature
Default method defines a default implementation
Default methods enable you to add new functionality to the interfaces of your libraries and ensure binary compatibility with code written for older versions of those interfaces
Any class that implements the interface with default method will have this method already defined
№23 слайд
Содержание слайда: Exercise: Default Method
Modify 452InterfaceDepo project:
Remove abstract DepoBase class
Add calculateInterest method as default method of the InterestInterface
№24 слайд
Содержание слайда: Exercise: Default Method
See 453DefaultMethod project for the full text
№25 слайд
Содержание слайда: Functional Interfaces
A functional interface is any interface that contains only one abstract method
A functional interface may contain one or more default methods or static methods
The abstract method of a functional interface can be implemented with help of lambda expression
№26 слайд
Содержание слайда: Lambda Expression
A lambda expression looks a lot like a method declaration
You can consider lambda expressions as anonymous methods—methods without a name
№27 слайд
Содержание слайда: Example of Lambda Expression I
public class Calculator {
interface IntegerMath {
int operation(int a, int b);
}
public int operateBinary(int a, int b, IntegerMath op) {
return op.operation(a, b);
}
№28 слайд
Содержание слайда: Example of Lambda Expression II
public static void main(String... args) {
Calculator myApp = new Calculator();
IntegerMath addition = (a, b) -> a + b;
IntegerMath subtraction = (a, b) -> a - b;
System.out.println("40 + 2 = " +
myApp.operateBinary(40, 2, addition));
System.out.println("20 - 10 = " +
myApp.operateBinary(20, 10, subtraction));
}
}
№29 слайд
Содержание слайда: Example of Lambda Expression
See 454LambdaCalulator for the full text
№30 слайд
Содержание слайда: Lambda Expression Syntax I
A lambda expression consists of the following:
a comma-separated list of formal parameters enclosed in parentheses
the arrow token, ->
a body, which consists of a single expression or a statement block
№31 слайд
Содержание слайда: Lambda Expression Syntax II
You can omit the data type of the parameters in a lambda expression
You can omit the parentheses if there is only one parameter
If you specify a single expression, then the Java runtime evaluates the expression and then returns its value
Alternatively, you must enclose statements in braces {}
№32 слайд
Содержание слайда: Manuals
http://docs.oracle.com/javase/tutorial/java/IandI/index.html
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