Inheritance Example Program in Java for Practice

In this tutorial, we have listed topic-wise the best collection of inheritance example program in Java with output and explanation.

These inheritance example programs are very important for Java interview purposes and technical test.

If you practice all these interview programs, then definitely, you can able to solve all questions based on Java inheritance . So, let’s start with simple program for practice.

Single Level Inheritance Program in Java

Let’s take a simple example program based on single inheritance in Java. In this example, we will create only one superclass and one subclass that will inherit instance method methodA() from the superclass. Look at the program code to understand better.

Program code 1:

Explanation:

In this example, we have defined a base class A which contains a single methodA() method. The statement “class B extends A” tells Java compiler that B is a new class inheriting from class A. This makes class A as the base class of class B and class B is known as a derived class.

In subclass B, we have defined one method methodB(). Subclass B contains inherited members ( methodA() ) of base class A and methodB(). In the main method, we have created an object of class B and invoked methods methodA() which is inherited from class A and methodB().

Multilevel Inheritance Program in Java

Let’s take a simple example program based on the multilevel inheritance in Java. Look at the program code and explanation.

Program code 2:

In this example, we have defined a class X which is a parent class (or base class) for class Y (child class). Class Y is the parent class for class Z (child class).

Thus, class X is the grandfather of class Z (grandchild). The function methodY of class Y is inherited directly from class Y in class Z but the function methodX of class X is inherited indirectly from class X through class Y in class Z.

Hierarchical Inheritance Program in Java

Let’s take a very simple example program in which we will derive multiple subclasses such as B, C, and D from a single superclass A. All subclasses will inherit msgA() method from class A. Look at the program code to understand better.

Program code 3:

Behavior of Instance Variables in case of Inheritance

We know that instance variables are initialized at compile time. When an instance variable of the superclass is the same as that of the child class instance variable name, the “reference type” plays an important role to access instance variable. Let’s take an example program based on this concept.

Program code 4:

1. Inside the main() method, an object of class Q has been created. The reference variable q is pointing to the object of class Q.

2. Variable ‘a’ of Q is called because the reference variable for class Q has been created and is pointing to the object of class Q.

3. P p = new Q(); means the superclass reference variable is declared equal to the child class object.

4. Variable ‘a’ of P is called because, in the main() method, the reference variable for class P has been created but the object is created for the child class whereas, the object is referring itself to the superclass.

As the object is referring to the superclass at compile-time, Java compiler checks whether an instance variable is present or not in superclass.

If the instance variable is present in the superclass at the runtime, it will call the instance variable of the superclass.

Behavior of Overriding Method in case of Inheritance

Let’s take an example program to understand the behavior of overriding methods in the case of inheritance.

Program code 5:

3. When statement obj.msg() will be executed by JVM, msg() method of the child class is called because when any overridden method is called, it completely depends on the object through which it is called and the appropriate method call takes place according to this object. Since the object has been created for the child class, so msg() method of the child class will be called, not of a parent class.

4. The statement “Baseclass obj2 = new Childclass()” implies that the superclass reference variable is declared equal to the child class objects. In other words, the superclass reference variable holds the address of the created subclass objects. The reference variable ‘obj2’ is eligible to call only the members of a superclass.

5. When the statement obj2.msg() will be executed by JVM, msg() method of Childclass is called. This is because the object is created for the child class.

6. When obj2.x will be executed by JVM, variable “x” of Baseclass will be called because obj2 is the reference of Baseclass (superclass).

7. The statement obj2.y; an error will occur because variable “y” does not exist in Baseclass.

8. When obj2.msg(); will be executed, msg() of Childclass will be called because the object has been created for Childclass (subclass).

9. On the execution of obj2.msg2();, an error will occur because msg2() is a newly created method in Childclass. Therefore, we cannot access the newly created method by creating the reference of super class and pointing to the object of subclass.

Let’s take another example program based on the behavior of overriding method in case of inheritance.

Program code 6:

1. Inside the main method,

a. When an object of class Hi will create, the constructor of class Hi will be called immediately. But, the super keyword present in the first line of class Hi will call its parent class Hello. Since the instance block is present in the parent class, it will be executed first before the execution of parent class constructor and calls the show() method.

Since the show() method has been overridden in the child class, therefore, show() method of class Hi will be called. Hence, the output will be “Hi method”.

b. After executing the instance block, the constructor of the parent class will be executed. The output will be “Hello constructor”.

c. Inside the parent class constructor, the show() method of class Hi will be called. So, the output is “Hi method” because the object is created for the child class Hi.

d. After execution of complete parent class constructor, the constructor of Hi (child class) will be called.

2. The show() method of class Hi is called because the object is created for the child class.

3. The output will be the same for lines Hello obj1 = new Hi(); and obj1.show();.

Behavior of Overloaded Method in Inheritance

Method overloading is done at the compile time. Therefore, an appropriate method is invoked according to the reference type to call an overloaded method. Let’s take an example program to clarify this.

Program code 7:

1. The statement Animal a = new Lion(); implies that ‘a’ is the reference of the parent class whereas an object is created for the child class. When a.food(); is executed, food() method is called through the reference type ‘a’.

At the compile-time, the compiler checks the food() signature in the parent class. If the food() method is not overridden in the child class, it will call the parent class method at runtime. That’s why the output is “What kind of food do lions eat?”.

2. When the line a.food(20); is executed, it will give compile-time error. This is because the parent class Animal does not have a food method that takes an integer argument.

3. When the statement l.food(); will be executed, the food() method of class Lion will be called because the reference variable l is a type of Lion that is a subclass. The food() method of Animal class is available in Lion class through inheritance. Therefore, the output is “What kind of food do lions eat?”.

4. When l.food(20); will be executed, the food(int x) method of class Lion will be called. The output is “Lions eat flesh”.

