MCQs On Class 21
Object-Oriented Programming (OOP) - Part 3
Part 1: Basic Concepts of Constructors and Destructors
- What is a constructor in PHP?
- A) A function to print values
- B) A function to initialize object properties
- C) A function to end the object lifecycle
- D) A function to handle exceptions
Answer: B - What symbol is used for defining a constructor in PHP?
- A) __construct
- B) __init
- C) constructor
- D) init
Answer: A - In PHP, what symbol is used to define a destructor?
- A) __delete
- B) __destroy
- C) __destruct
- D) destruct
Answer: C - Which of the following statements about constructors is true?
- A) They can only be called explicitly.
- B) They initialize object properties.
- C) They destroy object properties.
- D) They are not part of PHP.
Answer: B - Which of the following statements about destructors is true?
- A) They are used to print values.
- B) They initialize object properties.
- C) They clean up resources.
- D) They create new properties.
Answer: C - What is the primary purpose of a destructor in PHP?
- A) To initialize object properties
- B) To destroy the PHP interpreter
- C) To perform cleanup tasks
- D) To declare variables
Answer: C - How many constructors can a PHP class have?
- A) Only one
- B) Two
- C) Unlimited
- D) None
Answer: A - How many destructors can a PHP class have?
- A) Only one
- B) Two
- C) Unlimited
- D) None
Answer: A - What keyword is used to call the constructor of the parent class in PHP?
- A) super
- B) this
- C) parent
- D) construct
Answer: C - What keyword is used to refer to the current instance of the class in PHP?
- A) this
- B) parent
- C) self
- D) construct
Answer: A
Part 2: Constructor and Destructor Usage
- Which PHP method is automatically called when an object is created?
- A) __construct
- B) initialize
- C) __init__
- D) start
Answer: A - Which PHP method is automatically called when an object is destroyed?
- A) destroy
- B) __destruct
- C) terminate
- D) end
Answer: B - Can constructors in PHP accept parameters?
- A) No
- B) Yes, but only one parameter
- C) Yes, multiple parameters are allowed
- D) Only optional parameters
Answer: C - What happens when an object with a destructor is unset in PHP?
- A) The destructor is called automatically
- B) The destructor is ignored
- C) PHP throws an error
- D) The destructor must be called manually
Answer: A - What is the role of the unset function in relation to destructors?
- A) It skips the destructor
- B) It ends the PHP script
- C) It triggers the destructor
- D) It calls the constructor
Answer: C - In PHP, what is the output if an error occurs during destructor execution?
- A) An exception is thrown
- B) The destructor is terminated
- C) A warning message is shown
- D) The destructor ignores the error
Answer: C - If a PHP class does not have a destructor, what happens when the object is destroyed?
- A) PHP shows an error
- B) PHP calls a default destructor
- C) PHP automatically calls the constructor
- D) PHP does nothing
Answer: B - In PHP, can a constructor return a value?
- A) Yes
- B) No
- C) Only if it is numeric
- D) Only if it is a string
Answer: B - What is the purpose of the parent::__construct in PHP?
- A) To define a default constructor
- B) To call the parent class's constructor
- C) To call a static function
- D) To destroy the object
Answer: B - When a PHP object is destroyed, which of the following occurs first?
- A) Properties are deleted
- B) Destructor is called
- C) Object is reset
- D) Class variables are deleted
Answer: B
Part 3: Constructor and Destructor in Inheritance
- If a child class does not define a constructor, what happens?
- A) The parent constructor is called
- B) PHP throws an error
- C) A default constructor is used
- D) The child class fails to initialize
Answer: A - Can a child class in PHP override the parent constructor?
- A) Yes
- B) No
- C) Only if the constructor has no parameters
- D) Only if the constructor is private
Answer: A - Which of these can replace the constructor in a child class if parent::__construct is not called?
- A) A default PHP constructor
- B) A manually defined constructor
- C) A static function
- D) An exception
Answer: B - Can a parent constructor be called explicitly from a child class in PHP?
- A) Yes, using parent::__construct()
- B) No, it’s automatically called
- C) Only if it's a static method
- D) Only if parameters are omitted
Answer: A - In PHP, what will happen if both parent and child classes have destructors?
- A) Only the child destructor is called
- B) Both destructors are called
- C) PHP throws an error
- D) Only the parent destructor is called
Answer: B
Part 4: Inheritance and Constructor/Destructor Relationships
- What keyword in PHP allows a class to inherit the constructor of its parent class?
- A) inherit
- B) extends
- C) implements
- D) constructor
Answer: B - If a class does not have a constructor and it inherits from a parent class with a constructor, what happens?
- A) PHP ignores the parent constructor
- B) PHP automatically calls the parent constructor
- C) PHP throws an error
- D) PHP creates a default constructor
Answer: B - If a child class has its own constructor, what must you do to also call the parent constructor?
