Arrays
Thus Arrays in java are actual
objects that can be passed around and treated just like other objects. Arrays can contain any type of value (base
types or objects) but you cant store different types in a single array. Hence Arrays are can be defined as the set of
related data stored in a single variable.
There are three steps to create an array in Java.
1)
Declare a variable to hold the array.
2)
Create a new array object and assign it to be the array
variable.
3)
Store things in that array.
Declaring Array Variables
The first step to creating an array
is creating a variable that will hold the array, just as you would any other
variables. Array variables indicate type
of object array will hold, and the name of the array, followed by empty
brackets( [ ] ).
For example:
Point hits ( [ ] );
Int temps ( [ ] );
Creating array objects
There are two ways of achieving
this:
1)
Using
new.
For example :
String [] names
= new String[10];
When you create
an array object using new, all its elements are initialized for you. ( 0 for
numeric arrays, false for Boolean, ‘\0’ for character arrays, and null for
everything else).
2)
Directly
initializing contents of that array.
We can also
create and initialize an array at same time.
For example:
String[ ]
cities ={“Mumbai”, “Delhi ”, “Madras ”,
“Calcutta ”};
Block Statements
A block statement is a group of
other statements surrounded by braces ( { } ).
You can use a block anywhere a single statement would go, and the new
block creates a new local scope for the statements inside it. This means that you can declare and use local
variables inside a block, and those variables will cease to exist after the
block is finished executing.
For example in the following
example a block is inside a method definition that declares a new variable
y. You can not use y outside the block
in which it is declared.
void testblock( ){
int x =10;
{
int y = 50;
System.out.println(“Inside the
block”);
System.out.println(“ X ” + x);
System.out.println(“ Y ” + y);
}// Block Ends;
}
Control Flow Statements
If Conditions
The if conditional, which enables
you to execute different bits of code based on a simple test in java, is nearly
identical to if statements in C language.
For example:
if (x>y)
System.out.println( “X is Greater
than Y”);
The optional else keyword provides
the statement to execute if the test is
false.
For example:
if( x>y)
System.out.println(“ X is Greater
than Y”);
else
System.out.println(“ Y is Greater
than X”);
Example 1(Testing If)
class IfClass{
public static void main(String
args[]){
int a=50;
int b=100;
int c;
if (a>b){
c=a-b;
System.out.println("After
Deducting B From A" + c);
}
if (b>a){
c=b-a;
System.out.println("After
Deducting A From B" + c);
}
}
}
Switch Condition
The switch or case statements is
an alternative to nested ifs. It behaves
as it does in C.
switch (test){
case valueone:
resultOne;
break;
case valueTwo;
resultTwo;
break;
}
Example 2(Testing Switch)
public static void main(String[] args) {
String Signal;
switch (colors) {
case 1:
Signal = "Yellow";
break;
case 2:
Signal = "Red";
break;
case 3:
Signal = "Green";
break;
default:
Signal = "Invalid Signal";
break;
}
System.out.println(Signal);
}
}
for Loops
The for loop, as in C repeats
statements or block of statements some number of times until a condition is
matched. For loops are frequently used
for simple iteration in which you repeat a block of statements a certain number
of times and then stop. But you can use
for just any kind of loop.
Syntax: For (initialization;
test; increment){
statements;
}
For example
String strArray [ ] = new
String[10];
int i;
(for I =0; i<=strArray.length;
i++)
{
strArray[i] = “ “;
}
while Loop
while and do loops, like for
loops, enable block of Java code to be executed repeatedly until specific
condition is met.
Syntax: while(condition){
statements;
-
- - - -
-
- - - -
}
do…while Loop
do-while loop works similar to
the while loop except that do-while loop executes at least once even if the
condition is not true.
Syntax:
do{
statements;
-
- - - -
-
- - - -
} while(condition);
Breaking out of Loops
In all the loops, the loop ends when the condition you
are testing, is met. If something odd
occurs within the body of the loop and if you want to exit the loop early use
break keyword. In switch statement we
use break to stop the execution of the switch.
The break keyword when used with a loop, does the same thing, it
immediately stops execution of current loop and the program merely continues
executing next statement after the loop.