Key Points:

1. At the compile time, an object reference variable plays an important role to call the method.

2. At runtime, the type of object created plays an important role to call the method.

Scenarios Based Program in Inheritance

Consider the below scenarios.

In this example program, we will create a superclass called AA and one subclass of it, called BB. Superclass AA declares two variables x, y, and two methods named msg1(), and msg2(). The subclass overrides one variable y and one method msg2() declared in AA. It also declares one variable z and one method named msg3().

Program code 8:

Only change the below class for all types of below scenarios.

Scenario 1:

In this scenario, there is a class Scenario1. Inside the main() method, an object of class AA is created and calls the variables and methods by using the object reference variable.

Scenario 2: 

Scenario 3:

Scenario 4:

Scenario 5:

Scenario 6:

In this tutorial, we have covered almost all the variety of J ava inheritance example program with explanations that you must practice before going for the technical interview. All the Java inheritance programs are very important for freshers and experienced level interviews. Keep in mind all the above concepts. In the next, we will understand class relationships in Java with the help of examples. Thanks for reading!!!

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Inheritance is one of the key features of OOP that allows us to create a new class from an existing class.

The new class that is created is known as subclass (child or derived class) and the existing class from where the child class is derived is known as superclass (parent or base class).

The extends keyword is used to perform inheritance in Java. For example,

In the above example, the Dog class is created by inheriting the methods and fields from the Animal class.

Here, Dog is the subclass and Animal is the superclass.

Example 1: Java Inheritance

In the above example, we have derived a subclass Dog from superclass Animal . Notice the statements,

Here, labrador is an object of Dog . However, name and eat() are the members of the Animal class.

Since Dog inherits the field and method from Animal , we are able to access the field and method using the object of the Dog .

Subclass Dog can access the field and method of the superclass Animal.

  • is-a relationship

In Java, inheritance is an is-a relationship. That is, we use inheritance only if there exists an is-a relationship between two classes. For example,

  • Car is a Vehicle
  • Orange is a Fruit
  • Surgeon is a Doctor
  • Dog is an Animal

Here, Car can inherit from Vehicle , Orange can inherit from Fruit , and so on.

Method Overriding in Java Inheritance

In Example 1 , we see the object of the subclass can access the method of the superclass.

However, if the same method is present in both the superclass and subclass, what will happen?

In this case, the method in the subclass overrides the method in the superclass. This concept is known as method overriding in Java.

Example 2: Method overriding in Java Inheritance

In the above example, the eat() method is present in both the superclass Animal and the subclass Dog .

Here, we have created an object labrador of Dog .

Now when we call eat() using the object labrador , the method inside Dog is called. This is because the method inside the derived class overrides the method inside the base class.

This is called method overriding. To learn more, visit Java Method Overriding .

Note : We have used the @Override annotation to tell the compiler that we are overriding a method. However, the annotation is not mandatory. To learn more, visit Java Annotations .

super Keyword in Java Inheritance

Previously we saw that the same method in the subclass overrides the method in superclass.

In such a situation, the super keyword is used to call the method of the parent class from the method of the child class.

Example 3: super Keyword in Inheritance

In the above example, the eat() method is present in both the base class Animal and the derived class Dog . Notice the statement,

Here, the super keyword is used to call the eat() method present in the superclass.

We can also use the super keyword to call the constructor of the superclass from the constructor of the subclass. To learn more, visit Java super keyword .

protected Members in Inheritance

In Java, if a class includes protected fields and methods, then these fields and methods are accessible from the subclass of the class.

Example 4: protected Members in Inheritance

In the above example, we have created a class named Animal. The class includes a protected field: name and a method: display() .

We have inherited the Dog class inherits Animal . Notice the statement,

Here, we are able to access the protected field and method of the superclass using the labrador object of the subclass.

  • Why use inheritance?
  • The most important use of inheritance in Java is code reusability. The code that is present in the parent class can be directly used by the child class.
  • Method overriding is also known as runtime polymorphism. Hence, we can achieve Polymorphism in Java with the help of inheritance.
  • Types of inheritance

There are five types of inheritance.

1. Single Inheritance

In single inheritance, a single subclass extends from a single superclass. For example,

Class A inherits from class B.

2. Multilevel Inheritance

In multilevel inheritance, a subclass extends from a superclass and then the same subclass acts as a superclass for another class. For example,

Class B inherits from class A and class C inherits from class B.

3. Hierarchical Inheritance

In hierarchical inheritance, multiple subclasses extend from a single superclass. For example,

Both classes B and C inherit from the single class A.

4. Multiple Inheritance

In multiple inheritance, a single subclass extends from multiple superclasses. For example,

Class C inherits from both classes A and B.

Note : Java doesn't support multiple inheritance. However, we can achieve multiple inheritance using interfaces. To learn more, visit Java implements multiple inheritance .

5. Hybrid Inheritance

Hybrid inheritance is a combination of two or more types of inheritance. For example,

Class B and C inherit from a single class A and class D inherits from both the class B and C.

Here, we have combined hierarchical and multiple inheritance to form a hybrid inheritance.

Table of Contents

  • Introduction
  • Example: Java Inheritance
  • Method Overriding Inheritance
  • super Keyword Inheritance
  • protected Members and Inheritance

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Java Inheritance Quiz Practice Coding Questions

pramodbablad

  • October 25, 2015
  • Java Practice Coding Questions

88 Comments

In this post, there are some 40 Java inheritance quiz type questions and answers which will help you to understand Java inheritance concept better.

Java Inheritance Quiz Practice Coding Questions :

1) Tinku has written the code like below. But, it is showing compile time error. Can you identify what mistake he has done?

2) What will be the output of this program?

