Podcast
Questions and Answers
What does encapsulation in Java primarily allow an object to do?
What does encapsulation in Java primarily allow an object to do?
- Require all fields to be public
- Change its data freely
- Expose all its internal features
- Hide its data and methods (correct)
Which method is used to change the value of a private field in a class?
Which method is used to change the value of a private field in a class?
- Accessor method
- Setter method (correct)
- Public method
- Constructor
What must you remove from a class to make it immutable?
What must you remove from a class to make it immutable?
- Setter methods (correct)
- Public methods
- Constructor
- Private fields
Which of the following correctly describes a getter method?
Which of the following correctly describes a getter method?
What keyword is typically used to declare instance variables that are encapsulated?
What keyword is typically used to declare instance variables that are encapsulated?
Which statement about immutable classes is false?
Which statement about immutable classes is false?
What is the return type of a setter method?
What is the return type of a setter method?
Which part of a class typically encapsulates its state?
Which part of a class typically encapsulates its state?
What is the primary purpose of encapsulation in Java?
What is the primary purpose of encapsulation in Java?
Which naming convention is correct for a getter method that retrieves a non-boolean property?
Which naming convention is correct for a getter method that retrieves a non-boolean property?
What does the 'extends' keyword signify in a class declaration?
What does the 'extends' keyword signify in a class declaration?
What type of class cannot be extended by any other class?
What type of class cannot be extended by any other class?
What is the default visibility of instance variables in a class without any access modifier?
What is the default visibility of instance variables in a class without any access modifier?
Which statement is true regarding the Object class in Java?
Which statement is true regarding the Object class in Java?
In the context of inheritance, how is the subclass related to its superclass?
In the context of inheritance, how is the subclass related to its superclass?
Which of the following methods would be valid for accessing a private attribute named 'name'?
Which of the following methods would be valid for accessing a private attribute named 'name'?
What is the result of calling the constructor of the Student class?
What is the result of calling the constructor of the Student class?
What does the keyword 'super' do in the context of constructors?
What does the keyword 'super' do in the context of constructors?
What is required for method overriding to occur in a subclass?
What is required for method overriding to occur in a subclass?
How must access level be defined for an overridden method compared to the parent method?
How must access level be defined for an overridden method compared to the parent method?
Which of the following lines would properly instantiate a new Student object?
Which of the following lines would properly instantiate a new Student object?
What will be printed as the output when a Student object is created?
What will be printed as the output when a Student object is created?
What happens if the parent constructor requires a parameter but the child constructor does not provide one?
What happens if the parent constructor requires a parameter but the child constructor does not provide one?
What output will be produced if the Person constructor is modified to output its parameter?
What output will be produced if the Person constructor is modified to output its parameter?
What happens if the parent class does not define a no-argument constructor?
What happens if the parent class does not define a no-argument constructor?
What is the purpose of the super() method in the constructor?
What is the purpose of the super() method in the constructor?
What will happen if a child class does not define any constructors?
What will happen if a child class does not define any constructors?
In what scenario is it not allowed to extend a constructor using super()?
In what scenario is it not allowed to extend a constructor using super()?
What will the compiler do if the first statement in a child class constructor is not a call to the parent constructor?
What will the compiler do if the first statement in a child class constructor is not a call to the parent constructor?
What happens if the child class constructor calls super() with an argument while the parent class lacks a matching constructor?
What happens if the child class constructor calls super() with an argument while the parent class lacks a matching constructor?
What is the purpose of the this()
keyword in the Student class?
What is the purpose of the this()
keyword in the Student class?
What error will occur if a child class constructor does not explicitly call a parent class constructor?
What error will occur if a child class constructor does not explicitly call a parent class constructor?
What is indicated by the error regarding super()
in the context of the Person class?
What is indicated by the error regarding super()
in the context of the Person class?
How does Java handle the absence of a super()
call in a child constructor?