- A) Use parent::__construct()
- B) Use this::parent()
- C) Use __construct()
- D) No additional steps are needed
Answer: A - In PHP, can you have both a parent and a child destructor in a class hierarchy?
- A) No, only one is allowed
- B) Yes, both can be defined and called
- C) Yes, but only the child destructor is used
- D) No, only the parent destructor is used
Answer: B - What will happen if a child class in PHP does not call the parent destructor?
- A) The parent destructor is ignored
- B) PHP automatically calls it
- C) PHP throws an error
- D) Only the child destructor is executed
Answer: B
Part 5: Constructor Overloading
- Which of the following is true about constructor overloading in PHP?
- A) PHP supports multiple constructors with different parameters
- B) Only one constructor is allowed per class
- C) PHP automatically selects a constructor based on arguments
- D) Constructor overloading is required in PHP
Answer: B - How can constructor overloading be simulated in PHP?
- A) By defining multiple constructors
- B) By using default arguments in a single constructor
- C) By defining a method called __construct2
- D) Constructor overloading is not possible in PHP
Answer: B - If a PHP constructor accepts default values, how many arguments can be passed?
- A) Exactly one
- B) Only as many as the default values allow
- C) It varies based on parameters passed
- D) All arguments must be specified
Answer: C - What is the advantage of using default values in constructors in PHP?
- A) It prevents errors
- B) It allows flexibility in instantiating objects
- C) It restricts constructor usage
- D) It simplifies inheritance
Answer: B - What happens if a child class does not define a constructor but the parent class has one with parameters?
- A) An error occurs
- B) The child must pass arguments during instantiation
- C) The constructor is ignored
- D) PHP uses default values
Answer: B
Part 6: Destructor Behavior and Lifecycle
- Which of the following is true about destructors?
- A) Destructors are called when the script finishes
- B) Destructors must be manually called
- C) Destructors cannot free resources
- D) Destructors are used to define class properties
Answer: A - When does the destructor run in a PHP script?
- A) Immediately after the constructor
- B) When the object is no longer referenced
- C) Before the constructor
- D) When explicitly called
Answer: B - What happens if you try to use unset() on an object without a destructor in PHP?
- A) PHP throws an error
- B) The object is destroyed without cleanup
- C) PHP creates a destructor automatically
- D) The object stays in memory
Answer: B - If a destructor in PHP has side effects, which of the following is true?
- A) It should be avoided
- B) It must be explicitly logged
- C) It will execute even if an error occurs
- D) It is skipped during exceptions
Answer: C - In which situation might a PHP destructor be skipped?
- A) During memory cleanup
- B) If the script terminates unexpectedly
- C) If it lacks side effects
- D) During object initialization
Answer: B
Part 7: Practical Application and Examples
- Why might you use a constructor in a PHP class?
- A) To set initial values for properties
- B) To override methods
- C) To destroy the class instance
- D) To close the PHP script
Answer: A - What is a common use for a destructor in PHP?
- A) Logging object deletion
- B) Resetting properties
- C) Initializing object properties
- D) Fetching new data
Answer: A - When should you call a destructor explicitly in PHP?
- A) Never; destructors are called automatically
- B) At the start of the script
- C) Right after the constructor
- D) When you need to create a new object
Answer: A - If a class has a constructor but no destructor, what happens when the object is destroyed?
- A) PHP throws an error
- B) PHP automatically cleans up
- C) PHP skips the destructor
- D) PHP creates a default destructor
Answer: B - Can a PHP constructor call another method within the class?
- A) Yes
- B) No
- C) Only if it’s static
- D) Only if it’s private
Answer: A
Part 8: Special Cases and Error Handling
- What happens if a destructor contains an error?
- A) PHP ignores it
- B) PHP terminates the script
- C) PHP shows a warning and continues
- D) PHP skips other destructors
Answer: C - What will happen if a destructor throws an exception in PHP?
- A) PHP terminates the script
- B) PHP ignores the exception
- C) PHP converts it to a warning
- D) PHP handles it and continues
Answer: A - Is it possible for a constructor to fail in PHP?
- A) Yes, if there is an error in the code
- B) No, constructors cannot fail
- C) Only if the destructor also fails
- D) Only if PHP version is outdated
Answer: A - What function can be used to handle exceptions in constructors?
- A) try-catch
- B) finally
- C) throw
- D) unset()
Answer: A - Can you directly call __destruct()?
- A) Yes
- B) No, destructors are automatic
- C) Only if the destructor is public
- D) Only with specific classes
Answer: B
Part 9: Real-World Applications
- In a database connection class, how would you typically use a constructor?
- A) To execute queries
- B) To establish a connection to the database
- C) To close the connection
- D) To handle errors
Answer: B - Why might a destructor be useful in a database connection class?