Java inheritance quiz

3) What will be the output of the below program?

4) Can a class extend itself?

5) What will be the output of the following program?

6) What will be the output of this program?

7) What will be the output of the below program?

8) Private members of a class are inherited to sub class. True or false?

9) What will be the output of the following program?

10) Below code is showing compile time error. Can you suggest the corrections?

11) What is wrong with the below code? Why it is showing compile time error?

12) You know that compiler will keep super() calling statement implicitly as a first statement in every constructor. What happens if we write this() as a first statement in our constructor?

13) Can you find out the error in the below code?

14) Which class is a default super class for every class in java?

15) Can you find out the error in the below code?

16) What will be the output of this program?

17) What will be the output of the below program?

18) What will be the output of the following program?

19) Why Line 10 in the below code is showing compilation error?

20) What will be the output of the below program?

21) What will be the output of this program?

22) What will be the output of the following program?

23) What happens if both super class and sub class have a field with same name?

24) Does the below program execute successfully? If yes, what will be the output?

25) How do you prevent a field or a method of any class from inheriting to sub classes?

26) What will be the output of the below program?

27) Does java support multiple inheritance?

28) What will be the output of this program?

29) Does the fields with default visibility inherited to sub classes outside the package?

30) Constructors are also inherited to sub classes. True or false?

31) What will be the output of the below program?

32) What happens if both super class and sub class have a field with same name?

33) What will be the output of the below program?

34) What will be the outcome of the following program?

35) Can a class be extended by more than one classes?

36) Does the below program written correctly? If yes, what will be the output?

37) Does the below code prints “Hi….” on the console? If yes, how many times?

38) What value the fields ‘i’ and ‘j’ will hold when you instantiate ‘ClassTwo’ in the below code?

39) When you instantiate a sub class, super class constructor will be also executed. True or False?

40) Does the below code written correctly? If yes, what will be the output?

Also Read :

  • Classes & Objects Quiz
  • Polymorphism Quiz
  • Abstract Classes Quiz
  • Java Interfaces Quiz
  • Java Modifiers Quiz
  • Nested Classes Quiz
  • Java Enums Quiz
  • i++, i– & ++i, –i Quiz
  • Java Arrays Quiz
  • Java Strings Quiz
  • Java Inheritance Oracle Docs
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Q 38 ) pls cross-verify the o/p of Q38. class ClassOne { static int i = 111;

int j = 222;

{ i = i++ – ++j; System.out.println(i); }

class ClassTwo extends ClassOne {

{ j = i– + –j; System.out.println(j); } }

public class MainClass { public static void main(String[] args) { ClassTwo two = new ClassTwo();

o/p- -112 110

Yes, I am also getting the same out put -112 110

in question 38, line number 15; that is j = i– + –j;

value of “i” will get decremented from -112 to -113 so the final value of i is -113

in question 38, line number 15; that is j = i– + –j;

value of “i” will get same value 111(i-) + (-j) j value will get decremented 221 so the final value is 332

class ClassOne { static int i = 111; int j = 222; { i = i++ – ++j; // i = 111(increment after instruction execution) – 223(increment before execution) => i = -112 , j =223 } } class ClassTwo extends ClassOne { { j = i– + –j; => j = -112(decrement after execution) + 222(decrement before execution) => j = 110 && i gets decremented after execution => i = -112-1 = -113 } } Hence i = -113, j=110 at the end

its giving error: non-static variable j cannot be referenced from a static context System.out.println(“i: ” + i +”\n” + “j: ” + j);

my code : class ClassOne { static int i = 111;

{ i = i++ – ++j; } }

public class ClassTwo extends ClassOne { public static void main(String [] args) { System.out.println(“i: ” + i +”\n” + “j: ” + j); }

{ j = i– + –j; }

i also gt sm otpt

variable j must be static static int j=222; then error will be removed but output same as given value output:111 222 becoz your all of instance block is not exicuted. it will be exicute during the class object creation. if you write this statenment in main method so all of instance block will exicute. ClassTwo obj1=new ClassTwo();

print the value of i and j in main class then the output will be -113 110

yes the output is wrong in the answer.

yes,output is wrong. correct output is -112 for i 110 for j

For Q.38), output is right. Try it on any software like netbeans, or can use online compiler.

I am Confused, please correct me.

I believe, Question number 2 is wrong. Because A a = new B() and a.i should be = 20.

Hi pri, It points to the type of the reference it is referred to, not the type of the reference it is assigned.

In case of overriding of method, it is reverse and it is so called Runtime Method Dispatch

hello divya can you please elaborate?

for eg. what would be the output in the following?

lass Animal{

public void move(){ System.out.println(“Animals can move”); } }

class Dog extends Animal{

public void move(){ System.out.println(“Dogs can walk and run”); } }

public class TestDog{

public static void main(String args[]){ Animal a = new Animal(); // Animal reference and object Animal b = new Dog(); // Animal reference but Dog object

a.move();// runs the method in Animal class

b.move();//Runs the method in Dog class

For me, both seems the same. Please enlighten me on this !!!

Hello Ash, the example u gave was of Run-time polymorphism, when u give reference of subclass to parent class variable and are calling the subclass method by the reference variable of Parent class. Since it refers to the subclass object and subclass method overrides the Parent class method, subclass method is invoked at runtime.

and in question no. 2 he is trying to do the same but Method is overridden not the datamembers, so runtime polymorphism can’t be achieved by data members. Since you are accessing the datamember which is not overridden, hence it will access the datamember of Parent class always.

animals can move dogs can walk and run

Hi pri This is variable not method variable not comes under overriding so its work as a overloading

I got the same view on it

i also think so.

the answer is true b/c it is a rule in java when is being created then control goes through parent class if it exist

Variables cannot be overloaded bro…

in 28 question i value not declared but it becomes 1 how is it

i is initialized to 0 in Parent Class and Child Class can access it has default access specifier. Execution Flow: All static blocks are executed, since there are no constructor’s initializer blocks are not executed.

please explain the line number 6 of question 20 m = m++;

There is a solution my friend

M=1111 is initialized .

