polymorphism + java-visual

The image shows an example of polymorphism in Java. Which of the following methods is called when the area() method is invoked on an object of the Shape class?

• Circle area()
• Triangle area()
• Rectangle area()
• Shape area()

Answer explanation

The correct answer is 4. Shape area(). The area() method is defined in the Shape class, and it is overridden by the Circle area(), Triangle area(), and Rectangle area() methods in the respective subclasses. When the area() method is invoked on an object of the Shape class, the overridden method in the specific subclass is called. In this case, the area() method is not overridden in the Shape class, so the Shape area() method is called.

Which of the following statements is true about the parent class and child classes in the image

• The parent class has the deposit() and withdraw() methods, but the child classes do not.
• The parent class and child classes both have the deposit() and withdraw() methods, but the child classes can override these methods.
• The parent class and child classes both have the deposit() and withdraw() methods, and the child classes cannot override these methods.
• The parent class has the deposit() and withdraw() methods, but the child classes have different methods with the same names.

Answer explanation

The image shows that the parent class has two methods, deposit() and withdraw(). The child classes also have these two methods, but they can override them to provide different implementations. For example, the saving child class might override the deposit() method to add a bonus to the amount deposited.

What is the data type of the gender variable in the Author class?

• String
• char
• int
• float

Answer explanation

The correct answer is 2. char. This is because the gender variable is declared as a char in the image. The char data type is used to store a single character, such as 'm' or 'f'.

What is the Java mascot about to do?

• A. Execute an action.
• B. Punch something.
• C. Wave hello.
• D. Give a speech.

Answer explanation

The answer is supported by the text in the image, which says "Duke is going to punch!". The Java mascot, Duke, is a green, anthropomorphic coffee cup with a punchy expression. The code in the image shows that Duke is a subclass of JavaMascot, which has a method called executeAction(). The executeAction() method in Duke prints out the message "Duke is going to punch!", which indicates that Duke is about to punch something.

Which of the following is the most common type of polymorphism?

• Compile time polymorphism
• Runtime polymorphism
• Method overloading
• Operator overloading

Answer explanation

Runtime polymorphism is the most common type of polymorphism because it allows different objects of a class to respond to the same message in different ways. This is done by overriding methods in the base class. The other types of polymorphism, compile time polymorphism and method overloading, are less common.

Which of the following statements is true about the code in the image?

• A Vehicle object can be added to an ArrayList of Car objects.
• A Car object can be added to an ArrayList of Vehicle objects.
• Only Car objects can be added to an ArrayList of Vehicle objects.
• Only Vehicle objects can be added to an ArrayList of Car objects.

Answer explanation

The code in the image shows that a Vehicle object can be added to an ArrayList of Car objects. This is because Vehicle is the superclass of Car, and so any object of type Vehicle can also be an object of type Car.

Which type of polymorphism is shown in the image?

• Compile-time polymorphism
• Run-time polymorphism
• Ad hoc polymorphism
• Coercion polymorphism

Answer explanation

The image shows the two types of polymorphism in Java: compile-time polymorphism and run-time polymorphism. Compile-time polymorphism is shown in the image with the two boxes labeled "Method Overloading". Run-time polymorphism is shown in the image with the two boxes labeled "Method Overriding".

Which of the following methods is overridden in the Circle class?

• draw()
• getArea()
• setRadius()
• toString()

Answer explanation

The answer is draw(). The draw() method is overridden in the Circle class to draw a circle instead of a square. This can be seen in the image, where the draw() method is declared in both the Shape and Circle classes, but the implementation of the method is different in each class.

Which of the following is the most common type of polymorphism achieved in Java?

• A. Method overloading
• B. Method overriding
• C. Compile-time polymorphism
• D. Runtime polymorphism

Answer explanation

Compile-time polymorphism occurs when the compiler can determine which method to call at compile time. This is typically done by overloading methods, which means having multiple methods with the same name but different parameters. For example, the image shows a class called display that has two methods called disp(). The first disp() method takes a character as a parameter, and the second disp() method takes a class as a parameter. The compiler can determine which disp() method to call based on the type of the argument that is passed to the method.

What is the difference between a method in the Common English Language (CEL) and a method in the Java Programming Language (JPL)?

• In CEL, methods are invoked with the . operator, while in JPL, methods are invoked with the () operator.
• In CEL, methods can be overloaded, while in JPL, methods can only be overridden.
• In CEL, methods can be abstract, while in JPL, methods must be concrete.
• In CEL, methods can be static, while in JPL, methods cannot be static.

Answer explanation

The image shows that the method displayInfo() in the CEL class is invoked with the . operator, while the method displayInfo() in the JPL class is invoked with the () operator. This is a key difference between the two languages.