In this Java 101 tutorial, I’ve explained how interfaces differ from classes, and showed you how to declare, implement, and extend interfaces in your Java programs.

When to use interfaces in Java. Interfaces are very useful for decoupling code and implementing polymorphism.We can see an example in the JDK, with the List interface: ...

In other words, a Java class that supports the SOLID open-closed principle will find use in originally un-envisioned scenarios, and be flexible enough to work with newly created classes, interfaces ...