When compiler goes to the statement

M=m++; then the processing of code is Firstly m++ is a post increament value so it follows first use then change so without changing to1112 it assigns 1111 to M.

Thats y we r getting output 1111.

if you compile only m++ and not assigning this m++ to M then definitely u will get 1112.

hope it helps you.

Q 26) Can enay explain below b.a.i = 2121;

System.out.println(“——–“);

System.out.println(a.i);

System.out.println(b.i);

Output: ———- ——– 2121 1212

Yes, b’s reference to (A a) actually points to the ‘a’ that was instantiated with this statement A a = new A();. This statement B b = new B(a); Notice the ‘a’ as an argument to the constructor. b’s b.a actually points to ‘a’. So b.a.i changes a’s int i.

can u explain question no 5

can u plzz explain 20 question

are u say Q20# or total 1-20 questions?

class A { int i = 10; }

class B extends A { int i = 20; }

public class MainClass { public static void main(String[] args) { A a = new B();

System.out.println(a.i); } }

This calls the parent class variable. But

class A { int i = 10;

public void print() { System.out.println(“class A”); } }

class B extends A { int i = 20;

public void print() { System.out.println(“class B”); } }

public class MainClass { public static void main(String[] args) { A a = new B(); a.print();

It calls the child method. Its like same inheritance. Can anybody tell me how is this?

public void print() { System.out.println(“class A”); } }

public void print() { System.out.println(“class B”); } }

In this case method call is based on actual reference type.And here in this case you are passing the reference of parent class.Where as in another question your are orerriding the print method in its sub-class in that case method cal l is based on actual object passed to it.

why output is 10 instead of 20? class A { int i = 10; }

Its because when you override a variable it creates separate copy of the variable, one corresponds to superclass , the other one for subclass. So here, a is a superclass reference of the object of type B. So it’s referring to the A portion of the variable.

here the output is 10 instead of 20 because during time of overriding non static data member create their own distinct copy,

class A { String s = “Class A”; }

class B extends A { String s = “Class B”;

{ System.out.println(super.s); } }

class C extends B { String s = “Class C”;

public class MainClass { public static void main(String[] args) { C c = new C();

System.out.println(c.s); } } View Answer Answer : Class A Class B Class C according to me output is class C class b class a please explain why it’s reverse.

First of all, initialization block is been put inside constructor by compiler. Here default constructor is used by compiler. C c = new C(); –> here C() constructor is called & by default , compiler will call super constructor which is B(), but there is no constructor mentioned, it will call again default constructor for B class & as I said it will put initialization block inside constructor. So System.out.println(super.s); of class B will be executed first, (super.s) is “Class A”. After this System.out.println(super.s); of class C will be executed so “Class B” will be print Then System.out.println(c.s);–> “Class C”

class X { int m = 1111;

System.out.println(m); } }

class Y extends X { { System.out.println(methodOfY()); }

int methodOfY() { return m– + –m; } }

public class MainClass { public static void main(String[] args) { Y y = new Y(); } }

30) Constructors are also inherited to sub classes. True or false? Answer : false. Constructors, SIB and IIB are not inherited to sub classes. But, they are executed while instantiating a subclass.

but on question 28) the code is executing without instantiating the class, means SIB is executing and giving output. anyone plz explain me more on this.

SIBs are executed during class loading i.e., when a .class file is loaded but before even a class is instantiated(or not instantiated) during execution time. So in any program all the static blocks will be executed even if an instance is created or not.

Excellent stuff good for java people.

Question 10)

I thought super class constructor will be call automatically. why it is added super(10).

Can a class be extended by more than one classes? ans is NO question no 35 is wrong answer because multiple inheritance not support in java

class A { …… } class B extends A{ …….. } class C extends A{ …………. } The above code is what the question interprets, that means A can be a parent class for any number of classes. This is example for hierarchical Inheritance.

On the other hand multiple inheritance means a class extending more than one class at the same time i.e., For example: class A extends B,C which creates ambiguity.

class A{   void msg(){System.out.println(“Hello”);}   }   class B{   void msg(){System.out.println(“Welcome”);}   }   class C extends A,B{//suppose if it were        Public Static void main(String args[]){      C obj=new C();      obj.msg();//Now which msg() method would be invoked?   }   }  

O/p: Compile time error

The object is created for class C but msg() is not overridden. so compiler throws an error.

no , i think you misunderstand the question,question is “can we use base /parent/super class in more than one class its a hierarical inheritance |—-c2 |—-c3 c1—-> |—-c4 |—-c5

Can anybody explain me the qstn number 16….as well as qstn 20 output is why 2220 why not 2221……

class M { static { System.out.println(‘A’); }

{ System.out.println(‘B’); }

public M() { System.out.println(‘C’); } }

class N extends M { static { System.out.println(‘D’); }

{ System.out.println(‘E’); }

public N() { System.out.println(‘F’); } }

public class MainClass { public static void main(String[] args) { N n = new N(); } }

can anyone explain question no. 16?

Please Explain Q 18 ?

public N(int j)     {         super(j);           System.out.println(i);           this.i = j * 20;

When the above code starts executing as a per the Statement; N n = new N(26); At this point of time, super(j); will point the execution to

public M(int j)     {         System.out.println(i);           this.i = j * 10; }

And ‘i’ will be printed which is 51 at that time, then the instance variable ‘i’ will change since its value as per this.i = j * 10; where j is 26, which makes the value of i as 260.