- A) To log queries
- B) To close the database connection
- C) To initialize the connection
- D) To handle user input
Answer: B - In a logging class, what would be a good use for a constructor?
- A) To set up log file paths
- B) To write log entries
- C) To format log messages
- D) To display logs to the user
Answer: A - What could be a potential drawback of using destructors to handle important cleanup tasks?
- A) They are executed automatically
- B) They might not run if the script exits unexpectedly
- C) They can be called multiple times
- D) They cannot handle exceptions
Answer: B - How can you ensure that a destructor runs in a PHP web application?
- A) Use exit() at the end of the script
- B) Avoid using die() in the script
- C) Make sure the object remains in scope
- D) Always use unset() before the end of the script
Answer: C
Part 10: Common Scenarios and Pitfalls
- What will happen if you try to use an object after it has been destructed?
- A) PHP will recreate the object
- B) It will cause an error
- C) The object will still be accessible
- D) PHP ignores the object
Answer: B - Which method would you use to handle multiple resources within a class in PHP?
- A) A single destructor for cleanup
- B) Multiple constructors
- C) Separate methods for each resource
- D) Use static methods
Answer: A - When is the best time to implement cleanup code in your PHP classes?
- A) In the constructor
- B) In the destructor
- C) At the start of the script
- D) Inside methods
Answer: B - If you have multiple objects of a class, when will the destructor be called for each object?
- A) At the end of the script
- B) When the object goes out of scope
- C) Only when explicitly called
- D) Immediately after instantiation
Answer: B - What will happen if a class has a constructor that accepts parameters, but you instantiate it without parameters?
- A) An error occurs
- B) PHP uses default values
- C) The constructor is ignored
- D) It creates a new object
Answer: A
Part 11: Testing and Debugging
- How can you check if a destructor was called in PHP?
- A) Use print statements
- B) Set a flag variable in the destructor
- C) Log the call to a file
- D) All of the above
Answer: D - What should you avoid doing in a destructor to ensure predictable behavior?
- A) Closing files
- B) Calling external APIs
- C) Setting properties
- D) Releasing resources
Answer: B - In debugging a PHP class, what could indicate that a destructor is not functioning as intended?
- A) Memory leaks
- B) Objects not being instantiated
- C) Constructors being skipped
- D) PHP error logs
Answer: A - What PHP function can you use to trigger a destructor manually for debugging?
- A) __destruct()
- B) unset()
- C) die()
- D) exit()
Answer: B - What happens if you forget to call parent::__construct() in a child class?
- A) The parent constructor is called anyway
- B) The child constructor runs but the parent constructor logic is skipped
- C) An error occurs
- D) It works as expected
Answer: B
Part 12: Advanced Topics
- Which of the following can you use to invoke a destructor in an object-oriented design?
- A) By directly calling the destructor
- B) By using unset() on the object
- C) By calling a method within the class
- D) None of the above
Answer: B - What will happen to a destructor if you have a circular reference in PHP?
- A) The destructor will be called multiple times
- B) The destructor may not run
- C) PHP will automatically resolve the reference
- D) An error will be thrown
Answer: B - In which scenario would you need to override a destructor?
- A) When changing variable types
- B) When managing a different resource than the parent
- C) If the constructor has changed
- D) It is never necessary to override destructors
Answer: B - Can you have static properties or methods in a destructor in PHP?
- A) Yes, but not common practice
- B) No, destructors cannot handle static properties
- C) Yes, it is recommended
- D) It is mandatory
Answer: A - When dealing with exception handling in constructors and destructors, which is true?
- A) Only constructors can throw exceptions
- B) Destructors cannot throw exceptions
- C) Both can throw exceptions, but it can complicate cleanup
- D) Exceptions are ignored in destructors
Answer: C
Part 13: Best Practices
- What is the best practice regarding destructors in PHP?
- A) Always use them
- B) Avoid using them unless necessary
- C) Use them for all classes
- D) Only use them in complex applications
Answer: B - In which of the following situations would a destructor be particularly useful?
- A) Managing database connections
- B) Performing calculations
- C) Displaying output to users
- D) Handling exceptions
Answer: A - How should you handle resources in a destructor?
- A) Release them immediately
- B) Check if they are already released
- C) Log the release
- D) You should never handle resources in a destructor
Answer: B - When designing a class with a destructor, what should you consider?
- A) The potential for circular references
- B) Whether resources are released properly
- C) The timing of object destruction
- D) All of the above
Answer: D - Which of the following is a common mistake when using destructors?
- A) Forgetting to log events
- B) Trying to access resources that may have already been released
- C) Not using a destructor at all
- D) Calling destructors explicitly
Answer: B
Part 14: Additional Concepts
- What is a "finalizer" in the context of PHP?
