Self Testing Questions on Java

What is the difference between exception and error?

The exception class defines mild error conditions that your program encounters. Exceptions can occur when trying to open the file, which does not exist, the network connection is disrupted, operands being manipulated are out of prescribed ranges, the class file you are interested in loading is missing. The error class defines serious error conditions that you should not attempt to recover from. In most cases it is advisable to let the program terminate when such an error is encountered.

What is the difference between process and thread?

Process is a program in execution whereas thread is a separate path of execution in a program.

What is multithreading and what are the methods for inter-thread communication and what is the class in which these methods are defined?

Multithreading is the mechanism in which more than one thread run independent of each other within the process. wait (), notify () and notifyAll() methods can be used for inter-thread communication and these methods are in Object class. wait() : When a thread executes a call to wait() method, it surrenders the object lock and enters into a waiting state. notify() or notifyAll() : To remove a thread from the waiting state, some other thread must make a call to notify() or notifyAll() method on the same object.

What is synchronization?

Synchronization is the mechanism that ensures that only one thread is accessed the resources at a time.

Are there any global variables in Java, which can be accessed by other part of your program?

No, it is not the main method in which you define variables. Global variables is not possible because concept of encapsulation is eliminated here.

What is an applet?

Applet is a dynamic and interactive program that runs inside a web page displayed by a java capable browser.

What is the difference between applications and applets?

a) Application must be run on local machine whereas applet needs no explicit installation on local machine. 

b) Application must be run explicitly within a java-compatible virtual machine whereas applet loads and runs itself automatically in a java-enabled browser. 

c) Application starts execution with its main method whereas applet starts execution with its init method. 

d) Application can run with or without graphical user interface whereas applet must run within a graphical user interface.

What is a layout manager and what are different types of layout managers available in java AWT?

A layout manager is an object that is used to organize components in a container. The different layouts are available are FlowLayout, BorderLayout, CardLayout, GridLayout and GridBagLayout.

How are the elements of different layouts organized?

FlowLayout: The elements of a FlowLayout are organized in a top to bottom, left to right fashion. BorderLayout: The elements of a BorderLayout are organized at the borders (North, South, East and West) and the center of a container. CardLayout: The elements of a CardLayout are stacked, on top of the other, like a deck of cards. GridLayout: The elements of a GridLayout are of equal size and are laid out using the square of a grid. 

GridBagLayout: The elements of a GridBagLayout are organized according to a grid. However, the elements are of different size and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.

What are wrapper classes?

Wrapper classes are classes that allow primitive types to be accessed as objects.

What are Vector, Hashtable, LinkedList and Enumeration?

Vector : The Vector class provides the capability to implement a growable array of objects. Hashtable : The Hashtable class implements a Hashtable data structure. A Hashtable indexes and stores objects in a dictionary using hash codes as the objectís keys. Hash codes are integer values that identify objects.

LinkedList: Removing or inserting elements in the middle of an array can be done using LinkedList. A LinkedList stores each object in a separate link whereas an array stores object references in consecutive locations.

Enumeration: An object that implements the Enumeration interface generates a series of elements, one at a time. It has two methods, namely hasMoreElements() and nextElement(). HasMoreElemnts() tests if this enumeration has more elements and nextElement method returns successive elements of the series.

What is an I/O filter?

An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.

What is JDBC?

JDBC is a set of Java API for executing SQL statements. This API consists of a set of classes and interfaces to enable programs to write pure Java Database applications.

What are drivers available?

a) JDBC-ODBC Bridge driver 

b) Native API Partly-Java driver 

c) JDBC-Net Pure Java driver 

d) Native-Protocol Pure Java driver.

What is the difference between JDBC and ODBC?

a) OBDC is for Microsoft and JDBC is for Java applications. 

b) ODBC canít be directly used with Java because it uses a C interface. 

c) ODBC makes use of pointers which have been removed totally from Java. 

d) ODBC mixes simple and advanced features together and has complex options for simple queries. But JDBC is designed to keep things simple while allowing advanced capabilities when required. 

e) ODBC requires manual installation of the ODBC driver manager and driver on all client machines. JDBC drivers are written in Java and JDBC code is automatically installable, secure, and portable on all platforms. 

f) JDBC API is a natural Java interface and is built on ODBC. JDBC retains some of the basic features of ODBC.

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