Java 8 Default Methods

Java 8 Default Methods
Haim Michael
September 19th
, 2017
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Haim Michael Introduction
● Snowboarding. Learning. Coding. Teaching. More
than 18 years of Practical Experience.
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Haim Michael Introduction
● Professional Certifications
Zend Certified Engineer in PHP
Certified Java Professional
Certified Java EE Web Component Developer
OMG Certified UML Professional
● MBA (cum laude) from Tel-Aviv University
Information Systems Management
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Introduction
 The interfaces we define are kind of contracts
that specify which methods should be defined
in each and every class that implements them.
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interface IBrowser
{
public void browse(URL address);
public void back();
public void forward();
public void refresh();
}
IBrowser browser = new Firefox();

Introduction
 The interface in Java is a reference type,
similarly to class.
 The interface can include in its definition only
public final static variables (constants), public
abstract methods (signatures), public default
methods, public static methods, nested types
and private methods.
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Introduction
 The default methods are defined with the
default modifier, and static methods with the
static keyword. All abstract, default, and static
methods in interfaces are implicitly public. We
can omit the public modifier.
 The constant values defined in an interface are
implicitly public, static, and final. We can omit
these modifiers.
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Public Final Static Variables
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 Although Java allows us to define enums,
many developers prefer to use interfaces that
include the definition of public static variables.
public interface IRobot {
public final static int MAX_SPEED = 100;
public final static int MIN_SPEED = 10;

Public Abstract Methods
 The public abstract methods we define are
actually the interface through which objects
interact with each other.
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public abstract void moveRight(int steps);
public abstract void moveLeft(int steps);
public abstract void moveUp(int steps);
public abstract void moveDown(int steps);
}

Default Methods
 As of Java 8 the interface we define can
include the definition of methods together with
their implementation.
 This implementation is known as a default one
that will take place when the class that
implements the interface doesn't include its
own specific implementation.
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Default Methods
lifemichael
public default void turnAround() {
moveRight(1);
moveRight(1);
moveRight(1);
moveRight(1);
}
}

Default Methods
 When extending an interface that contains a
default method, we can let the extended
interface inherit the default method, we can
redeclare the default method as an abstract
method and we can even redefine it with a
new implementation.
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Static Methods
 The interface we define can include the
definition of static methods.
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Static Methods
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public static String getIRobotSpecificationDetails() {
return "spec...";
}
moveRight(1);
moveRight(1);
moveRight(1);
moveRight(1);
}
}

Nested Types
 The interface we define can include the
definition of new static inner types.
 The inner types we define will be implicitly
static ones.
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Nested Types
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public static String getIRobotSpecificationDetails() {
return "spec...";
}
moveRight(1);
moveRight(1);
moveRight(1);
moveRight(1);
}
public static class Engine {
public void doSomething() {
getIRobotSpecificationDetails();
}
}
}

Nested Types
 We can find an interesting example for
defining abstract inner type inside an interface
when developing a remote service on the
android platform.
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Nested Types
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public interface ICurrencyService extends android.os.IInterface
{
public static abstract class Stub extends android.os.Binder
implements ICurrencyService
{
}
public double getCurrency(java.lang.String currencyName)
throws android.os.RemoteException;
}

Private Methods
 As of Java 9, the interface we define can
include the definition of private methods.
 Highly useful when having more than one
default methods that share parts of their
implementations. We can place the common
parts in separated private methods and make
our code shorter.
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Private Methods
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package com.lifemichael;
...
moveRight(1);
step();
moveRight(1);
step();
...
}
private void step(){
//...
}
}

Interfaces as APIs
 Companies and organizations that develop
software to be used by other developers use
the interface as API.
 While the interface is made public, its
implementation is kept as a closely guarded
secret and it can be revises at a later date as
long as it continues to implement the original
interface.
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Interfaces as Types
 The new defined interface is actually a new
type we can use whenever we define a
variable or a function parameter.
 Using the interface name as a type adds more
flexibility to our code.
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Evolving Interfaces
 When we want to add more abstract methods
to an interface that was already defined, all
classes that implement the old interface will
break because they no longer implement the
old interface. Developers relying on our
interface will protest.
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Evolving Interfaces
 We can either define a new interface that
extend the one we already have, or define the
new methods as default ones.
 The default methods allow us to add new
functionality to interfaces we already defined,
while keeping the binary compatibility with
code written for older versions of those
interfaces.
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Interface as a Dictating Tool
 We can use interfaces for dictating specific
requirements from other developers for using
functions we developed.
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Interfaces as Traits
 Using the default methods we can develop
interfaces that will be used as traits in order to
reduce the amount of code in our project.
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Questions & Answers
If you enjoyed my lecture please leave me a comment
at http://speakerpedia.com/speakers/life-michael.
Thanks for your time!
Haim.

Java 8 Default Methods

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