Java Programming

You do not use pointers in Java because the language designers decided to abstract memory management to a higher level in Java than in C. The reason for this is that it is easy to make mistakes using pointers and other lower level memory management techniques. These mistakes can lead to bugs. hard to read code, memory leaks that waste system resources, and security issues. Instead for the most part Java takes care of memory management for the user who can instead specify behavior though the object oriented techniques that are safer and easier to understand. The downside is that the programmers lose some control and flexibility in using memory. Also, programs using Java take a small performance hit in some cases because of the extra work Java has to do to manage memory itself.

They are, however in Java they are called references.

Because it supports Web-oriented architecture (If we will discuss about J2EE/ Java for Enterprise Edition). It is HTML, the language of the Internet, its protocol HTTP provides standard operating procedure for transfer of info between client and web server.


Java is not "the language of the Internet". For humans, English is the language of the Internet since it is what a majority uses to communicate, because it is the language which the IETF uses to write standards and protocols, and because most Internet hardware is configured using software in English. For computers, HTML/SGML/XML, JavaScript and Flash are all Internet languages of sorts, and all use English verbs. Java is used to implement some back-end systems, notably from Apache and Sun, but so are C, C++, Tcl, Perl, and dozens of others.


Whomever is trying to teach you that Java is the language of the Internet is relying too much on advertisements from the late 1990s for their information.

A Class is a template from which Objects are created, in much the same way as a plan of a building is a template from which a building is created... just as the building plan is a piece of paper and not a building, so a Class is not an Object.

The code for a Class describes the way in which an Object should behave when particular methods are invoked.

Swing is a package in Java which contains tools for building GUI application. Swing is a part of Java's foundation classes.

On a Windows platform the online Java Runtime Environment (JRE) installer is approximately 0.86 MB and the installed size on disk is about 98MB.

The downloadable full Windows offline JRE installer is larger ~30.2 MB and for MacOS ~50 MB.

An abstract class is designed to provide function and organization to subclasses without ever existing as an object itself. In other words, it is a glorified template, an abstraction for subclasses, and would be illogical to instantiate.

As an example, imagine that a zoo wanted to make separate classes representing each of its animals, but wanted them to all have some common features like a variable for life expectancy or a method to project feeding costs. To force every class to implement this functionality, the programmer may create an abstract class called Animal that each subclass would extend. However, would it ever make sense to create an Animal? No, because an Animal does not exist anywhere in the zoo - an Alligator however might.

Return a value in the constructor is senseless, because a constructor is used to initialize a object instance and not to perform a task or a operation. When we call a constructor we used a sentence like this:

MyClass var = new MyClass();

Then when we execute the above line the constructor return ('create') a new object of the type 'MyClass'. If this call could return an other type, for example an Integer, the constructor is considered a normal method, and if there are not more constructors a empty default constructor for MyClass is defined by the java compiler.

public class MyClass{

// The java compiler will insert a real constructor here

public Integer MyClass(){ //This isn't a constructor, only a simple method

return new Integer(1);

}

}

A class is simply the definition of a data type. A constructor is a special method of a class that is automatically invoked whenever an object of that type is instantiated, and is used to initialise the object's data members.

The value what we pass in the constructor is know as argument.you can look into the example given below to make it more clear.

class Test

{

Test(int a,int b)

{

int c=a+b;

System,out.println("the value of "+c);

}

}

public class testMain{

Public static void main(String args[])

{

Test t=new Test(10,20);

//here 10 and 20 are the arguments and a,b are parameters....

}

}

i hope this will help u

Kumar Ashish

Static data members are different from automatic ones in the way that their lifetime is equals to the lifetime of your program. Even if you have declared static members inside of function (class) other than main();

High Level Language:

High level language are easier to use and less technical skills are required to do a program. It is very useful where textual data is given priority. Troubleshooting doesn't takes a longer time. We get to know the errors very easily.

Low Level Language:

Low level language are not easily read at a glance and very high technical skill are required to do a program. Troubleshooting takes a longer time. They can produce stunning graphics.

Java is used just about everywhere. Your phone, television, computer etc. Java is the most popular programming language. Example of Java:

import java.io.*;

import java.util.*;

public class Calculator

{

public static void main(String args[])

{

System.out.println("Make your arithmetic selection from the choices below:\n");

System.out.println(" 1. Addition");

System.out.println(" 2. Subtraction");

System.out.println(" 3. Multiplication");

System.out.println(" 4. Division\n");

System.out.print(" Your choice? ");

Scanner kbReader = new Scanner(System.in);

int choice = kbReader.nextInt();

if((choice<=4) && (choice>0))

{

System.out.print("\nEnter first operand. ");

double op1 = kbReader.nextDouble();

System.out.print("\nEnter second operand.");

double op2 = kbReader.nextDouble();

System.out.println("");

switch (choice)

{

case 1: //addition

System.out.println(op1 + " plus " + op2 + " = " + (op1 + op2) );

break;

case 2: //subtraction

System.out.println(op1 + " minus " + op2 + " = " + (op1 - op2) );

break;

case 3: //multiplication

System.out.println(op1 + " times " + op2 + " = " + (op1 * op2) );

break;

case 4: //division

System.out.println(op1 + " divided by " + op2 + " = " + (op1 / op2) );

}

}

else

{

System.out.println("Please enter a 1, 2, 3, or 4.");

}

}

}

* Prepared Statement is Pre-compiled class , but Statement is not. * So in PreparedStatement the execution will be faster. Actually when u submit a simple statement to the databse, at first the DBMS parses it and sends it back with the result, so again when u send the same statement again the DBMS server parses it and sends back the result so here a lot of time is wasted and because the statement is again parsed though it has been sent twice or thrice it consumes a lot of time and response will be slow.Prepared Statement is used when u want to execute a statement object many times. when u submit a PreparedStatement the DBMS server parses it and creates a execution plan. This e-plan can be used when u again send the same statement to the database.That is the DBMS server zest executes the compiled statement rather that executing it from first, hence we get an precompiled statement.And also the advanatge of using this PreparedStatement is it is used to send dynamic sql statements, which u can give values later than giving the values at the time of creation.

