Chapter 5: Class Design Flashcards
How can Java support multiple inheritance?
Through the use of interfaces
Does Java support multiple levels of inheritance?
Yes
How can you prevent a class from being extended?
By using the ‘final’ keyword
When extending a class without a no-argument constructor, what do you need to do?
Explicitly call super() with valid arguments for one of the super class’s constructors
T or F. You can execute code in the constructor before calling super()
False
Which is executed first? Parent or child constructor?
Parent
How can you access parent members?
Both ‘this’ and ‘super’ will work for inherited members
What are the requirements for overriding?
Must have the same signature
Child must be at least as accessible as the parent
Child may not throw a checked exception that is new or broader than one thrown by parent method
Return type must be same or subtype of parent return type
T or F. A subclass can have a method with the same name as a private method in the parent class
True
How can you explicitly call the parent’s version of an overridden method?
Using the ‘super’ keyword
What is a hidden static method?
A static method that has been overridden. Both must be static
Which version of a method is called if an overridden method is called on a child object in the parent class?
The child version
Which version of a method is called if a hidden method is called on a child object in the parent class?
The parent version
How do you prevent a static method from being hidden?
Make it ‘final’
What are the rules for defining an abstract method?
No implementation is provided in the class where it’s declared
It cannot be final
It can only be defined in an abstract class or interface
It cannot be private
What is a concrete class?
The first non-abstract class to extend an abstract class
What must a concrete class do?
Must implement all inherited abstract methods
What keyword is used when an interface inherits from another interface?
extends
What keyword is used when an abstract class inherits from an interface?
implements
What are variables assumed to be in an interface?
public static final
What are methods assumed to be in an interface?
public abstract
-Unless they are static
Can an interface be instantiated directly?
No
Can an interface extend a concrete class?
No
T or F. Static methods in interfaces are inherited by classes that implement the interface?
False
How do you call a static method in an interface?
By using the name of the interface class
T or F. You can’t implement two interfaces with the same method name
False. You can implement one of those methods to satisfy both interfaces
-Unless return types are different
What is unique about default methods in comparison to other abstract methods?
They aren’t required to be implemented
They have a method body
If you cast a reference variable to the parent type, can you still access subclass members?
No. You can only access members available to the reference type
If you cast a reference variable to the parent type, can you still access subclass members?
No. You can only access members available to the reference type
When you cast an object to a different type, is it’s type changed in memory?
No
T or F. You must explicitly cast a subclass to superclass
False
T or F. You don’t need to explicitly cast a superclass to a subclass
False
T or F. You may cast to unrelated types
False
What is a virtual method?
A method whose implementation isn’t determined until runtime
