Application
Programming
Hend Alkittawi

OOP Concepts
Introduction to Java Interfaces

INTERFACES
-

Java interfaces are particularly useful for assigning common
functionality to possibly unrelated classes

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Java interfaces offer a capability requiring that unrelated classes
implement a set of common methods

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A Java interface describes a set of methods that can be called on an
object to tell it to perform some tasks or return some piece of
information

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An interface should be used in place of an abstract class when there is
no default implementation to inherit, that is, no fields and no
concrete methods implementations
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this allows objects of unrelated classes to be processed polymorphically

INTERFACES
-

An interface declaration begins with the keywords interface
and contains only constants and abstract methods
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all methods declared in an interface are implicitly public
abstract methods

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all fields are implicitly public, static, and final
public interface InterfaceName {
public static final dataType varName;
public abstract returnType interfaceMethod();
}

INTERFACES
-

To use an interface, a concrete class must specify that it
implements the interface and must declare each method in the
interface with the signature specified in the interface
declaration

-

Java does not allow subclasses to inherit from more than one
superclass, but it allows a class to inherit from one
superclass and implement as many interfaces as it needs
public class ClassName implements InterfaceName
or
public class ClassName extends SuperClass implements InterfaceName
where InterfaceName maybe a comma-separated list of interface names

public interface Drawable {
public void draw();
}

public class InterfaceDemo {
public static void main(String[] args) {
// Creating objects of different
// classes that implement Drawable
Drawable rectangle = new Rectangle(2.5, 7.2);
Drawable tree = new Tree("Oak", 5.5);
Drawable person = new Person("John", 30);

public class Tree implements Drawable {
private String type;
private double height;
public Tree(String type, double height) {
this.type = type;
this.height = height; }

// Array of Drawable objects
Drawable[] drawables = {rectangle, tree, person};

// getters and setters are omitted

// Drawing all drawable objects
for (Drawable drawable : drawables) {
drawable.draw();
}

@Override
public void draw() {
System.out.println("Drawing a tree with height " + getHeight() + " meters"); }
}

}
}

public class Rectangle implements Drawable{
private double length;
private double width;
public Rectangle(double length, double width) {
this.length = length;
this.width = width; }
// getters and setters are omitted
public void draw() {
System.out.println("Drawing a rectangle with length " + length + " and width " + width); }
}

CODE DEMO
-

Create classes to demo
interfaces concepts!

DO YOU HAVE ANY
QUESTIONS?

THANK
YOU!

@

hend.alkittawi@utsa.edu

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