Core Java - Interview Questions and Answers

71) Difference between method Overloading and Overriding.

Method Overloading	Method Overriding
1) Method overloading increases the readability of the program.	Method overriding provides the specific implementation of the method that is already provided by its superclass.
2) Method overloading occurs within the class.	Method overriding occurs in two classes that have IS-A relationship between them.
3) In this case, the parameters must be different.	In this case, the parameters must be the same.

72) Can we override the private methods?

No, we cannot override the private methods because the scope of private methods is limited to the class and we cannot access them outside of the class.

73) Can we change the scope of the overridden method in the subclass?

Yes, we can change the scope of the overridden method in the subclass. However, we must notice that we cannot decrease the accessibility of the method. The following point must be taken care of while changing the accessibility of the method.

The private can be changed to protected, public, or default.
The protected can be changed to public or default.
The default can be changed to public.
The public will always remain public.

74) Can we modify the throws clause of the superclass method while overriding it in the subclass?

Yes, we can modify the throws clause of the superclass method while overriding it in the subclass. However, there are some rules which are to be followed while overriding in case of exception handling.

If the superclass method does not declare an exception, subclass overridden method cannot declare the checked exception, but it can declare the unchecked exception.
If the superclass method declares an exception, subclass overridden method can declare same, subclass exception or no exception but cannot declare parent exception.

75) What is covariant return type?

Now, since java5, it is possible to override any method by changing the return type if the return type of the subclass overriding method is subclass type. It is known as covariant return type. The covariant return type specifies that the return type may vary in the same direction as the subclass.

 class A{ A get(){return this;} }  class B1 extends A{ B1 get(){return this;} void message(){System.out.println("welcome to covariant return type");}  public static void main(String args[]){ new B1().get().message(); } } 

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 Output: welcome to covariant return type

76) What is the final variable?

In Java, the final variable is used to restrict the user from updating it. If we initialize the final variable, we can't change its value. In other words, we can say that the final variable once assigned to a value, can never be changed after that. The final variable which is not assigned to any value can only be assigned through the class constructor.

  class Bike9{   final int speedlimit=90;//final variable   void run(){    speedlimit=400;   }   public static void main(String args[]){   Bike9 obj=new  Bike9();   obj.run();   }  }//end of class  

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 Output:Compile Time Error

77) What is the final method?

If we change any method to a final method, we can't override it.

 class Bike{   final void run(){System.out.println("running");} }     class Honda extends Bike{    void run(){System.out.println("running safely with 100kmph");}        public static void main(String args[]){    Honda honda= new Honda();    honda.run();    } } 

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 Output:Compile Time Error

78) What is the final class?

If we make any class final, we can't inherit it into any of the subclasses.

  final class Bike{}    class Honda1 extends Bike{    void run(){System.out.println("running safely with 100kmph");}        public static void main(String args[]){    Honda1 honda= new Honda1();    honda.run();    }  } 

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 Output:Compile Time Error

79) What is the final blank variable?

A final variable, not initialized at the time of declaration, is known as the final blank variable. We can't initialize the final blank variable directly. Instead, we have to initialize it by using the class constructor. It is useful in the case when the user has some data which must not be changed by others, for example, PAN Number. Consider the following example:

80) Can we initialize the final blank variable?

Yes, if it is not static, we can initialize it in the constructor. If it is static blank final variable, it can be initialized only in the static block.

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