Question

JAVA QUESTIONS:

1. What are the differences between constructors and other methods?

2. What is a NullPointerException and how should it be handled?

3. What must a class do to implement an interface and what must a class do to extend another class?

Answer 1

Ques 1.

• A constructor is a special type of method which is called automatically when an object of a class is created. But a normal method has to be called explicitly using the object.
• Also, the function can be public, private and protected, but the constructor is always public.
• Also, the name of the constructor is the same as he name of the class. But method has a different name than the class name.

Ques 2. A NullPointerException is a type of exception which is thrown when an object is used, but it has null value. So, we are trying to access a null value. So, NullPointerException is thrown.

We can handle the exception using try-catch block to run a code in case exception occurs.

// to check for exception

try{

// code which can throw NullPointerException

}

catch( NullPointerException e ){

  // code which runs when an exception occurs

}

Ques 3. In order to omplement an interface, we will use the implements keyword after the class name.

e.g:

class class_name implements interface_name {

}

Also, we need to override each function present in the interface inside class. Otherwise it will show error.

For inheriting the class, we use the extends keyword and then the name of the class to be inherited. e.g:

class class_name extends class_to_be_inherited_name {

}