So the o/p so far is 51

Now the execution is handed back to the constructor in the child class N constructor as shown below: public N(int j)     {         super(j);         System.out.println(i);         this.i = j * 20;} Now value of i at this instance(i.e., 260) is printed.

Next this.i = j * 20; is executed and the value of i now is 520.

which is printed when the print statement in the main() method is executed.

in a file the classes like class A and class B are inherited and they are public. And even the main Class also public, then in what name the file should be saved. import java.io.*; public class A { int i = 10; }

public class B extends A { int i = 20; }

Question 17 has compile time error because super class don’t have default constructor.

Can anyone explain the reason of question no-2

The object a is declared as type A but it will not be aware of the variable i in class B. if you try to change the declaration as B a = new B(); Then you will get 20.

Can anyone explain the following code in Q.No-26 System.out.println(b.a.i);

b.a.i = 2121;

Yes, b’s reference to (A a) actually points to the ‘a’ that was instantiated with this statement A a = new A();. This statement B b = new B(a); Notice the ‘a’ as an argument to the constructor. b’s b.a actually points to ‘a’. So b.a.i changes a’s int i.

is call by value, call by reference applicable here, or is it part of c++ only?

Hi Rahul, A a = new B(); this is called casting. This statement tells Child class (B) referencing to parent class (A), so parent class instance varible will be printed. If this code is replaced with B b = new B(); System.out.println(b.i); // you can see “20” output. here child class instance is referncing to child class variable.

To admin Answer of Q#2 is wrong .You should correct it. Its correct answer is 20

Answer 10 is correct, overriden is applied only method not on instance variable.

I also thinks it should be 20.

can anyone explain ques 26

Q10) can you please explain the flow of execution

please help explaining 20 detail

please explain q32

please modify the code for Question 1 to make it runnable

I have a query regarding question number 12. As you said “Compiler will not keep super() if you are writing this() as a first statement in your constructor.” Please refer blow code and output public class Test {

public static void main(String[] args) { Y y = new Y(10); } }

class X { X(){ System.out.println(“X class”); } }

class Y extends X { Y(){ System.out.println(“Y class”); }

Y(int i){ this(); System.out.println(“Y class : “+ i); } }

Actual Output : X class Y class Y class : 10

Expected output : Y class Y class : 10

So conclusion is “Compiler will always keep super() whether we are writing this() or not as a first statement in your constructor.” Please correct me if I did anything wrong.

Anyone explain question 28. How the value of i will become 1.

Thanks, brother. Nice Article, Great work…!?

class A { public A(){ System.out.println(” A”); } static { System.out.println(“THIRD”); } }

class B extends A {

public B(){ System.out.println(“B”); } static { System.out.println(“SECOND”); } }

class C extends B { static { System.out.println(“FIRST”); }

public C(){ System.out.println(“C”); } }

public class MainClass { public static void main(String[] args) { A c = new C(); } }

Q no 9: Why output is Class Y and why not it is : Class X Class Y

Please explain Q20.

Q 21 class A { static String s = “AAA”;

static { s = s + “BBB”; }

{ s = “AAABBB”; } }

class B extends A { static { s = s + “BBBAAA”; }

{ System.out.println(s); } }

public class MainClass { public static void main(String[] args) { B b = new B(); }

how is answer AAABBB . shouldn’t be AAABBBBBBAAA .

When the Object is created B b = new B() ; it calls the default constructor in B which in turns calls the default constructor of A .. where s = AAA , static function of A is executed which makes s as AAABBB then IIB is executed which makes s = AAABBB, then control goes back to Class B where SIB is executed where s = s + “BBBAAA” which makes s as AAABBBBBBAAA and then IIB is executed which prints AAABBBBBBAAA ? Isn’t it correct . Please explain .

Q 21 ) first static methods are executed then non-static so s will get “AAABBBBBBAAA” and then s = “AAABBB” will and then print statement.

for Q20 output is as follows: 1112 2222

you are not taking into consideration the decrement and assignment rules for “–“:

i = m–; // the value of m is decreased after m is assigned to i, so “i” doesn’t change: i = 1111 and m=1110 j= –m; // the value of m is decreased before m is assigned to j, so m = 1110 – 1 = 1109 and then the result will be assigned to j, j = 1109 z = i + j; // thus z = 1111 + 1109 = 2220

Could anyone please explain the execution flow of the program given in Q16?

it’s a nice code

plz explain Question 26 I don’t understand what is b.a.i

Answer of Q31 is 0

Please explain question. 16 I didn’t understand the order of execution.

public class MainClass { public static void main(String[] args) { N n = new N(); } } //output : A D B C E F

==> We know that static block will be execute before the main ( So A & D will be printed at the top ) ==> Now the child class created an object for its own class and its constructor get invoked A child class constructor has super class as default so parent class constructor invoked and prints B & C, later child class constructors get printed E & F

Hi Can i have an explanation for number 5 , my answer was Class A only and yet also B and C are printed

class A { { System.out.println(1); } }

class B extends A { { System.out.println(2); } }

class C extends B { { System.out.println(3); } }

public class MainClass { public static void main(String[] args) { C c = new C(); } }

Can someone explain why its printing 1 2 3?

the order of excution in java is static block instance block constructor and any function that is called by an object instance block example { //some code } above block is called instance block

after C class object declaration there is call to its base class that is B and B is also inherited that is derived class if A so class A is called and the first thing is be executed is static block but there is no static block so instance block is executed of class A, B, C respectively in same order as 1 2 3

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The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available. See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases. See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.

Questions and Exercises: Inheritance

1. Consider the following two classes:

a. Which method overrides a method in the superclass? b. Which method hides a method in the superclass? c. What do the other methods do? 2. Consider the Card , Deck , and DisplayDeck classes you wrote in Questions and Exercises: Classes . What Object methods should each of these classes override?

