Inheritance Study Questions

What is a superclass and subclass?

A class from where a subclass inherits features is called a superclass. It is also called a base class or parent class. A class that inherits all the members (fields, method, and nested classes) from another class is called a subclass. It is also called a derived class, child class, or extended class.

What is super class and subclass?

A class from where a subclass inherits features is called superclass. It is also called base class or parent class. A class that inherits all the members (fields, method, and nested classes) from other class is called subclass. It is also called a derived class, child class, or extended class.

Write the syntax for creating the subclass of a class?

A subclass can be created by using the "extends" keyword. The syntax for declaring a subclass of class is as follows: class subclassName extends superclassName { // Variables of subclass // Methods of subclass } where class and extends are two keywords.

Which class in Java is superclass of every other class?

In Java, Object class is the superclass of every other class.

What is single inheritance and multi-level inheritance?

When one class is extended by only one class, it is called single level inheritance. In single-level inheritance, we have just one base class and one derived class. A class which is extended by a class and that class is extended by another class forming chain inheritance is called multilevel inheritance.

What is order of calling constructors in case of inheritance?

In case of inheritance, constructors are called from the top to down hierarchy.

Why do we need to use inheritance or what is the purpose of using inheritance?

Inheritance is used for code reusability in Java. Some objects share certain properties and behaviors. By using inheritance, a child class acquires all properties and behaviors of the parent class. It helps to increase the features of a class or method by overriding and achieve runtime polymorphism.

Can a class extend itself?

No, a class cannot extend itself.

How will you prove that the features of Superclass are inherited in Subclass?

Refer to this tutorial: Inheritance in Java with Realtime Example

Which of the following is correct way of inheriting class A by class B? a) class B + class A { } b) class B inherits class A { } c) class B extends A { } d) class B extends class A { }

c

What is Multiple inheritance in Java?

A class that has many superclasses is known as multiple inheritance. In other words, when a class extends multiple classes, it is known as multiple inheritance.

What is Hybrid inheritance in java? How will you achieve it?

A hybrid inheritance in java is a combination of single and multiple inheritance. It can be achieved through interfaces.

How is Inheritance implemented/achieved in Java?

Inheritance can be implemented or achieved by using two keywords: extends: extends is a keyword that is used for developing the inheritance between two classes and two interfaces. implements: implements keyword is used for developing the inheritance between a class and interface.

How is Inheritance implemented or achieved in Java?

Inheritance can be implemented or achieved by using two keywords: "extends" is used for developing the inheritance between two classes and "implements" is used for developing the inheritance between a class and an interface.

What is Inheritance in Java?

Inheritance in Java is the technique of creating a new class by using an existing class functionality. It is a process where a child class acquires all the properties and behaviors of the parent class.

Why do we need to use inheritance?Or, What is the purpose of using inheritance?

Inheritance is one of the main pillars of OOPs concept. Some objects share certain properties and behaviors. By using inheritance, a child class acquires all properties and behaviors of parent class. There are the following reasons to use inheritance in java: We can reuse the code from the base class. Using inheritance, we can increase features of class or method by overriding. Inheritance is used to use the existing features of class. It is used to achieve runtime polymorphism i.e method overriding.

What is Is-A relationship in Java?

Is-A relationship represents Inheritance in Java. It is implemented using the "extends" keyword and is used for code reusability.

What is Is-A relationship in Java?

Is-A relationship represents Inheritance. It is implemented using the "extends" keyword. It is used for code reusability.

How does Multiple inheritance implement in Java?

Multiple inheritance can be implemented in Java by using interfaces. A class cannot extend more than one class but a class can implement more than one interface.

Why multiple inheritance is not supported in java through class?

Multiple inheritance means that one class extends two superclasses or base classes but in Java, one class cannot extend more than one class simultaneously. At most, one class can extend only one class. Therefore, to reduce ambiguity, complexity, and confusion, Java does not support multiple inheritance through classes. For more detail, go to this tutorial: Types of Inheritance in Java

Can we extend (inherit) final class?

No, a class declared with final keyword cannot be inherited.

Can a final method be overridden?

No, a final method cannot be overridden.

Are constructor and instance initialization block inherited to subclass?

No, constructor and instance initialization block of the superclass cannot be inherited to its subclass but they are executed while creating an object of the subclass.

Can a class extend more than one class?

No, one class can extend only a single class.

Will this code compile successfully? If yes, what is the output? If no, identify the errors. package pack1; public class A { private int x = 50; protected int y = 100; int z = 200; } package pack2; import pack1.A; public class B extends A { } import pack2.B; public class Test { public static void main(String[] args) { B b = new B(); System.out.println(b.x); System.out.println(b.y); System.out.println(b.z); } }

No, the code will not compile successfully because of two compile-time errors. First error is in line System.out.println(b.x); because private members cannot be accessed in the subclass. Second error is in line System.out.println(b.y); because default members of superclass can be accessed in the subclass within the same package only.

Can we access subclass members if we create an object of superclass?

No, we can access only superclass members but not the subclass members.

Can we assign superclass to subclass?

No.

Can we inherit private members of base class to its subclass?

No.

Is interface inherited from the Object class?

No.

What happens if both superclass and subclass have a field with the same name?

Only subclass members are accessible if an object of subclass is instantiated.

Are static members inherited to subclass in Java?

Static block cannot be inherited to its subclass. A static method of superclass is inherited to the subclass as a static member and non-static method is inherited as a non-static member only.

What is the output of executing code of class Test? public class A { void m1() { System.out.println("m1 in class A"); } } public class B extends A { void m1() { System.out.println("m1 in class B"); } } public class Test { public static void main(String[] args) { B b = new B(); b.m1(); A a = new A(); a.m1(); A a2 = new B(); a2.m1(); } }

The result is m1 in class B, m1 in class A, m1 in class B.

What is Inheritance in Java?

The technique of creating a new class by using an existing class functionality is called inheritance in Java. In other words, inheritance is a process where a child class acquires all the properties and behaviors of the parent class.

What are the various forms of inheritance available in Java?

The various forms of inheritance to use are single inheritance, hierarchical inheritance, and multilevel inheritance.

What are the types of inheritance in Java?

The various types of inheritance are as follows: a. Single inheritance b. Multi-level inheritance c. Hierarchical inheritance d. Multiple inheritance e. Hybrid inheritance

What are the advantages of inheritance in Java?

We can minimize the length of duplicate code in an application by putting the common code in the superclass and sharing it amongst several subclasses. Due to reducing the length of code, the redundancy of the application is also reduced. Inheritance can also make application code more flexible to change.

How will you restrict a member of a class from inheriting its subclass?

We can restrict members of a class by declaring them private because the private members of superclass are not available to the subclass directly. They are only available in their own class.

Will the code successfully compiled? If yes, what is the output? public class A { int x = 20; } public class B extends A { int x = 30; } public class Test { public static void main(String[] args) { B b = new B(); System.out.println(b.x); A a = new A(); System.out.println(a.x); A a2 = new B(); System.out.println(a2.x); } }

Yes, code will be successfully compiled. The output is 30, 20, 20.

Will this code run successfully? If yes, what will be the output? public class A { private int x = 50; void m1() { System.out.println(x); } } public class B extends A { } public class Test { public static void main(String[] args) { A a = new B(); a.m1(); } }

Yes, code will be successfully compiled. The output will be 50.

Can we access both superclass and subclass members if we create an object of subclass?

Yes, we can access both superclass and subclass members.

Which keyword do you use to define a subclass? Or, which keyword is used to inherit a class?

extends keyword.