Practical Examples
Example 1
A program to generate integers
between 1 and N that are divisible by D, where N and D are to be given as
command line Arguments.
class Multiples{
public static void main(String []
args){
int value,divisor,val,div;
if(args.length==0){
System.out.println("USage :
java Multiples are ");
System.exit(0);
}
else{
System.out.print("Program
generates Integers Between ");
val=Integer.parseInt(args[0]);
div=Integer.parseInt(args[1]);
System.out.println(" 1 to
" + val + " Divisible by " + div);
if(val<1)
System.out.println("Value
Can not be Less than one ");
if(div<1)
System.out.println("Value
Can not be Less than one ");
else{
System.out.println("\t");
for(int i=1;i<=val;i++)
if((i%div)==0)
System.out.print(i
+"\t");
}
}
}
}
Example 2
A program to calculate maximum
height reached by a ball that is thrown perpendicular from ground surface at a
velocity of 20 mats/sec.
import java.io.*;
class Height{
public static void main(String []
args){
final double GraAcc = 9.8;
double velocity
=0,time=0,height=0;
InputStreamReader isr= new
InputStreamReader(System.in);
BufferedReader br= new
BufferedReader(isr);
System.out.println("
");
System.out.println("Calculating
Distance Traversed By a Ball ");
System.out.print("**********************************************
");
try{
System.out.println("\n");
System.out.println("Enter
value for The Valocity ");
velocity=Double.valueOf(br.readLine(
)).doubleValue( );
System.out.println("Enter
value for Time To Reach that Height ");
time=Double.valueOf(br.readLine(
)).doubleValue( );
height=velocity*time+(0.5*GraAcc*time*time);
}
catch(IOException ioe){
System.out.println("\n");
System.out.println("Input
Exception Caught "+ ioe);
}
System.out.print("The Height
Reached By the Ball is " + height+" Metrees.");
System.out.println("
");
}
}
Example 3 Fibonacci Series
import java.io.*;
import java.text.*;
class Fibonacci{
public static void main(String [] args){
InputStreamReader
isr= new InputStreamReader(System.in);
BufferedReader
br= new BufferedReader(isr);
int
last=1,next=1,sum=0,num;
try{
System.out.println("
");
System.out.println("Enter
length up to which calculation is to be done
");
num=Integer.parseInt(br.readLine(
));
System.out.println("
");
System.out.println("Fibonacci
Series up to number "+ num);
System.out.print(last+"\t"
+ next);
int
i =0;
while(i<num){
sum=last+next;
System.out.print("\t"+sum);
last=next;
next=sum;
i++;
}
}
System.out.println("Input
Exception Caught "+ ioe);
}
}
}
Example 4 Array Program
class Arrey
{
String[]
firstname={"Sandhya","Devender","Arti","Leela","Seema"};
String[] lastname= new
String[firstname.length];
void printname( )
{
int i=0;
System.out.println(firstname[i] +
" "+lastname[i]);
i++;
System.out.println(firstname[i]+"
" +lastname[i]);
i++;
System.out.println(firstname[i]+"
" +lastname[i]);
i++;
System.out.println(firstname[i]+"
" +lastname[i]);
i++;
}
public static void main(String
arguments[])
{
Arrey a =new Arrey( );
a.printname( );
System.out.println(".......");
a.lastname[0]
="Chatarji";
a.lastname[1] =
"Upadhyay";
a.lastname[2] =
"Prabhu";
a.lastname[3] = "Day";
a.lastname[4]
="Madhavi";
a.printname( );
}
}
Example 5 IfElse Construct
Class ifelse{
public static void main(String
arguments[])
{
int a =10;
if(a%2 ==0)
System.out.println(a + "is
even Number “);
else
System.out.println(a + "is
Odd Number “);
}
}
Example 6 Do Loop
class DoLoop{
public static void main (String arguments[]){
int x = 1 ;
do{
System.out.println("Looping,Round"+
x);
x++;
}
while(x<=10);
}
}
Example 7 While Loop
class WhileDemo{
public static void main (String
arguments[] )
{
int a=10, count =0;
while ( a<=20)
{
System.out.println("a = “ +
a + “\t");
count++;
a++;
}
System.out.println("While
Loop Executed" + count + “times”);
}
}
Example 8 For Loop
class ForDemo{
public static void main (String
arguments[] )
{
for(int i=1; i<=5 ; i++)
System.out.println("Value of
I is ” + i);
}
}
Example 9 Switch Construct
class Month {
public static void main(String[] args) {
int mmonth = 12;
String month;
switch (mmonth) {
case 1:
month = "January";
break;
case 2:
month = "February";
break;
case 3:
month = "March";
break;
case 4:
month = "April";
break;
case 5:
month = "May";
break;
case 6:
month = "June";
break;
case 7:
month = "July";
break;
case 8:
month = "August";
break;
case 9:
month = "September";
break;
case 10:
month = "October";
break;
case 11:
month = "November";
break;
case 12:
month = "December";
break;
day = "Invalid day";
break;
}
System.out.println(month);
}
}
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