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What does it mean to “program to an interface”?
I keep coming across this term:
Program to an interface.
What exactly does it mean? A real life design scenario would be highly appreciated.
To put it simply, instead of writing your classes in a way that says
I depend on this specific class to do my work
you write it in a way that says
I depend on any class that does this stuff to do my work.
The first example represents a class that depends on a specific concrete implementation to do its work. Inherently, that's not very flexible.
The second example represents a class written to an interface. It doesn't care what concrete object you use, it just cares that it implements certain behavior. This makes the class much more flexible, as it can be provided with any number of concrete implementations to do its work.
As an example, a particular class may need to perform some logging. If you write the class to depend on a TextFileLogger, the class is forever forced to write out its log records to a text file. If you want to change the behavior of the logging, you must change the class itself. The class is tightly coupled with its logger.
If, however, you write the class to depend on an ILogger interface, and then provide the class with a TextFileLogger, you will have accomplished the same thing, but with the added benefit of being much more flexible. You are able to provide any other type of ILogger at will, without changing the class itself. The class and its logger are now loosely coupled, and your class is much more flexible.
An interface is a collection of related methods, that only contains the signatures of those methods - not the actual implementation.
If a class implements an interface (class Car implements IDrivable) it has to provide code for all signatures defined in the interface.
Basic example:
You have to classes Car and Bike. Both implement the interface IDrivable:
interface IDrivable
{
void accelerate();
void brake();
}
class Car implements IDrivable
{
void accelerate()
{ System.out.println("Vroom"); }
void brake()
{ System.out.println("Queeeeek");}
}
class Bike implements IDrivable
{
void accelerate()
{ System.out.println("Rattle, Rattle, ..."); }
void brake()
{ System.out.println("..."); }
}
Now let's assume you have a collection of objects, that are all "drivable" (their classes all implement IDrivable):
List<IDrivable> vehicleList = new ArrayList<IDrivable>();
list.add(new Car());
list.add(new Car());
list.add(new Bike());
list.add(new Car());
list.add(new Bike());
list.add(new Bike());
If you now want to loop over that collection, you can rely on the fact, that every object in that collection implements accelerate():
for(IDrivable vehicle: vehicleList)
{
vehicle.accelerate(); //this could be a bike or a car, or anything that implements IDrivable
}
By calling that interface method you are not programming to an implementation but to an interface - a contract that ensures that the call target implements a certain functionality.
The same behavior could be achieved using inheritance, but deriving from a common base class results in tight coupling which can be avoided using interfaces.
Polymorphism depends on programming to an interface, not an implementation.
There are two benefits to manipulating objects solely in terms of the interface defined by abstract classes:
Clients remain unaware of the specific types of objects they use, as long as the objects adhere to the interface that clients expect.
Clients remain unaware of the classes that implement these objects. Clients only know about the abstract class(es) defining the interface.
This so greatly reduces implementation dependencies between subsystems that it leads to this principle of programming to an interface.
See the Factory Method pattern for further reasoning of this design.
Source: "Design Patterns: Elements of Reusable Object-Oriented Software" by G.O.F.
Also See: Factory Pattern. When to use factory methods?
Real-world examples are applenty. One of them:
For JDBC, you are using the interface java.sql.Connection. However, each JDBC driver provides its own implementation of Connection. You don't have to know anything about the particular implementation, because it conforms to the Connection interface.
Another one is from the java collections framework. There is a java.util.Collection interface, which defines size, add and remove methods (among many others). So you can use all types of collections interchangeably. Let's say you have the following:
public float calculateCoefficient(Collection collection) {
return collection.size() * something / somethingElse;
}
And two other methods that invoke this one. One of the other methods uses a LinkedList because it's more efficient for it's purposes, and the other uses a TreeSet.
Because both LinkedList and TreeSet implement the Collection interface, you can use only one method to perform the coefficient calculation. No need to duplicate your code.
And here comes the "program to an interface" - you don't care how exactly is the size() method implemented, you know that it should return the size of the collection - i.e. you have programmed to the Collection interface, rather than to LinkedList and TreeSet in particular.
But my advice is to find a reading - perhaps a book ("Thinking in Java" for example) - where the concept is explained in details.
Every object has an exposed interface. A collection has Add, Remove, At, etc. A socket may have Send, Receive, Close and so on.