1. Write the implementations for the methods that you answered in question 2.

Check your answers.

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  • Object Oriented Programming

Java Inheritance I

Using inheritance , one class can acquire the properties of others. Consider the following Animal class:

This class has only one method, walk . Next, we want to create a Bird class that also has a fly method. We do this using extends keyword:

Finally, we can create a Bird object that can both fly and walk .

The above code will print:

This means that a Bird object has all the properties that an Animal object has, as well as some additional unique properties.

The code above is provided for you in your editor. You must add a sing method to the Bird class, then modify the main method accordingly so that the code prints the following lines:

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Java Inheritance Tutorial: explained with examples

Java Inheritance Tutorial

Practice Problems on Inheritance in Java

Enhance your inheritance skills with these java practice problems.

Practice Problems on Inheritance in Java

Welcome to the article on “Practice Problems on Inheritance in Java”. Inheritance is a powerful concept in object-oriented programming, and it is important to understand its various aspects and applications. If you want to learn more about inheritance, please refer to our previous article titled “ Inheritance in Java “ . Additionally, if you are interested in learning about the different types of inheritance in Java, please refer to our article on “ Types of Inheritance in Java “ . In this article, we will cover a range of practice problems on inheritance in Java, which will help you solidify your understanding and skills in this area.

Practice Problem on Single Inheritance

Practice problem on multilevel inheritance, practice problem on hierarchical inheritance.

In conclusion, this article presented several practical problems on inheritance in Java, covering various concepts such as single inheritance, hierarchical inheritance, and more. By practicing these problems, you can improve your understanding of inheritance and become better at writing efficient and effective code using inheritance. We hope that these problems will be useful for you in your programming journey. If you want to learn more about inheritance or related concepts, refer to our previous articles such as “ Inheritance in Java ” or “ Types of Inheritance in Java “

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Mahesh Verma

I have been working for 10 years in software developing field. I have designed and developed applications using C#, SQL Server, Web API, AngularJS, Angular, React, Python etc. I love to do work with Python, Machine Learning and to learn all the new technologies also with the expertise to grasp new concepts quickly and utilize the same in a productive manner.

Exploring Types of Inheritance in Java

Practice problems on abstract class in java, you may also like, creating an analog clock with javascript, what can machine learning be used for, how does machine learning work, predict sales based on advertisement spending, php interview questions and answers – part 1, how to install xampp, dataframe practice questions with solutions (part-4 attributes and..., what is php and why it is used, practice questions on linear regression – predict score..., practice problems on linear regression in machine learning, leave a comment cancel reply.

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Problems With Inheritance in Java

Having trouble with proper subclass inheritance in java click here to figure out how to avoid broken code..

Yogen Rai user avatar

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Inheritance is one of the fundamental principles in an object-oriented paradigm, bringing a lot of values in software design and implementation. However, there are situations where even the correct use of inheritance breaks the implementations. This post is about looking at them closely with examples.

Fragility of Inheritance

The improper design of the parent class can leads subclasses of a superclass to use the superclass in unexpected ways. This often leads to broken code, even when the IS-A criterion is met. This architectural problem is known as the  fragile base class problem in object-oriented programming systems.

The obvious reason for this problem is that the developer of a base class has no idea of the subclass design. When they modify the base class, the subclass implementation could potentially break.

For example, the following program shows how seemingly an inheriting subclass can malfunction by returning the wrong value.

Now, the following shows how to the test to ensure that the inheritance works fine. 

Obviously, if I create the instance of  Square    and call a method  calculateArea , it will give the correct value. But, if I set any of dimension of the  square,  since the square is a rectangle, it gives the unexpected value for the area and the second assertion fails as below:

Is There Any Solution?

There is no straightforward solution to this problem because this is all about following the best practices while designing architecture. According to  Joshua Bloch , in his book  Effective Java , programmers should " design and document for inheritance or else prohibit it ."

If there is a breakable superclass, it is better to prohibit inheritance by labeling a declaration of a class or method, respectively, with the keyword " final. " And, if you are allowing your class to be extended, it is best to only use one way to populate fields.

Here, use either  constructors    or  setters    but not both.

So, if I remove the setters from the parent class as below:

Then, the child classes can't misuse the setter avoiding fragility issue as:

Inheritance Violates Encapsulation

Sometimes, your private data gets modified and violates encapsulation. This will happen if you are extending features from an undocumented parent class — even though the IS-A criterion is met.

For example, let us suppose A overrides all methods in B by first validating input arguments in each method (for security reasons). If a new method is added to B and A   and is not updated, the new method introduces a security hole.

For example, I have created new HashSet implementation to count the numbers of elements added to it as:

Everything looks good. So, it is time to test this extension!

The test fails with a failure in the last assertion as below:

The cause of the problem is that in the implementation of   HashSet, addAll    calls the  add    method. Therefore, we are incrementing  addCount    too many times in calls to   addAll.  

How to Fix This Issue?

The principle is the same as in an earlier fix: " Design and document for inheritance or else prohibit it."  The proper documentation while designing features would reduce the chances of issues like this. 

Fix specific to this issue is not to increment   addCount    in   addAll    operations, since the value is getting updated in  add    operation, which gets called from   addAll     as:

So, this is it! Until next time, happy learning!

As usual, all the source code presented in the above examples is available on GitHub .

