Code segment concerning polymorphism. Why does the following result in a compilation error?

which of the following classes cannot be extended?
the set of all instances of a subclass is a subset of the instances of its superclass.
you can always successfully cast a subclass to a superclass.
polymorphism means that data fields should be declared private
which of the following class definitions defines a legal abstract class?
you can create an arraylist using
given two reference variables t1 and t2, if t1.equals(t2) is true, t1 == t2
dynamic binding can apply to static methods

Why does the following code result in a compilation error? Since it is a GeeksforGeeks object, shouldn't it use the getValue() method found in class GeeksforGeeks. I added a getValue() method to the base class and the code compiled. What is the reasoning for this?

class GFG 
{ 
    protected void getData() 
    { 
        System.out.println("Inside GFG"); 
    } 
} 

class GeeksforGeeks extends GFG 
{ 
    protected void getData() 
    { 
        System.out.println("Inside GeeksforGeeks"); 
    } 

    protected void getValue() 
    { 
        System.out.println("GeeksforGeeks"); 
    } 
} 

public class Test 
{ 
    public static void main(String[] args) 
    { 
        GFG obj = new GeeksforGeeks(); 
        obj.getValue(); 
    } 
}

It's because the Reference Variable of obj is of Type GFG and that class does not have a getValue() Method. If you change the Reference Variable to GeeksForGeeks it would work.

Introduction to Java Programming, B. The program has a compile error because the default constructor of A invokes the default constructor of B, but B does not D. The program compiles, but it has a runtime error due to the conflict on the method name print. 11.16 Given the following code, find the compile error. This feature is known as polymorphism. In computer terminology, polymorphic code is code that uses a polymorphic engine to mutate while keeping the original algorithm intact. That is, the code changes itself each time it runs, but the function of the code (its semantics) will not change at all. For example, 1+3 and 6-2 both achieve the same result while using different values and

The problem here is that the getValue() method only exists in the GeeksForGeeks subclass, but not in the parent class CFG. And in your code, you define obj to be of the parent class type.

One fix here would be to just give CFG a getValue() method:

class GFG {
    protected void getData() {
        System.out.println("Inside GFG");
    }

    protected void getValue() {
        // do something
    }
}

By adding any implementation for getValue() to the CFG class, you will complete the inheritance chain, and Java should then call the overloaded version in the GeeksForGeeks subclass.

OOP Concepts for Beginners: What is Polymorphism, Polymorphism is one of the core concepts in OOP languages. Learn about the concept, different types, and classes along with code examples. In the following code snippet, I call the method only with a At compile time, the Java compiler binds this method call to the Retrace Logging and Error Tips� Polymorphism allows a programmer to manipulate objects that share a set of tasks, even though the tasks are executed in different ways. Polymorphism allows a programmer to use a subclass object in place of a superclass object. Polymorphism allows a subclass to override a superclass method by providing a completely new implementation.

You are declaring obj as a GFG object. GFG does not contain the getValue() method.

It is important to understand that parent objects do not inherit from their children. So, while GeeksForGeeks is a GFG, a GFG is not a GeeksForGeeks (just like a Buick is a Car, but not every Car is a Buick).

Update your line to GeeksForGeeks obj = new GeeksForGeeks(); or move the getValue() method to your GFG class and you'll be right as rain.


You should think about your design a bit. Will every class that extends GFG need to have a getValue() method? If so, and they'll all do the same thing, that method belongs in the GFG class.

Suppose, however, that you want each child of GFG to run its own code when getValue() is called. Then you would still want getValue() declared in GFG, but you'd override it in your GeeksForGeeks class:

@Override
public void getValue(){
    // Code here
}

This is an overly-simplified explanation of inheritance, but should lead you in the right direction as there's much to learn on the subject.

Side Note: Your getValue() method does not actually return anything; this would be a confusing implementation; what is the caller "getting" from the method?

AP Computer Science chapter 9 Flashcards, Will the following code fragment compile? Will it run? If not, what error is reported ? Object obj = "Who was the inventor of Java?"; Question q =� When the above code is compiled and executed, it produces the following result − Printing int: 5 Printing float: 500.263 Printing string: Hello C++ Dynamic Polymorphism. C# allows you to create abstract classes that are used to provide partial class implementation of an interface. Implementation is completed when a derived class inherits from it.

[PDF] An Introduction to Polymorphism in Java, among) methods depending on either the method signature (after compile) or the object knows after the compile to the byte code which of the add methods it will execute. That is Consider the following example. would result in a “type incompatibility” compile error message unless a type cast were made on the actual. Dynamic (run time) polymorphism is the polymorphism existed at run-time. Here, Java compiler does not understand which method is called at compilation time. Only JVM decides which method is called at run-time. Method overloading and method overriding using instance methods are the examples for dynamic polymorphism.

[PDF] Final Exam, Version 1 Solutions, (6 pts) Rewrite the following code segment using if-else statements. (2 pts) What command do you type to compile class Echo (from the command returns true when the team has a good record and print out the result. The first four questions reference three error-free Java files, which are printed on the� Polymorphism is the ability of a message to be processed in more than one way. A different member function can be invoked at different instances depending on the object which is invoking the function. Function Overloading provides the concept of static or compile time polymorphism. During compilation phase, it is […]

OOP Inheritance & Polymorphism - Java Programming Tutorial, With inheritance, you derive a new class based on an existing class, with The Book class (as shown in the class diagram) contains the following members: The source code is HERE. If @Override is used, the compiler will signal an error. As a result, we can substitute a subclass instance when a superclass instance� The word polymorphism means having many forms. Typically, polymorphism occurs when there is a hierarchy of classes and they are related by inheritance. C++ polymorphism means that a call to a member function will cause a different function to be executed depending on the type of object that invokes the function.

Comments
  • You declare the object as a GFG, which does not contain the getValue() method. Parents do not inherit from their children.
  • It states cannot resolve method getValue();