It’s a good idea to use an abstract class when you need to implement mutable state. As an example, the Java Collections Framework includes the AbstractList class, which uses the state of variables.

The following example creates an abstract class to simplify the code. This shows the use of an abstract class that simplifies code by abstracting the redundant IsLogMessageValid code. In this example, ...

When designing applications, it is important to know when to use ... class to define a contract that must be followed by types that extend or implement that interface or abstract class. For ...