Should a method that implements an interface method be annotated with @Override?
The javadoc of the Override annotation says:
Indicates that a method declaration is intended to override a method declaration in a superclass. If a method is annotated with this annotation type but does not override a superclass method, compilers are required to generate an error message.
I don't think that an interface is technically a superclass. Or is it?
You should use @Override whenever possible. It prevents simple mistakes from being made. Example:
class C {
@Override
public boolean equals(SomeClass obj){
// code ...
}
}
This doesn't compile because it doesn't properly override public boolean equals(Object obj).
The same will go for methods that implement an interface (1.6 and above only) or override a Super class's method.
I believe that javac behaviour has changed - with 1.5 it prohibited the annotation, with 1.6 it doesn't. The annotation provides an extra compile-time check, so if you're using 1.6 I'd go for it.
You should always annotate methods with @Override if it's available.
In JDK 5 this means overriding methods of superclasses, in JDK 6, and 7 it means overriding methods of superclasses, and implementing methods of interfaces. The reason, as mentioned previously, is it allows the compiler to catch errors where you think you are overriding (or implementing) a method, but are actually defining a new method (different signature).
The equals(Object) vs. equals(YourObject) example is a standard case in point, but the same argument can be made for interface implementations.
I'd imagine the reason it's not mandatory to annotate implementing methods of interfaces is that JDK 5 flagged this as a compile error. If JDK 6 made this annotation mandatory, it would break backwards compatibility.
I am not an Eclipse user, but in other IDEs (IntelliJ), the @Override annotation is only added when implementing interface methods if the project is set as a JDK 6+ project. I would imagine that Eclipse is similar.
However, I would have preferred to see a different annotation for this usage, maybe an @Implements annotation.
I would use it at every opportunity. See When do you use Java's @Override annotation and why?
JDK 5.0 does not allow you to use @Override annotation if you are implementing method declared in interface (its compilation error), but JDK 6.0 allows it. So may be you can configure your project preference according to your requirement.
By reading the javadoc in java8, you can find the following at the declaration of interface Override:
If a method is annotated with this annotation type compilers are required to generate an error message unless at least one of the following conditions hold:
So, at least in java8, you should use @Override on an implementation of an interface method.
If a concrete class is not overriding an abstract method, using @Override for implementation is an open matter since the compiler will invariably warn you of any unimplemented methods. In these cases, an argument can be made that it detracts from readability -- it is more things to read on your code and, to a lesser degree, it is called @Override and not @Implement.
Overriding your own methods inherited from your own classes will typically not break on refactorings using an ide. But if you override a method inherited from a library it is recommended to use it. If you dont, you will often get no error on a later library change, but a well hidden bug.
It's not a problem with JDK. In Eclipse Helios, it allows the @Override annotation for implemented interface methods, whichever JDK 5 or 6. As for Eclipse Galileo, the @Override annotation is not allowed, whichever JDK 5 or 6.
If the class that is implementing the interface is an abstract class, @Override is useful to ensure that the implementation is for an interface method; without the @Override an abstract class would just compile fine even if the implementation method signature does not match the method declared in the interface; the mismatched interface method would remain as unimplemented.
The Java doc cited by @Zhao
The method does override or implement a method declared in a supertype
is clearly referring to an abstract super class; an interface can not be called the supertype.
So, @Override is redundant and not sensible for interface method implementations in concrete classes.
For me, often times this is the only reason some code requires Java 6 to compile. Not sure if it's worth it.
The problem with including the @Override is that it makes you think that you forgot to call the super.theOverridenMethod() method, which is very confusing. This should be crystal-clear. Perhaps Java should offer an @Interface to be used here. Oh well, yet another half-assed Java peculiarity...
In java 6 and later versions, you can use @Override for a method implementing an interface.
But, I donot think it make sense: override means you hava a method in the super class, and you are implementing it in the sub class.
If you are implementing an interface, I think we should use @Implement or something else, but not the @Override.
This might be too late answer. But I hope this example would help someone to understand why @override is so important (for a scenario like this)
public interface Restaurant(){
public boolean getBill();
public BigDecimal payAmount();
}
public interface Food() extends Restaurant{
public boolean haveSomeFood();
public boolean drinkWater();
}
public class Hungry() implements Food{
public boolean haveSomeFood(){}
public boolean drinkWater(){}
public boolean getBill(){}
public BigDecimal payAmount(){}
}
In the above example, If I am Hungry, I can have Food from a Restaurant. But if I took out the implementation of Restaurant, I do not have to get a bill and no need to pay the amount!!!!
How?
Food has the keyword extends Restaurant - which
means the class Hungry is also implemented from the interface
Restaurant.@overrideIf there was @override, whenever I am trying to remove the Restaurant interface it will show compilation error.
Note: When you implement an interface, you might not know whether that interface is extended to another interface or can be extended or the inheritance may be removed. So it is always better to use @override keyword
inheritance to model the relationship between food and restaurant at first place? There is another way called composition. We shall never rely on the mighty power of a language to overcome the challenge brought by impotent design –
Innocency Should we @Override an interface's method implementation?. I just wanted to describe why @Override is important. Of course, you are right, food can have from a restaurant or from home or from anywhere!. In my example, the tight coupling between food & restaurant is wrong. Thank you for noticing it (but I already thought about this scenario, didn't want to confuse describing those here) –
Ambrosia Eclipse itself will add the @Override annotation when you tell it to "generate unimplemented methods" during creation of a class that implements an interface.
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