What is Object class and java.lang ?

Object class is the superclass of all the classes and means that reference variable of type object can refer to an object of any other class. and also defines methods like finalise,wait.

java.lang contains all the basic language functions and is imported in all the programs implicitly.

What r packages and why ? how to execute a program in a package ?

Package is a set of classes, which can be accessed by themselves and cannot be accessed outside the package. and can be defined as package <pkg name>.

Package name and the directory name must be the same.

And the execution of programs in package is done by : java mypack.account

where mypack is directory name and account is program name.

What does a java source file can contain ?

specifying package name.

importing more than one package

specifying classes and there methods

………………

Why interface and what extends what ?

Interface is similar to abstract classes. this define only method declarations and definitions are specified in the classes which implements these interfaces.

and “ one interface multiple methods “ signifies the polymorphism concept.

Here an interface can extend another interface.

and a class implements more than one interface.

How Exception handling is done in Java ?

Is managed via 5 keywords :

try : statements that you want to monitor the exceptions contain in try block.

catch : the exception thrown by try is catched by this.

throw : to manually throw exception we go for this.

throws : Exception that is thrown out of a method must be specified by throws after the method declaration.

finally : this block is executed whether or not an exception is thrown. and also it is executed just before the method returns. and this is optional block.

What r checked and unchecked Exceptions ?

* Unchecked Exceptions are those which r not included in throws list and are derived from RuntimeException which are automatically available and are in java.lang.

* Checked Exceptions are those which cannot handle by itself.

What is Thread and multithread ? How is thread created ?

Thread is a small unit of dispatchable code. ie., a single program can perform more than one task simultaneously. This is a light weight process and is of low cost.

MultiThreading writes more efficient programs and make maximum use of CPU ie., it minimizes its idle time.

A Thread is created in two ways :

1) By implementing the runnable interface.

2) By extending the Thread class itself.

First way is used to update only run() method. ie we can use only run() method in this class.

Second way is used to define several methods overridden by derived class.

Generally we override only run() method so we go for runnable interface.

What are the various states and methods of thread ?

States : Running, Ready to run, Suspended, Resumed, blocked and terminated.

Methods : getName, getPriority, isAlive, join, run, sleep, start.

Thread priorities are MIN_PRIORITY, MAX_PRIORITY, NORM_PRIORITY.

What is interprocess synchronization ? ( also called Monitor, Semaphore )

Consider a small box namely MONITOR that can hold only one thread. Once a thread enters a monitor, all other threads must wait until that thread exits the monitor.

In this way, a monitor can be used to protect a shared asset from being manipulated by more than one thread at a time.

Once a thread is inside a synchronized method, no other thread can call any other synchronized method on the same object.

What is Stream ?

It is an Abstraction that either produces or consumes information.

Two types : Byte Stream and Character Stream.

Print Writer is to Print output in Real World Programs.

How to enter data in java ?

First specify :

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

then say br.read(), and this is put in do while loop to receive as many as we require.

Define Inline Functions ?

In ordinary functions, during the program execution, at any function call the controller jumps to the function definition, performs operation and returns the value, then comes back to the program.

whereas in Inline functions the controller copies the complete function definition into the program and performs operations.

What are the four components in URL ?

http:// www. yahoo .com : 8080 / index.html

http: — > is protocol

www. yahoo .com —à is IP address

8080 –à port number and is a pointer to memory location.

index.html –à file path to be loaded

What is a StringTokenizer ?

String Tokenizer provide parsing process in which it identifies the delimiters provided by the user , by default delimiters are spaces, tab, newline etc. and separates them from the tokens. Tokens are those which are separated by delimiters.

What are macros and Inline functions ? Which is best and Difference ?

Inline functions do Parameter passing, where as Macros do Text Substitution.

Its better to go for Inline functions than macros, else you may get different results.

How to Declare a pointer to function ?

int func_name(float) //ordinary declaration of function.

int (*func_name_ptr)(float) // Declaration of pointer.

Assigning the Address can be done as :

func_name_ptr = func_name. // Return type and Signatures must be Same.

Invoking a function pointer : int x = (*func_name_ptr)(values as specified);

What is a file ? What is a Directory ?

File : Describes the properties of file, like permissions, time, date, directory path, and to navigate subdirectory hierarchies.

Directory : Is a file that contains list of other files and directories .

What is Serialization ?

The process of writing the state of an object to a byte stream. and can restore these objects by using deserialization.

Is also need to implement RMI, which allows a java object of one machine to invoke java object of another machine.

ie., the object is passed as an argument by serializing it and the receiving machine deserializes it.

Interfaces include by java.lang ?

Java.lang is the package of all the classes.

And is automatically imported into all Java programs.

Intefaces : Cloneable, Comparable, Runnable.

What is user defined exception?

To handle situations specific to our applications we go for User Defined Exceptions.

and are defined by User using throw keyword.

What is the difference between process and threads?

Process is a heavy weight task and is more cost.

Thread is a light weight task which is of low cost.

A Program can contain more than one thread.

A program under execution is called as process.