The different ways to overload a method are given as follows:
By changing the number of parameters used
By changing the order of parameters
By using different data types for the parameters
50. Differentiate between an abstract class and an interface.
A class can extend only one abstract class
The members of abstract class can be private as well as protected.
Abstract classes should have subclasses
Any class can extend an abstract class.
Methods in abstract class can be abstract as well as concrete.
There can be a constructor for abstract class.
The class extending the abstract class may or may not implement any of its method.
An abstract class can implement methods.
A class can implement several interfaces
An interface can only have public members.
Interfaces must have implementations by classes
Only an interface can extend another interface.
All methods in an interface should be abstract
Interface does not have constructor.
All methods of interface need to be implemented by a class implementing that interface.
Interfaces cannot contain body of any of its method.
51. What are queues and stacks?
Stacks refer to a list in which all items are accessed and processed on the Last-In-First-Out (LIFO) basis. In a stack, elements are inserted (push operation) and deleted (pop operation) from the same end called top.
Queues refer to a list in which insertion and deletion of an item is done on the First-In-First-Out (FIFO) basis. The items in a queue are inserted from the one end, called the rear end, and are deleted from the other end, called the front end of the queue.
52. Define an event.
Whenever an action takes place in a class, that class provides a notification to other classes or objects that are assigned to perform particular tasks. These notifications are called events. For example, when a button is clicked, the class generates an event called Click. An event can be declared with the help of the event keyword.
53. What are structures?
Structure is a heterogeneous collection of elements referenced by the same name. A structure is declared using the struct keyword. The following is an example that creates a structure to store an employee’s information:
fixed int empID;
fixed char name;
fixed char addr;
fixed char dept;
fixed char desig;
The preceding example defines a structure emp and the members of this structure specify the information of an employee.
54. When do you really need to create an abstract class?
We define abstract classes when we define a template that needs to be followed by all the derived classes.