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Java, Java, Java: Object-Oriented Problem Solving, 2022E

Ralph Morelli, Ralph Walde, Beryl Hoffman

Section 8.9 Inheritance Exercises

  • A method that lacks a body is an __________ method.
  • An __________ is like a class except that it contains only instance methods, no instance variables.
  • Two ways for a class to inherit something in Java is to __________ a class and __________ an interface.
  • Instance variables and instance methods that are declared __________ or __________ are inherited by the subclasses.
  • An object can refer to itself by using the __________ keyword.
  • If a GUI class intends to handle ActionEvent s, it must implement the __________ interface.
  • A __________ method is one that does different things depending upon the object that invokes it.
  • Class and interface.
  • Stub method and abstract method.
  • Extending a class and instantiating an object.
  • Defining a method and implementing a method.
  • A protected method and a public method.
  • A protected method and a private method.
  • Draw a hierarchy to represent the following situation. There are lots of languages in the world. English, French, Chinese, and Korean are examples of natural languages. Java, C, and C++ are examples of formal languages. French and Italian are considered romance languages, while Greek and Latin are considered classical languages.
  • Look up the documentation for the JButton class on Sun’s Web site: http://java.sun.com/j2se/1.5.0/docs/api/ . List the names of all the methods that would be inherited by the ToggleButton subclass that we defined in this chapter.
  • Design and write a toString() method for the ToggleButton class defined in this chapter. The toString() method should return the ToggleButton ’s current label.
  • Design a class hierarchy rooted in the class Employee that includes subclasses for HourlyEmployee and SalaryEmployee . The attributes shared in common by these classes include the name, and job title of the employee, plus the accessor and mutator methods needed by those attributes. The salaried employees need an attribute for weekly salary, and the corresponding methods for accessing and changing this variable. The hourly employees should have a pay rate and an hours worked variable. There should be an abstract method called calculateWeeklyPay() , defined abstractly in the superclass and implemented in the subclasses. The salaried worker’s pay is just the weekly salary. Pay for an hourly employee is simply hours worked times pay rate.
  • Design and write a subclass of JTextField called IntegerField that is used for inputting integers but behaves in all other respects like a JTextField . Give the subclass a public method called getInteger() .
  • Implement a method that uses the following variation of the Caesar cipher. The method should take two parameters, a String and an int N . The result should be a String in which the first letter is shifted by N , the second by \(N+1\text{,}\) the third by \(N+2\text{,}\) and so on. For example, given the string “Hello,” and an initial shift of 1, your method should return “Igopt.” Write a method that converts its String parameter so that letters are written in blocks five characters long.
  • Design and implement an GUI that lets the user type a document into a TextArea and then provides the following analysis of the document: the number of words in the document, the number of characters in the document, and the percentage of words that have more than six letters.
  • Design and implement a Cipher subclass to implement the following substitution cipher: Each letter in the alphabet is replaced with a letter from the opposite end of the alphabet: a is replaced with z , b with y , and so forth.
  • One way to design a substitution alphabet for a cipher is to use a keyword to construct the alphabet. For example, suppose the keyword is “zebra.” You place the keyword at the beginning of the alphabet, and then fill out the other 21 slots with remaining letters, giving the following alphabet: Cipher alphabet: zebracdfghijklmnopqstuvwxy Plain alphabet: abcdefghijklmnopqrstuvwxyz Design and implement an Alphabet class for constructing these kinds of substitution alphabets. It should have a single public method that takes a keyword String as an argument and returns an alphabet string. Note that an alphabet cannot contain duplicate letters, so repeated letters in a keyword like “xylophone” would have to be removed.
  • Design and write a Cipher subclass for a substitution cipher that uses an alphabet from the Alphabet class created in the previous exercise. Challenge: Find a partner and concoct your own encryption scheme. Then work separately with one partner writing encode() and the other writing decode() . Test to see that a message can be encoded and then decoded to yield the original message.
  • Design a TwoPlayerGame subclass called MultiplicationGame . The rules of this game are that the game generates a random multiplication problem using numbers between 1 and 10, and the players, taking turns, try to provide the answer to the problem. The game ends when a wrong answer is given. The winner is the player who did not give a wrong answer.
  • Design a class called MultiplicationPlayer that plays the multiplication game described in the previous exercise. This class should implement the IPlayer interface.
  • Design a TwoPlayerGame subclass called RockPaperScissors . The rules of this game are that each player, at the same time, picks either a rock, a paper, or a scissors. For each round, the rock beats the scissors, the scissors beats the paper, and the paper beats the rock. Ties are allowed. The game is won in a best out of three fashion when one of the players wins two rounds.
  • Design a class called RockPaperScissorsPlayer that plays the the game described in the previous exercise. This class should implement the IPlayer interface.
  • Given the classes with the following headers public class Animal ... public class DomesticAnimal extends Animal ... public class FarmAnimal extends DomesticAnimal... public class HousePet extends DomesticAnimal... public class Cow extends FarmAnimal ... public class Goat extends FarmAnimal ... public class DairyCow extends Cow ... draw a UML class diagram representing the hierarchy created by these declarations.
  • Given the preceding hierarchy of classes, which of the following are legal assignment statements? DairyCow dc = new FarmAnimal(); FarmAnimal fa = new Goat(); Cow c1 = new DomesticAnimal(); Cow c2 = new DairyCow(); DomesticAnimal dom = new HousePet();
  • The JFrame that follows contains a semantic error in its SomeFrame() constructor. The error will cause the actionPerformed() method never to display “Clicked” even though the user clicks the button in the JFrame. Why? ( Hint : Think scope!) public class SomeFrame extends JFrame implements ActionListener { // Declare instance variables private JButton button; public JFrame() { // Instantiate the instance variable JButton button = new JButton("Click me"); add(button); button.addActionListener(this); } // init() public void actionPerformed(ActionEvent e) { if (e.getSource() == button) System.out.println("Clicked"); } // actionPerformed() } // SomeFrame
  • What would be output by the following program? public class SomeFrame2 extends JFrame { // Declare instance variables private JButton button; private JTextField field; public SomeFrame() { // Instantiate instance variables button = new JButton("Click me"); add(button); field = new JTextField("Field me"); add(field); System.out.println(field.getText() + button.getText()); } // init() public static void main(String[] args) { SomeFrame2 frame = new SomeFrame2(); frame.setSize(400,400); frame.setVisible(true); } } // SomeFrame2
  • Design and implement a GUI that has a JButton , a JTextField , and a JLabel and then uses the toString() method to display each object’s string representation.
  • The JButton class inherits a setText(String s) from its AbstractButton() superclass. Using that method, design and implement a GUI that has a single button labeled initially, “The Doctor is out.” Each time the button is clicked, it should toggle its label to, “The Doctor is in” and vice versa.

