Java, JDBC, Servelts AND JSP FAQs Part I

What are Encapsulation, Inheritance and Polymorphism?

Encapsulation is the mechanism that binds together code and data it manipulates and keeps both safe from outside interference and misuse. Inheritance is the process by which one object acquires the properties of another object. Polymorphism is the feature that allows one interface to be used for general class actions.

What is OOPs?

Object oriented programming organizes a program around its data, i. e. , objects and a set of well defined interfaces to that data. An object-oriented program can be characterized as data controlling access to code.

What are Class, Constructor and Primitive data types?

Class is a template for multiple objects with similar features and it is a blue print for objects. It defines a type of object according to the data the object can hold and the operations the object can perform. Constructor is a special kind of method that determines how an object is initialized when created. Primitive data types are 8 types and they are: byte, short, int, long, float, double, boolean, char.

What is an Object and how do you allocate memory to it?

Object is an instance of a class and it is a software unit that combines a structured set of data with a set of operations for inspecting and manipulating that data. When an object is created using new operator, memory is allocated to it.

What is the difference between constructor and method?

Constructor will be automatically invoked when an object is created whereas method has to be called explicitly.

What is the use of bin and lib in JDK?

Bin contains all tools such as javac, appletviewer, awt tool, etc., whereas lib contains API and all packages.

What are different types of access modifiers?

public: Any thing declared as public can be accessed from anywhere. private: Any thing declared as private canít be seen outside of its class. protected: Any thing declared as protected can be accessed by classes in the same package and subclasses in the other packages. default modifier : Can be accessed only to classes in the same package.

What is final, finalize() and finally?

final : final keyword can be used for class, method and variables. A final class cannot be subclassed and it prevents other programmers from subclassing a secure class to invoke insecure methods. A final method canít be overridden. A final variable canít change from its initialized value. finalize() : finalize() method is used just before an object is destroyed and can be called just prior to garbage collection. finally : finally, a key word used in exception handling, creates a block of code that will be executed after a try/catch block has completed and before the code following the try/catch block. The finally block will execute whether or not an exception is thrown. For example, if a method opens a file upon exit, then you will not want the code that closes the file to be bypassed by the exception-handling mechanism. This finally keyword is designed to address this contingency.

What is UNICODE?

Unicode is used for internal representation of characters and strings and it uses 16 bits to represent each other.

What is Garbage Collection and how to call it explicitly?

When an object is no longer referred to by any variable, java automatically reclaims memory used by that object. This is known as garbage collection. System. gc() method may be used to call it explicitly.

What is difference between overloading and overriding?

a) In overloading, there is a relationship between methods available in the same class whereas in overriding, there is relationship between a superclass method and subclass method. 

b) Overloading does not block inheritance from the superclass whereas overriding blocks inheritance from the superclass. 

c) In overloading, separate methods share the same name whereas in overriding, subclass method replaces the superclass. 

d) Overloading must have different method signatures whereas overriding must have same signature.

What is the difference between superclass and subclass?

A super class is a class that is inherited whereas sub class is a class that does the inheriting.

What is a package?

A package is a collection of classes and interfaces that provides a high-level layer of access protection and name space management.

What is interface and its use?

Interface is similar to a class which may contain methodís signature only but not bodies and it is a formal set of method and constant declarations that must be defined by the class that implements it. Interfaces are useful for: 

a)Declaring methods that one or more classes are expected to implement 

b)Capturing similarities between unrelated classes without forcing a class relationship. 

c)Determining an objectís programming interface without revealing the actual body of the class.

What is the difference between Array and vector?

Array is a set of related data type and static whereas vector is a growable array of objects and dynamic.

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