Every object you can actually get a reference to has a concrete implementation of these interfaces.
Both of these things are obvious, however what is somewhat less obvious...
Your code shouldn't rely on the implementation details of an object, just its published interface.
If you take it to an extreme, you'd only code against Collection<T> and so on (rather than ArrayList<T>). More practically, just make sure you could swap in something conceptually identical without breaking your code.
To hammer out the Collection<T> example: you have a collection of something, you're actually using ArrayList<T> because why not. You should make sure you're code isn't going to break if, say, you end up using LinkedList<T> in the future.
"Programming to an interface" happens when you use libraries, other code you depend upon in your own code. Then, the way that other code represents itself to you, the method names, its parameters, return values etc make up the interface you have to program to. So it's about how you use third-party code.
It also means, you don't have to care about the internals of the code you depend on, as long as the interface stays the same, your code is safe (well, more or less...)
Technically there are finer details, like language concepts called "interfaces" in Java for example.
If you want to find out more, you could ask what "Implementing an Interface" means...
I think this is one of Erich Gamma's mantras. I can't find the first time he described it (before the GOF book), but you can see it discussed in an interview at: http://www.artima.com/lejava/articles/designprinciples.html
It basically means that the only part of the library which you're going to use you should rely upon is it's API (Application programming interface) and that you shouldn't base your application on the concrete implementation of the library.
eg. Supposed you have a library that gives you a stack. The class gives you a couple of methods. Let's say push, pop, isempty and top. You should write your application relying only on these. One way to violate this would be to peek inside and find out that the stack is implemented using an array of some kind so that if you pop from an empty stack, you'd get some kind of Index exception and to then catch this rather than to rely on the isempty method which the class provides. The former approach would fail if the library provider switched from using an array to using some kind of list while the latter would still work assuming that the provider kept his API still working.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
What does it mean to “program to an interface”?
I keep coming across this term:
Program to an interface.
What exactly does it mean? A real life design scenario would be highly appreciated.
To put it simply, instead of writing your classes in a way that says
I depend on this specific class to do my work
you write it in a way that says
I depend on any class that does this stuff to do my work.
The first example represents a class that depends on a specific concrete implementation to do its work. Inherently, that's not very flexible.
The second example represents a class written to an interface. It doesn't care what concrete object you use, it just cares that it implements certain behavior. This makes the class much more flexible, as it can be provided with any number of concrete implementations to do its work.
As an example, a particular class may need to perform some logging. If you write the class to depend on a TextFileLogger, the class is forever forced to write out its log records to a text file. If you want to change the behavior of the logging, you must change the class itself. The class is tightly coupled with its logger.
If, however, you write the class to depend on an ILogger interface, and then provide the class with a TextFileLogger, you will have accomplished the same thing, but with the added benefit of being much more flexible. You are able to provide any other type of ILogger at will, without changing the class itself. The class and its logger are now loosely coupled, and your class is much more flexible.
An interface is a collection of related methods, that only contains the signatures of those methods - not the actual implementation.
If a class implements an interface (class Car implements IDrivable) it has to provide code for all signatures defined in the interface.
Basic example:
You have to classes Car and Bike. Both implement the interface IDrivable:
interface IDrivable
{
void accelerate();
void brake();
}
class Car implements IDrivable
{
void accelerate()
{ System.out.println("Vroom"); }
void brake()
{ System.out.println("Queeeeek");}
}
class Bike implements IDrivable
{
void accelerate()
{ System.out.println("Rattle, Rattle, ..."); }
void brake()
{ System.out.println("..."); }
}
Now let's assume you have a collection of objects, that are all "drivable" (their classes all implement IDrivable):
List<IDrivable> vehicleList = new ArrayList<IDrivable>();
list.add(new Car());
list.add(new Car());
list.add(new Bike());
list.add(new Car());
list.add(new Bike());
list.add(new Bike());
If you now want to loop over that collection, you can rely on the fact, that every object in that collection implements accelerate():
for(IDrivable vehicle: vehicleList)
{
vehicle.accelerate(); //this could be a bike or a car, or anything that implements IDrivable
}
By calling that interface method you are not programming to an implementation but to an interface - a contract that ensures that the call target implements a certain functionality.
The same behavior could be achieved using inheritance, but deriving from a common base class results in tight coupling which can be avoided using interfaces.