practice problems on inheritance in java

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    Inheritance is an important pillar of OOP(Object Oriented Programming). ... Problem Submissions Comments. Java Inheritance. School Accuracy: 72.83% Submissions: 18K+ Points: 0. Internship Alert! Become an SDE Intern by topping this monthly leaderboard! Inheritance is an important pillar of OOP(Object Oriented Programming). It is the mechanism ...

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    i Line: 12 Col: 1 Submit Code Run Code Upload Code as File Author Shafaet Using Inheritance one class can acquire the properties of others. This problem gives you an introduction to Java Inheritance.

  9. Inheritance in Java

    Child classes can directly use the parent class code. Method Overriding is achievable only through Inheritance. It is one of the ways by which Java achieves Run Time Polymorphism. The concept of abstract where we do not have to provide all details is achieved through inheritance. only shows the functionality to the user.

  10. Guide to Inheritance in Java

    1. Overview One of the core principles of Object-Oriented Programming - inheritance - enables us to reuse existing code or extend an existing type. Simply put, in Java, a class can inherit another class and multiple interfaces, while an interface can inherit other interfaces.

  11. Inheritance in Java

    Question 1 Output of following Java Program? class Base { public void show () { System.out.println ("Base::show () called"); } } class Derived extends Base { public void show () { System.out.println ("Derived::show () called"); } } public class Main { public static void main (String [] args) { Base b = new Derived ();; b.show (); } }

  12. Java Inheritance Tutorial: explained with examples

    Inheritance is the process of building a new class based on the features of another existing class. It is used heavily in Java, Python, and other object-oriented languages to increase code reusability and simplify program logic into categorical and hierarchical relationships. However, each language has its own unique way of implementing ...

  13. Practice Problems on Inheritance in Java

    Practice Problems on Inheritance in Java Enhance Your Inheritance Skills with these Java Practice Problems written by Mahesh Verma May 8, 2023 Welcome to the article on "Practice Problems on Inheritance in Java". Inheritance is a powerful concept in object-oriented programming, and it is important to understand its various aspects and applications.

  14. Java Tutorial: Exercise & Practice Questions on Inheritance

    Chapter 10 Inheritance: Practice Set - In this video we will solve some of the important practice questions on inheritance and object oriented programming in Java This playlist is a part of...

  15. Problems With Inheritance in Java

    java.lang.AssertionError: New number of attempted adds so far Expected :6 Actual :9 Inheritance The cause of the problem is that in the implementation of HashSet, addAll calls the add method.

  16. PDF Chapter 8: Inheritance Lab Exercises

    Lab Exercises Exploring Inheritance A Sorted Integer List Test Questions Overriding the equals Method Extending Adapter Classes Rebound Revisited Count Down Exploring Inheritance File Dog.java contains a declaration for a Dog class. Save this file to your directory and study it—notice what instance variables and methods are provided.

  17. PDF Practice Problems: Inheritance & Polymorphism

    Practice Problems: Inheritance & Polymorphism public class Foo { public void method1() { System.out.println("foo 1"); } public void method2() { System.out.println("foo 2"); } public String toString() { return "foo"; } } public class Bar extends Foo { public void method2() { System.out.println("bar 2"); } }

  18. Inheritance in Java

    Inheritance in Java is a mechanism in which one object acquires all the properties and behaviors of a parent object. It is an important part of OOPs (Object Oriented programming system).. The idea behind inheritance in Java is that you can create new classes that are built upon existing classes. When you inherit from an existing class, you can reuse methods and fields of the parent class.

  19. Inheritance Exercises

    Inheritance Exercises. 🔗. (Note: For programming exercises, first draw a UML class diagram describing all classes and their inheritance relationships and/or associations.) Fill in the blanks in each of the following sentences: A method that lacks a body is an __________ method. An __________ is like a class except that it contains only ...

  20. Java programming Exercises, Practice, Solution

    Here you have the opportunity to practice the Java programming language concepts by solving the exercises starting from basic to more complex exercises. A sample solution is provided for each exercise. It is recommended to do these exercises by yourself first before checking the solution. Hope, these exercises help you to improve your Java ...

  21. Java Polymorphism: Exercises, Practice and Solutions

    Java Polymorphism Programming: Exercises, Practice, Solution - Enhance your understanding of Java polymorphism through hands-on exercises and solutions. Learn to create subclasses, override methods, and implement polymorphic behavior in Java programs. Explore examples with animals, vehicles, shapes, employees, and sports.

  22. Types of Inheritance Practice Problem in Advance Java

    Types of Inheritance. There are different types of Inheritance supported in Java. Single inheritance is the most basic type of inheritance. It occurs when a subclass inherits from only one superclass. Like in the example we saw previously where the Dog class now extends the Animal class. The next type is Multilevel inheritance.

  23. What is Inheritance Practice Problem in Advance Java

    What is Inheritance. In Java, inheritance allows you to create a new class that is a modified version of an existing class. The new class is called the subclass, and the existing class is called the superclass. The subclass inherits all the methods and variables of the superclass, and can also add its own methods and variables.