- A) A type of destructor
- B) A method that runs before a constructor
- C) A method that cleans up resources
- D) A deprecated feature in PHP
Answer: A - What does the self keyword refer to in a PHP class?
- A) The current instance of the class
- B) The parent class
- C) The class itself
- D) All instantiated objects
Answer: C - In which of the following scenarios should you be cautious about using destructors?
- A) When managing static properties
- B) In long-running scripts
- C) In web applications with short execution times
- D) Both A and C
Answer: D - What is the primary role of a constructor?
- A) To destruct the class
- B) To initialize the object
- C) To release resources
- D) To call other methods
Answer: B - When writing unit tests for a class with a destructor, what should you ensure?
- A) The destructor is always called
- B) Resources are properly released
- C) The constructor functions correctly
- D) Both A and B
Answer: D
Part 15: Review and Self-Assessment
- How can you improve the reliability of a destructor?
- A) By avoiding complex logic
- B) By logging every action taken
- C) By throwing exceptions
- D) By using only static properties
Answer: A - What is the difference between a destructor and a finalizer?
- A) There is no difference
- B) A destructor is specific to classes; a finalizer is for resources
- C) A finalizer runs before a destructor
- D) A destructor can be called manually; a finalizer cannot
Answer: B - Why is it important to manage memory effectively in PHP?
- A) PHP has unlimited memory
- B) To prevent memory leaks and optimize performance
- C) Memory management is not a concern in PHP
- D) To reduce code complexity
Answer: B - Which design pattern often uses constructors and destructors?
- A) Singleton Pattern
- B) Observer Pattern
- C) Factory Pattern
- D) Strategy Pattern
Answer: A - What should you document when working with constructors and destructors?
- A) Parameters used
- B) Resource allocation
- C) Any exceptions thrown
- D) All of the above
Answer: D
Part 16: Advanced Scenarios
- In what situation would you use a destructor to free external resources?
- A) When using PHP scripts without a database
- B) When connecting to APIs or external services
- C) Only when required by the operating system
- D) It is never required
Answer: B - How can you verify if an object's destructor has been called in a complex application?
- A) By checking the application logs
- B) By using a debugging tool
- C) By setting flags in the destructor
- D) All of the above
Answer: D - What should you consider when designing a class hierarchy with constructors and destructors?
- A) Proper chaining of constructors
- B) Consistent behavior of destructors across classes
- C) Resource management in the hierarchy
- D) All of the above
Answer: D - Can a destructor be inherited in PHP?
- A) Yes, it can be overridden
- B) No, destructors cannot be inherited
- C) Yes, but only in abstract classes
- D) No, they must be defined in each class
Answer: A - How does PHP handle object destruction at the end of a script execution?
- A) Automatically calls destructors for all objects
- B) Ignores objects that are out of scope
- C) Runs destructors in a random order
- D) Executes destructors only for global objects
Answer: A
Part 17: Review and Final Assessment
- What is the impact of using a destructor that performs complex logic?
- A) It enhances performance
- B) It can lead to unpredictable behavior
- C) It simplifies code readability
- D) It is generally recommended
Answer: B - What should be your first action when debugging a destructor that doesn’t seem to work?
- A) Check for circular references
- B) Print debugging statements
- C) Review the constructor
- D) All of the above
Answer: D - How can you prevent resource leaks when using destructors?
- A) Regularly check for memory usage
- B) Properly manage and release resources in the destructor
- C) Always use global variables
- D) Avoid using resources altogether
Answer: B - In PHP, what would happen if an object with a destructor goes out of scope?
- A) The destructor will not be called
- B) The destructor will be called automatically
- C) An error will occur
- D) The object is completely removed from memory
Answer: B - Why might you want to log events within a destructor?
- A) To track resource usage
- B) For debugging purposes
- C) To ensure the destructor was executed
- D) All of the above
Answer: D
Part 18: Conclusion and Self-Evaluation
- What is the primary purpose of a destructor in PHP?
- A) To create instances of a class
- B) To initialize class properties
- C) To clean up resources before an object is destroyed
- D) To call other methods
Answer: C - How should you handle exceptions in destructors?
- A) Catch and log them
- B) Throw them again
- C) Ignore them
- D) Convert them to error messages
Answer: A - What can you do if an object does not have a destructor defined?
- A) PHP will automatically manage resources
- B) You cannot instantiate the object
- C) You should manually release resources
- D) An error will occur
Answer: A - How can inheritance affect the behavior of constructors and destructors?
- A) Child classes must define their own constructors
- B) Parent class destructors are automatically inherited
- C) Child classes can override parent constructors
- D) Both B and C
Answer: D - What is the key takeaway regarding the use of constructors and destructors in PHP?
- A) They are optional for every class
- B) They are critical for proper resource management
- C) Only constructors are important
- D) Destructors are only used in complex applications
Answer: B