Polymorphism depends on programming to an interface, not an implementation.
There are two benefits to manipulating objects solely in terms of the interface defined by abstract classes:
Clients remain unaware of the specific types of objects they use, as long as the objects adhere to the interface that clients expect.
Clients remain unaware of the classes that implement these objects. Clients only know about the abstract class(es) defining the interface.
This so greatly reduces implementation dependencies between subsystems that it leads to this principle of programming to an interface.
See the Factory Method pattern for further reasoning of this design.
Source: "Design Patterns: Elements of Reusable Object-Oriented Software" by G.O.F.
Also See: Factory Pattern. When to use factory methods?
Real-world examples are applenty. One of them:
For JDBC, you are using the interface java.sql.Connection. However, each JDBC driver provides its own implementation of Connection. You don't have to know anything about the particular implementation, because it conforms to the Connection interface.
Another one is from the java collections framework. There is a java.util.Collection interface, which defines size, add and remove methods (among many others). So you can use all types of collections interchangeably. Let's say you have the following:
public float calculateCoefficient(Collection collection) {
return collection.size() * something / somethingElse;
}
And two other methods that invoke this one. One of the other methods uses a LinkedList because it's more efficient for it's purposes, and the other uses a TreeSet.
Because both LinkedList and TreeSet implement the Collection interface, you can use only one method to perform the coefficient calculation. No need to duplicate your code.
And here comes the "program to an interface" - you don't care how exactly is the size() method implemented, you know that it should return the size of the collection - i.e. you have programmed to the Collection interface, rather than to LinkedList and TreeSet in particular.
But my advice is to find a reading - perhaps a book ("Thinking in Java" for example) - where the concept is explained in details.
Every object has an exposed interface. A collection has Add, Remove, At, etc. A socket may have Send, Receive, Close and so on.
Every object you can actually get a reference to has a concrete implementation of these interfaces.
Both of these things are obvious, however what is somewhat less obvious...
Your code shouldn't rely on the implementation details of an object, just its published interface.
If you take it to an extreme, you'd only code against Collection<T> and so on (rather than ArrayList<T>). More practically, just make sure you could swap in something conceptually identical without breaking your code.
To hammer out the Collection<T> example: you have a collection of something, you're actually using ArrayList<T> because why not. You should make sure you're code isn't going to break if, say, you end up using LinkedList<T> in the future.
"Programming to an interface" happens when you use libraries, other code you depend upon in your own code. Then, the way that other code represents itself to you, the method names, its parameters, return values etc make up the interface you have to program to. So it's about how you use third-party code.
It also means, you don't have to care about the internals of the code you depend on, as long as the interface stays the same, your code is safe (well, more or less...)
Technically there are finer details, like language concepts called "interfaces" in Java for example.
If you want to find out more, you could ask what "Implementing an Interface" means...
I think this is one of Erich Gamma's mantras. I can't find the first time he described it (before the GOF book), but you can see it discussed in an interview at: http://www.artima.com/lejava/articles/designprinciples.html
It basically means that the only part of the library which you're going to use you should rely upon is it's API (Application programming interface) and that you shouldn't base your application on the concrete implementation of the library.
eg. Supposed you have a library that gives you a stack. The class gives you a couple of methods. Let's say push, pop, isempty and top. You should write your application relying only on these. One way to violate this would be to peek inside and find out that the stack is implemented using an array of some kind so that if you pop from an empty stack, you'd get some kind of Index exception and to then catch this rather than to rely on the isempty method which the class provides. The former approach would fail if the library provider switched from using an array to using some kind of list while the latter would still work assuming that the provider kept his API still working.
List<String> someName = new ArrayList<String>();
ArrayList<String> someName = new ArrayList<String>();
Does it impact anything on performance?
The first one is a List of Objects and the latter one is ArrayList of Objects. Correct me if i am wrong. I got confused because ArrayList implements List Interface.
Why do people declare like this? Does it help in any situtions.
When i am receiving some email address from DB, what is the best way to collect it? List of eMail address Objects????
Finally one unrelated question.... can an interface have two method names with same name and signature and same name with different signature.
The difference between the declarations is more one of style. It is preferable to declare variables using the abstract, rather than the concrete implementation, because you can change the implementation choice later without changing the variable type. For example, you might change the List to use a LinkedList instead.
