Interface (Java): Difference between revisions

Revision as of 22:09, 5 October 2019

Revision as of 12:02, 16 December 2019

Line 11:

For example:

<source lang="Java">

interface Bounceable {

double pi = 3.1415;

void setBounce(); // Note the semicolon

// Interface methods are public, abstract and never final.

// Think of them as prototypes only; no implementations are allowed.

}

</source>

An interface:

* declares only method headers and public constants.

* cannot be instantiated.

* can be implemented by a class.

* cannot extend a class.

* can extend several other interfaces.

==Usage==

Line 44:

<source lang="java">

public interface Predator {

boolean chasePrey(Prey p);

void eatPrey(Prey p);

}

</source>

Line 60:

public class Lion implements Predator {

@Override

public boolean chasePrey(Prey p) {

// programmingProgramming to chase prey p (specifically for a lion)

}

@Override

public void eatPrey(Prey p) {

// programmingProgramming to eat prey p (specifically for a lion)

}

}

</source>

Line 75:

Classes can implement multiple interfaces:

<source lang="Java">

public class Frog implements Predator, Prey { ... }

</source>

Interfaces can share common class methods:

<source lang="Java">

class Animal implements LikesFood, LikesWater {

{ boolean likes() { return true; }

}

</source>

Line 88:

<source lang="Java">

class Animal implements Shares<Boolean>, Shares<Integer> ...

// errorError: repeated interface

</source>

Line 96:

Interfaces can extend several other interfaces, using the same formula as described below. For example,

<source lang="java">

public interface VenomousPredator extends Predator, Venomous {

//interface Interface body

}

</source>

is legal and defines a subinterface. Note how it allows multiple inheritance, unlike classes. Note also that <code>Predator</code> and <code>Venomous</code> may possibly define or inherit methods with the same signature, say <code>kill(Prey p)</code>. When a class implements <code>VenomousPredator</code> it will implement both methods simultaneously.