Java Class Design Flashcards
7 cards from real 1Z0-811 practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Java Class Design flashcards as text
Which keyword prevents a class from being subclassed in Java?
Answer: final
The `final` keyword on a class declaration prevents any other class from extending it.
What is the result of calling a non-static method on a null reference in Java?
Answer: NullPointerException at runtime
Invoking an instance method on a null reference throws NullPointerException at runtime.
Which access modifier makes a member accessible only within its own class?
Answer: private
`private` restricts visibility strictly to the declaring class itself.
Given `class B extends A`, and both define `void print()`, what determines which `print()` runs when called via an `A` reference holding a `B` object?
Answer: The object type (B) — runtime polymorphism
Java uses dynamic dispatch: the actual object type (B) determines which overridden method executes at runtime.
What is the purpose of the `super()` call inside a constructor?
Answer: To call the parent class constructor
`super()` explicitly calls the parent class's constructor and must be the first statement in the child constructor.
Which of the following is true about Java interfaces in Java 11?
Answer: Interfaces can have private methods
Since Java 9, interfaces can have private methods to share helper code between default methods.
What happens if a class implements two interfaces that declare the same default method without overriding it?
Answer: Compilation error due to ambiguity
If a class inherits two conflicting default methods and does not override the method, a compile-time error occurs.