If you always use the abstract type (interface or abstract class) wherever you can, especially in method signatures, the client code is free to use whatever implementation they prefer. This makes the code more flexible and easier to maintain.
This is true even of variable declarations. Consider this:
public abstract class MyListUsingClass {
private List<String> list;
protected MyListUsingClass(List<String> list) {
this.list = list;
}
...
}
If the variable list was declared as ArrayList, then only ArrayLists would be accepted in the constructor. This would be a poor choice: Always try to let the client code chose the implementations they want to use.
Regarding you last question: Interfaces have the same restrictions for methods as classes do, so yes you can overload methods.
There is no performance impact, because in runtime you are dealing with the same class (ArrayList) in both cases.
They are both lists of Strings. The difference is that the first one is declared as a List but initialized as an ArrayList, which is a more specific type of List.
One instance where it helps is when you use an IDE with context-sensitive suggestions (Eclipse, NetBeans, etc). In the first case, whenever you use the suggestion feature, you will only see the members of the List interface. In the second, you will see all (public) members of ArrayList. In any given programming situation, as long as the more abstract type provides the functionality you need, you want to use that because it makes your code more robust: the more abstract a type is, the less likely it is to change in some future release of the API.
The best way to represent anything always depends on what you intend to use the data for and how much of it there is. Probably a List or a Set of javax.mail.internet.InternetAddress will fit the bill.
An interface can have two methods with the same name only if they have different parameter type signatures. Two methods which both take a single string cannot have the same name even if the parameters have different names, nor can you have two methods with the same name which differ only in return type.
In the first cause you're declaring a var of type list and using an ArrayList as its implementation.
In the second case you're declaring and defining an array list.
The difference is that, using the interface type (as in the first case), you will access only those methods defined in the List interface, and if ArrayList has some specific implementation methods, in order to access them you will need to cast your list to its sub-type (ArrayList).
In the second case, you're using a more specific type, so no cast is needed at all.
Performance - probably not.
Actually they are lists of Strings, not objects. Interfaces is not the point of what is held in Collection
Defining variable of superclass type could be usefull if you would like to make your code independent of concrete list implementation. If someday you would like to change list to LinkedList implementation - this won't be so harmful to all your code
Create new type EMail and store them into some kind of list (e.g. mentioned LinkedList or ArrayList) or just array (EMail[]). If you provide more information - this could be helpful.
edit
2. In both cases they are ArrayList of Strings. The difference is, that in first case you're doing casting to the superclass (losing access to some methods specific to ArrayList)
Does it impact anything on performance? No measurable impact. Your code will be the source of your performance issues, not nano-optimizations like this.
The first one ie s a List of Objects and the latter one is ArrayList of Objects. Correct me if i am wrong. I got confused because ArrayList implements List Interface. Exactly. You can assign a class reference to any of the types that it implements.
Why do people declare like this? Does it help in any situations.The reason you might want to is in case you want to change your implementation to use another concrete class that implements List e.g. LinkedList.
When i am receiving some email address from DB, what is the best way to collect it? List of eMail address Objects? Define "best". Depends on how you'll use them. Strings might be sufficient; perhaps a better abstraction would work for you.
Finally one un related question.... can an interface have two method names with same name and signature and same name with different signature. Interfaces define signatures, not implementation. You can have two interfaces with methods that define the same signature, but there can only be one implementation when you execute. If you have a Cowboy and Artist interfaces, both with void draw() methods, the class that implements both will have to decide what the single implementation will be. There can't be one for Cowboy and another for Artist, because interfaces don't have any notion of implementation.
I have seen that if I have interface named interfaceABC.
Example:
public class ABController extends AbstractCOntroller {
private interfaceABC inter;
I am confused that why we make object from interface not from class that implemented it.
private interfaceABC inter;
i am confused that why we make object from interface not from class that implemented it
We haven't created an object/instance yet. We simply declared a variable to hold it. We don't make objects from interfaces (you have to use a concrete class to do that), but we will often use interface types instead of the actual concrete class for variable declarations, method parameter types, and method return types.
