Check whether a number is prime or not with output
import java.util.*;
public class PrimeNumber
{
public static void main(String[] args)
{
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter a number: ");
int num = scanner.nextInt();
PrimeNumber primeNum = new PrimeNumber();
if ( primeNum.isPrime(num) )
{
System.out.printf("\n Result: The number %d is Prime", num);
}
else
{
System.out.printf("\n Result: The number %d is not Prime", num);
}
}
public boolean isPrime(int num)
{
if ( num < 2 ) return false;
for (int i = 2; i <= Math.sqrt(num); i++)
{
if ( num % i == 0 )
{
return false;
}
}
return true;
}
}
Prime numbers upto given number using for loop
import java.util.*;
public class PrimeNumber
{
public static void main(String[] args)
{
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter a number: ");
int num = scanner.nextInt();
if ( num < 2 )
{
System.out.println("\n There are no Prime Numbers available");
System.exit(0);
}
System.out.printf("\n The Prime Numbers from 1 to %d are: \n 2", num);
PrimeNumber primeNum = new PrimeNumber();
for (int i = 3; i <= num; i++)
{
if ( primeNum.isPrime(i) )
{
System.out.print(", " + i);
}
}
}
public boolean isPrime(int num)
{
if ( num < 2 ) return false;
for (int i = 2; i <= Math.sqrt(num); i++)
{
if ( num % i == 0 )
{
return false;
}
}
return true;
}
}
Strings vs
StringBuffer vs Stringbuilder with to string()
class Employee
{
int empno;
String ename;
String job;
String hireDate;
int sal;
public Employee(int empno, String ename, String job,String hireDate, int sal)
{
this.empno = empno;
this.ename = ename;
this.job = job;
this.hireDate = hireDate;
this.sal = sal;
}
public String toString()
{
String str = " Employee [ empno=" + empno
+ " , ename=" + ename
+ " , job=" + job
+ " , hireDate=" + hireDate
+ " , sal=$" + sal
+ " ]";
return str;
}
}
Why Strings and Wrapper classes are immutable and final in java
class WhyMutable
{
public static void main(String[] args)
{
String name = "Parker";
Double sal = 60000.00;
displayTax(name, sal);
}
static void displayTax(String name, Double num)
{
name = "Hello " + name.concat("!");
num = num * 30 / 100;
System.out.println(name + " You have to pay tax $" + num);
}
}
Exception
handling in java
import java.io.*;
class Demo1
public static FileInputStream f1(String fileName)throws FileNotFoundException
{
FileInputStream fis = new FileInputStream(fileName);
System.out.println("f1: File input stream created");
return fis;
}
public static FileInputStream f2(String fileName)
{
FileInputStream fis = null;
try
{
fis = new FileInputStream(fileName);
}
catch (FileNotFoundException ex)
{
System.out.println("f2: Oops, FileNotFoundException caught");
}
finally
{
System.out.println("f2: finally block");
}
System.out.println("f2: Returning from f2");
return fis;
}
public static void main(String args[])
{
FileInputStream fis1 = null;
FileInputStream fis2 = null;
String fileName = "foo.bar";
String fileName = null;
System.out.println( "main: Starting " + Demo1.class.getName()
+ " with file name = " + fileName);
try
{
fis1 = f1(fileName);
}
catch (FileNotFoundException ex)
{
System.out.println("main: Oops, FileNotFoundException caught");
}
catch (Exception ex)
{
System.out.println("main: Oops, genreal exception caught");
}
fis2 = f2(fileName);
System.out.println("main: " + Demo1.class.getName() + " ended");
}
}
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