How does Java handle the absence of a super()
call in a child constructor?
What will happen if the Person class is updated to include a no-argument constructor?
What will happen if the Person class is updated to include a no-argument constructor?
In which scenario will a compilation error occur during the instantiation of the Student class?
In which scenario will a compilation error occur during the instantiation of the Student class?
What would be the result of calling the constructor of the Person class directly from the Student constructor?
What would be the result of calling the constructor of the Person class directly from the Student constructor?
Which statement is true regarding the constructors in the given context?
Which statement is true regarding the constructors in the given context?
What happens if the Student class does not define any constructors?
What happens if the Student class does not define any constructors?
What is the effect of calling super(name)
in the Student class constructor?
What is the effect of calling super(name)
in the Student class constructor?
Which scenario is correct regarding the use of super()
in multiple inheritance?
Which scenario is correct regarding the use of super()
in multiple inheritance?
What will happen if the Person class has a no-argument constructor and the Student class does not?
What will happen if the Person class has a no-argument constructor and the Student class does not?
Under what condition will the compiler throw an error regarding constructors?
Under what condition will the compiler throw an error regarding constructors?
What does the Java compiler do if the first statement in a child class constructor is not a call to the parent constructor?
What does the Java compiler do if the first statement in a child class constructor is not a call to the parent constructor?
What occurs when a child class constructor does not provide arguments for a parent class constructor that requires them?
What occurs when a child class constructor does not provide arguments for a parent class constructor that requires them?
Why would a parent class throw an error if the child class constructor does not explicitly define any constructors?
Why would a parent class throw an error if the child class constructor does not explicitly define any constructors?
Study Notes
Encapsulation
- In Java, a class encapsulates both fields (state of an object) and methods (actions of an object).
- Encapsulation means hiding data and methods within a class.
- Accessing private fields can be achieved with public methods, such as getter (accessor) and setter (mutator) methods.
- The benefits of encapsulation include reusable programs and restricted access to object features.
- Setter methods begin with "set" and take an argument to set the field value, like
public void setName(String name)
. - Getter methods begin with "get" (or "is" if the property is a boolean) and return the field value, like
public String getName()
.
Immutable Classes
- Immutable classes remain unchanged after an object is created.
- To make a class immutable:
- Remove setter methods.
- Set the values in the constructor.
- Example:
- A
Student
class with a privatename
field can be made immutable by only providing a constructor that receives thename
and agetName()
method. - No setter method
setName()
should be provided.
- A
Inheritance
- Inheritance enables classes to acquire attributes and behaviors from a parent class (superclass, base class).
- The subclass (derived class, child class) inherits from the superclass.
- All Java classes inherit from the
java.lang.Object
class. - To prevent inheritance, mark a class with the
final
modifier. - Even with public access, private fields of a superclass cannot be accessed by its subclass directly.
- Multiple Inheritance (extending from multiple classes) is not allowed in Java.
Constructors and Inheritance
- Java invisibly adds a no-argument (
super()
) constructor to a class if one is not declared. - The
super()
call must be the first statement in the constructor (unless it's a call to another constructor in the same class usingthis()
). - If the parent class does not have a no-argument constructor, the child class must provide a constructor with an explicit
super()
call to a parent constructor. - If a child class constructor doesn't have a
super()
call, the compiler will call the parent class's no-argument constructor, which might not exist leading to a compile error.
Method Overriding
- You can redefine a method in a child class (method overriding), inheriting the definition from the parent class but changing its implementation.
- To override a method, the method in the child class must have the same name, parameter list, and return type as the method in the parent class.
- The overridden method in the child class must have at least as much accessibility as the method in the parent class.
- Parent constructors are always executed before child constructors.
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Description
Explore the concepts of encapsulation and immutable classes in Java. This quiz covers the definition of encapsulation, the use of getter and setter methods, and the principles of constructing immutable classes. Test your knowledge on how these concepts enhance object-oriented programming.