Take this for exmaple:
List<Example> examples = new ArrayList<Example>();
...
public List<Example> getExamples() { return examples; }
Using the interface List here instead of the concrete class ArrayList follows a common best practice: to use interfaces instead of concrete classes whenever possible, e.g. in variable declarations, parameters types, and method return types. The reason this is considered a best practice is:
Using the interface for declarations and for return types hides an implementation detail, making it easier to modify in the future. For example, we may find that the code works better using a LinkedList rather than ArrayList. We can easily make this change in one place now, just where the list is instantiated. This practice is especially key for method parameter types and method return types, so that external users of the class won't see this implementation detail of your class and are free to change it without affecting their code.
By using the interface, it may be clearer to a future maintainer that this class needs some kind of List, but it does not specifically need an ArrayList. If this class relied on some ArrayList-specific property, i.e. it needs to use an ArrayList method, than using ArrayList<Example> examples = ... instead of List<Example> examples = ... may be a hint that this code relies on something specific to an ArrayList.
It may simplify testing/mocking to use the more abstract List than to use the concrete class ArrayList.
We haven't made an object, we've made a reference.
By using a reference to the interface rather than a concrete class, we are free to swap in a different implementation of the interface, with no changes to this code. This improves encapsulation, and also facilitates e.g. testing (because we can use mock objects). See also dependency injection.
This is actually very useful. Take the example that we're using a list.
public class A {
private List<String> list;
public A(List<String> list) {
this.list = list;
}
}
This allows class A to work with all operations defined by the list interface. The class constructing A can now give any implementation without changing the code of class A, hence promoting encapsulation, code reuse, testing etc. For instance:
new A(new ArrayList<String>());
For a private field, it does not really matter too much, as that's an implementation detail anyway. Many people will still on principle use the interface everywhere they can.
On the other hand, protected fields (and of course the parameters of public methods) form an API that becomes much more flexible by using interfaces, because that allows subclasses/clients to choose which implementation class they want to use, even classes they supply themselves and which didn't even exist when the API was created.
Of course, if you have a public set method or constructor that sets the private field, then you have to use the interface type for the field as well.
Imagine a gift-wrapping stall in a shop that has a machine which will wrap any box.
The machine is simply designed and built to wrap a rectangular box, it shouldn't matter whether there's chocolate in the box or a toy car. If it mattered, the machine would quite obviously be flawed.
But even before you get to that stall, you have to buy that gift: so the cashier scans the barcode first. The barcode scanner is another example of the same principle: it will scan anything as long as it has a recognisable barcode on it. A barcode scanner that only scanned newspapers would be useless.
These observations led to the concept of encapsulation in software design, which you can see in action when a class refers to an object by an interface only, and not its concrete class.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
What does it mean to “program to an interface”?
I keep coming across this term:
Program to an interface.
What exactly does it mean? A real life design scenario would be highly appreciated.
To put it simply, instead of writing your classes in a way that says
I depend on this specific class to do my work
you write it in a way that says
I depend on any class that does this stuff to do my work.
The first example represents a class that depends on a specific concrete implementation to do its work. Inherently, that's not very flexible.
The second example represents a class written to an interface. It doesn't care what concrete object you use, it just cares that it implements certain behavior. This makes the class much more flexible, as it can be provided with any number of concrete implementations to do its work.
As an example, a particular class may need to perform some logging. If you write the class to depend on a TextFileLogger, the class is forever forced to write out its log records to a text file. If you want to change the behavior of the logging, you must change the class itself. The class is tightly coupled with its logger.
If, however, you write the class to depend on an ILogger interface, and then provide the class with a TextFileLogger, you will have accomplished the same thing, but with the added benefit of being much more flexible. You are able to provide any other type of ILogger at will, without changing the class itself. The class and its logger are now loosely coupled, and your class is much more flexible.
An interface is a collection of related methods, that only contains the signatures of those methods - not the actual implementation.
If a class implements an interface (class Car implements IDrivable) it has to provide code for all signatures defined in the interface.
