When default methods were introduced in Java 8, some developers thought they would be the same as abstract classes. That’s not true, however, because interfaces can’t have state.

Abstract classes are used in all object-oriented languages, including Java, C++, C# and VB.NET. Abstract classes aren't required in programming, but the concept is designed to keep code cleaner and ...

Readers have returned quite a bit of feedback concerning, “Abstract Classes Vs. Interfaces” from April 2001. A recurring request asks to see a complete example of using interfaces and abstract ...

Basically ComponentA depends on ComponentB. To enable unit-testing class ComponentAImpl, the implementation of interface ComponentB must be injected into ComponentAImpl. The Java code below shows the ...