As per this article you access default method in interface A using A.super.foo(); This could be used as follows (assuming interfaces A and C both have default methods foo()) public class ChildClass implements A, C { @Override public void foo() { //you could completely override the default implementations doSomethingElse(); //or manage conflicts between the same … Read more
This compile-time error arises when you try to assign or pass (or convert) a concrete type to an interface type; and the type itself does not implement the interface, only a pointer to the type. Short summary: An assignment to a variable of interface type is valid if the value being assigned implements the interface … Read more
I prefer not to use a prefix on interfaces: The prefix hurts readability. Using interfaces in clients is the standard best way to program, so interfaces names should be as short and pleasant as possible. Implementing classes should be uglier to discourage their use. When changing from an abstract class to an interface a coding … Read more
Use an interface when you want to force developers working in your system (yourself included) to implement a set number of methods on the classes they’ll be building. Use an abstract class when you want to force developers working in your system (yourself included) to implement a set numbers of methods and you want to … Read more
Edit: as of Java 8, lambda expressions are a nice solution as other answers have pointed out. The answer below was written for Java 7 and earlier… Take a look at the command pattern. // NOTE: code not tested, but I believe this is valid java… public class CommandExample { public interface Command { public … Read more
The @ symbol denotes an annotation type definition. That means it is not really an interface, but rather a new annotation type — to be used as a function modifier, such as @override. See this javadocs entry on the subject.
Public Service Announcement: I want to state for the record that I believe traits are almost always a code smell and should be avoided in favor of composition. It’s my opinion that single inheritance is frequently abused to the point of being an anti-pattern and multiple inheritance only compounds this problem. You’ll be much better … Read more
UPDATE: This question was the subject of my blog on May 12th 2011. Thanks for the great question! Suppose you have an interface as you describe, and a hundred classes that implement it. Then you decide to make one of the parameters of one of the interface’s methods optional. Are you suggesting that the right … Read more
if (object is IBlah) or IBlah myTest = originalObject as IBlah if (myTest != null)
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 … Read more