Basic example:
You have to classes Car and Bike. Both implement the interface IDrivable:
interface IDrivable
{
void accelerate();
void brake();
}
class Car implements IDrivable
{
void accelerate()
{ System.out.println("Vroom"); }
void brake()
{ System.out.println("Queeeeek");}
}
class Bike implements IDrivable
{
void accelerate()
{ System.out.println("Rattle, Rattle, ..."); }
void brake()
{ System.out.println("..."); }
}
Now let's assume you have a collection of objects, that are all "drivable" (their classes all implement IDrivable):
List<IDrivable> vehicleList = new ArrayList<IDrivable>();
list.add(new Car());
list.add(new Car());
list.add(new Bike());
list.add(new Car());
list.add(new Bike());
list.add(new Bike());
If you now want to loop over that collection, you can rely on the fact, that every object in that collection implements accelerate():
for(IDrivable vehicle: vehicleList)
{
vehicle.accelerate(); //this could be a bike or a car, or anything that implements IDrivable
}
By calling that interface method you are not programming to an implementation but to an interface - a contract that ensures that the call target implements a certain functionality.
The same behavior could be achieved using inheritance, but deriving from a common base class results in tight coupling which can be avoided using interfaces.
Polymorphism depends on programming to an interface, not an implementation.
There are two benefits to manipulating objects solely in terms of the interface defined by abstract classes:
Clients remain unaware of the specific types of objects they use, as long as the objects adhere to the interface that clients expect.
Clients remain unaware of the classes that implement these objects. Clients only know about the abstract class(es) defining the interface.
This so greatly reduces implementation dependencies between subsystems that it leads to this principle of programming to an interface.
See the Factory Method pattern for further reasoning of this design.
Source: "Design Patterns: Elements of Reusable Object-Oriented Software" by G.O.F.
Also See: Factory Pattern. When to use factory methods?
Real-world examples are applenty. One of them:
For JDBC, you are using the interface java.sql.Connection. However, each JDBC driver provides its own implementation of Connection. You don't have to know anything about the particular implementation, because it conforms to the Connection interface.
Another one is from the java collections framework. There is a java.util.Collection interface, which defines size, add and remove methods (among many others). So you can use all types of collections interchangeably. Let's say you have the following:
public float calculateCoefficient(Collection collection) {
return collection.size() * something / somethingElse;
}
And two other methods that invoke this one. One of the other methods uses a LinkedList because it's more efficient for it's purposes, and the other uses a TreeSet.
Because both LinkedList and TreeSet implement the Collection interface, you can use only one method to perform the coefficient calculation. No need to duplicate your code.
And here comes the "program to an interface" - you don't care how exactly is the size() method implemented, you know that it should return the size of the collection - i.e. you have programmed to the Collection interface, rather than to LinkedList and TreeSet in particular.
But my advice is to find a reading - perhaps a book ("Thinking in Java" for example) - where the concept is explained in details.
Every object has an exposed interface. A collection has Add, Remove, At, etc. A socket may have Send, Receive, Close and so on.
Every object you can actually get a reference to has a concrete implementation of these interfaces.
Both of these things are obvious, however what is somewhat less obvious...
Your code shouldn't rely on the implementation details of an object, just its published interface.
If you take it to an extreme, you'd only code against Collection<T> and so on (rather than ArrayList<T>). More practically, just make sure you could swap in something conceptually identical without breaking your code.
To hammer out the Collection<T> example: you have a collection of something, you're actually using ArrayList<T> because why not. You should make sure you're code isn't going to break if, say, you end up using LinkedList<T> in the future.
"Programming to an interface" happens when you use libraries, other code you depend upon in your own code. Then, the way that other code represents itself to you, the method names, its parameters, return values etc make up the interface you have to program to. So it's about how you use third-party code.
It also means, you don't have to care about the internals of the code you depend on, as long as the interface stays the same, your code is safe (well, more or less...)
Technically there are finer details, like language concepts called "interfaces" in Java for example.
If you want to find out more, you could ask what "Implementing an Interface" means...
I think this is one of Erich Gamma's mantras. I can't find the first time he described it (before the GOF book), but you can see it discussed in an interview at: http://www.artima.com/lejava/articles/designprinciples.html
It basically means that the only part of the library which you're going to use you should rely upon is it's API (Application programming interface) and that you shouldn't base your application on the concrete implementation of the library.
eg. Supposed you have a library that gives you a stack. The class gives you a couple of methods. Let's say push, pop, isempty and top. You should write your application relying only on these. One way to violate this would be to peek inside and find out that the stack is implemented using an array of some kind so that if you pop from an empty stack, you'd get some kind of Index exception and to then catch this rather than to rely on the isempty method which the class provides. The former approach would fail if the library provider switched from using an array to using some kind of list while the latter would still work assuming that the provider kept his API still working.