Online assessment with HackerRank, featuring 5 questions on Java/OOP and 3 programming questions. Generally not difficult, but they require some thinking. The last question tends to be a bit tricky, but it doesn't necessarily involve dynamic programming (DP).

OOP related: Abstract Class/Abstract Methods in Java

An abstract class in Java is a class that cannot be instantiated on its own. It's declared using the 'abstract' keyword.

Abstract classes can have:

• Abstract methods: Methods declared without an implementation (no method body). These must be overridden by any concrete subclass.
• Concrete methods: Methods with a full implementation.
• Instance variables.
• Constructors.

Abstract methods are declared using the 'abstract' keyword and end with a semicolon; they do not have a body. They are used to define a contract that subclasses must adhere to.

Key points about abstract classes and methods:

• A class must be declared abstract if it has at least one abstract method.
• If a class extends an abstract class, it must either implement all abstract methods or be declared abstract itself.
• Abstract classes are useful for defining common behavior and structure for a group of related classes.