All Flashcards
What are the differences between explicit and implicit calls to the superclass constructor?
Explicit: uses 'super()', programmer-defined arguments | Implicit: auto-inserted by Java, no-argument constructor
What are the differences between calling 'super()' with arguments and calling it without arguments?
With arguments: calls a specific superclass constructor with matching parameters | Without arguments: calls the no-argument constructor of the superclass
What are the differences between initializing instance variables in a superclass constructor vs. a subclass constructor?
Superclass: initializes inherited variables | Subclass: initializes variables specific to the subclass
What are the differences between the roles of the superclass and subclass constructors in object creation?
Superclass: initializes the inherited state and behavior. Subclass: Extends the superclass and initializes its own state and behavior.
What are the differences between the effects of calling 'super()' and not calling 'super()' in a subclass constructor?
Calling 'super()': ensures superclass initialization | Not calling 'super()': relies on implicit call to no-argument constructor (if it exists), may lead to errors if it doesn't exist.
What are the differences between how constructors are inherited vs. how methods are inherited?
Constructors: are not inherited, must be explicitly called using 'super()' | Methods: are inherited and can be overridden.
What are the differences between the purpose of a constructor in a superclass versus a subclass?
Superclass: initializes the common state of all its subclasses. Subclass: initializes its own state and potentially extends the superclass's state.
What are the differences between the flexibility of explicit vs. implicit superclass constructor calls?
Explicit: allows choosing which superclass constructor to call with specific arguments. Implicit: only calls the no-argument constructor.
What are the differences between the consequences of an exception thrown in a superclass constructor vs. a subclass constructor?
Superclass: can prevent the entire object from being created if not handled. Subclass: can be handled within the subclass, allowing partial object creation or alternative initialization.
What are the differences between the visibility of constructors in superclasses vs. subclasses?
Superclass: determines who can create instances of the superclass directly. Subclass: inherits visibility rules but can only call the superclass constructor through 'super()'.
What is the process of calling a superclass constructor from a subclass?
- Define the subclass constructor. 2. Use the 'super()' keyword as the first statement. 3. Pass the appropriate arguments to 'super()' to match the superclass constructor's parameters.
What is the step-by-step process when a subclass object is created?
- Subclass constructor is called. 2. 'super()' is implicitly/explicitly called. 3. Superclass constructor executes. 4. Superclass instance variables are initialized. 5. Subclass instance variables are initialized. 6. Subclass constructor finishes executing.
What are the steps involved in the implicit call to superclass constructor?
- Subclass constructor is invoked without explicit 'super()'. 2. Java compiler automatically inserts 'super()' as the first line. 3. The no-argument constructor of the superclass is called.
What steps are involved in initializing a subclass using the superclass constructor?
- Define subclass constructor. 2. Call superclass constructor using 'super()'. 3. Initialize subclass-specific variables after the 'super()' call.
What is the process of constructor chaining?
- Subclass constructor calls 'super()'. 2. Superclass constructor executes, potentially calling its own 'super()'. 3. This continues up the inheritance hierarchy until the Object class constructor is called.
What are the steps to determine if a subclass constructor needs to explicitly call 'super()'
- Check if the superclass has a no-argument constructor. 2. If no no-argument constructor exists, an explicit call to 'super()' with appropriate arguments is required.
What steps are involved in handling exceptions during superclass constructor calls?
- If the superclass constructor throws an exception, the subclass constructor must handle it (either catch or declare it). 2. Ensure proper cleanup if an exception occurs during superclass initialization.
What is the process of initializing inherited instance variables using the superclass constructor?
- Pass the necessary values to the 'super()' call. 2. The superclass constructor will then assign these values to the inherited instance variables.
What are the steps to create a subclass constructor that takes parameters for both superclass and subclass instance variables?
- Define the subclass constructor with parameters for both. 2. Call 'super()' with parameters intended for the superclass. 3. Initialize the subclass-specific instance variables.
What is the process of ensuring proper initialization order when using 'super()'
- Always call 'super()' as the first statement. 2. This guarantees that the superclass is initialized before the subclass attempts to use any inherited members.
Why are constructors not inherited?
Constructors are specific to the class they are defined in and are responsible for initializing objects of that class.
What is the purpose of the 'super' keyword in a subclass constructor?
To call the constructor of the superclass, allowing reuse of initialization logic.
What happens if a subclass constructor doesn't explicitly call a superclass constructor?
Java automatically inserts a call to the superclass's no-argument constructor.
Why is it important to call the superclass constructor in a subclass?
To ensure that the superclass's instance variables are properly initialized.
Explain the constructor call chain in Java.
Subclass constructor calls superclass constructor, which may call its superclass constructor, and so on, up to the Object class constructor.
What is the role of the Object class in the constructor call chain?
It is the ultimate superclass, and its constructor is always the first to be called.
How does the 'super' keyword promote code reuse?
It allows subclasses to leverage the initialization logic already defined in the superclass constructor.
What is the significance of calling 'super' as the first statement in a subclass constructor?
It ensures that the superclass is initialized before any subclass-specific initialization takes place.
Explain how instance variables are initialized in a subclass when using 'super'.
Instance variables of the superclass are initialized by the superclass constructor, and subclass-specific instance variables are initialized separately in the subclass constructor.
What is the impact of not properly initializing the superclass when creating a subclass?
It can lead to unexpected behavior or errors due to uninitialized or incorrectly initialized superclass members.