• Abstract class is built to promote inheritance whereas a final class is built to avoid inheritance
• An Abstract class can be extended by another class whereas a final class cannot be extended

#include <iostream>

#include <stack>

using namespace std;

int prec (char ch){

// Gives precedence to different operators

switch (ch) {

case '^':

return 5;

case '/':

return 4;

case '*':

return 4;

case '+':

return 2;

case '-':

return 1;

default :

return 0;

}

}

bool isOperand(char ch){

// Finds out is a character is an operand or not

if ((ch>='0' && ch<='9') (ch>='a' && ch<='z'))

return true;

else

return false;

}

string postFix (string infix){

string pfix = "";

stack<char> opstack;

for (int i=0; i<infix.length(); i++){

// Scan character by character

if (isOperand(infix[i]))

{

pfix += infix[i];

}

else if (infix[i] ')')

{

// Retrace to last ( closure

while (opstack.top() != '(')

{

pfix += opstack.top();

opstack.pop();

}

// Remove the '(' found by while loop

opstack.pop();

}

A parameter or an argument is a value that is passed to a method so that the method can use that value in its processing.

Ex:

public String getName(String x){

return "Mr. " + x;

}

Here the method just prefixe's a Mr. with the value that is being passed to the method getName. The value X can be termed a parameter or an argument

You can stop an unhandled exception by handling it. When your program crashes it will tell you exactly where it crashed and what exception it ran into. Dealing with the exception is the hard part. Generally, you want to take one of two approaches. The first is to make sure that the exception cannot happen. You may, for example, have to validate data to make sure that your users aren't allowed to give input which would result in a division-by-zero exception. The second is to allow the exception to be thrown, but use a try-catch block to catch it and print out a useful message instead of crashing. The method you choose will depend on what your program is supposed to do, who is using it, what exceptions are being thrown, where they're being thrown, etc. There's no silver bullet solution for handling an exception.

public class Add { public staticvoid main(String[] args) { int value=12; intcount=0; int sum=0; while(count<=4) { sum+=value%10; value=value/10; count++; } System.out.print("The sum of the individual integers is= "+ sum); } }

/* gcc -ansi -Wall -Wextra -pedantic -s -static 0.c -o 0 */

#include <stdio.h>

int main ( )

{

int n , factorial = 1 ;

printf ( "enter the value of n\n") ;

scanf ( "%i" , & n ) ;

while ( n != 0 )

{

factorial *= n ;

n -- ;

}

printf ( "The factorial of n is\n%i\n" , factorial ) ;

return 0;

}

The simplest way of doing this is not very efficient, but provides a quick development time. You want to take all of the elements of the array, add them to a Set, then retrieve them as an array again. Note that this will probably not preserve the order of elements in the array.

{

Object[] originalArray; // let's pretend this contains the data that

// you want to delete duplicates from

Set newSet = new HashSet();

for (Object o : originalArray) {

newSet.add(o);

}

// originalArray is now equal to the array without duplicates

originalArray = newSet.toArray();

}

Now the efficient, and more correct, solution.

This one will create a new array of the correct size without duplicates.

{

Object[] originalArray; // again, pretend this contains our original data

// new temporary array to hold non-duplicate data

Object[] newArray = new Object[originalArray.length];

// current index in the new array (also the number of non-dup elements)

int currentIndex = 0;

// loop through the original array...

for (int i = 0; i < originalArray.length; ++i) {

// contains => true iff newArray contains originalArray[i]

boolean contains = false;

// search through newArray to see if it contains an element equal

// to the element in originalArray[i]

for(int j = 0; j <= currentIndex; ++j) {

// if the same element is found, don't add it to the new array

if(originalArray[i].equals(newArray[j])) {

contains = true;

break;

}

}

// if we didn't find a duplicate, add the new element to the new array

if(!contains) {

// note: you may want to use a copy constructor, or a .clone()

// here if the situation warrants more than a shallow copy

newArray[currentIndex] = originalArray[i];

++currentIndex;

}

}

// OPTIONAL

// resize newArray (using _newArray) so that we don't have any null references

Object[] _newArray = new Object[currentIndex];

System.arraycopy(newArray, 0, _newArray, 0, currentIndex);

}

public static void main(String[] args) { int val = 100; int val1 = 50; System.out.println("Number of digits in " + val + " is: " + new String(val + "").length()); System.out.println("Number of digits in " + val1 + " is: " + new String(val1 + "").length()); }

No. A method that is declared as private in a class is not inherited by any other class and hence if another class that extends this class declares a method with the same name and signature, it does not mean that this method is overridden. It is an entirely separate entity.

The throw keyword is used from within a method to "throw" an exception to the calling method. In order to throw an exception, the method signature must indicate that it will throw an exception. For example: public void foo() throws Exception { } When you want to actually throw the exception, you can do it a few different ways: throw new Exception("Exception message"); or from within a catch block ( catch(Exception ex) ): throw ex;