• Program:

public class MultiplyTwoNumbers {

    public static void main(String[] args) {

        float first = 3.4f;
        float second = 1.5f;

        float product = first * second;

        System.out.println("The product is: " + product);
    }
}

• Output:

The product is: 5.1

• A century year is a year ending with 00.  A century year is a leap year only if it is divisible by 400.
• A leap year (except a century year) can be identified if it is exactly divisible by 4.
• A century year should be divisible by 4 and 100 both.
• A non-century year should be divisible only by 4.

• Program:

public class Main {

  public static void main(String[] args) {

    // year to be checked
    int year = 2011;
    boolean leap = false;

    // if the year is divided by 4
    if (year % 4 == 0) {

      // if the year is century
      if (year % 100 == 0) {

        // if year is divided by 400
        // then it is a leap year
        if (year % 400 == 0)
          leap = true;
        else
          leap = false;
      }
      
      // if the year is not century
      else
        leap = true;
    }
    
    else
      leap = false;

    if (leap)
      System.out.println(year + " is a leap year.");
    else
      System.out.println(year + " is not a leap year.");
  }
}

• Output:

2011 is not a leap year

--- Another example ---

2012 is a leap year

• if determinant > 0, roots are real and different
• if determinant < 0, roots are complex and different
• if determinant == 0, roots are real and equal

• Program:

public class Main {

  public static void main(String[] args) {

    // value a, b, and c
    double a = 4.6, b = 2, c = 4.2;
    double root1, root2;

    // calculate the determinant (b2 - 4ac)
    double determinant = b * b - 4 * a * c;

    // check if determinant is greater than 0
    if (determinant > 0) {

      // two real and distinct roots
      root1 = (-b + Math.sqrt(determinant)) / (2 * a);
      root2 = (-b - Math.sqrt(determinant)) / (2 * a);

      System.out.format("root1 = %.2f and root2 = %.2f", root1, root2);
    }

    // check if determinant is equal to 0
    else if (determinant == 0) {

      // two real and equal roots
      // determinant is equal to 0
      // so -b + 0 == -b
      root1 = root2 = -b / (2 * a);
      System.out.format("root1 = root2 = %.2f;", root1);
    }

    // if determinant is less than zero
    else {

      // roots are complex number and distinct
      double real = -b / (2 * a);
      double imaginary = Math.sqrt(-determinant) / (2 * a);
      System.out.format("root1 = %.2f+%.2fi", real, imaginary);
      System.out.format("\nroot2 = %.2f-%.2fi", real, imaginary);
    }
  }
}

• Output:

root1 = -0.22+0.93i
root2 = -0.22-0.93i

• If n1 is greater or equals to both n2 and n3, n1 is the largest.
• If n2 is greater or equals to both n1 and n3, n2 is the greatest.
• Else, n3 is the greatest.

• Program:

public class Largest {

    public static void main(String[] args) {

        double n1 = -6.6, n2 = 1.3, n3 = 3.5;

        if( n1 >= n2 && n1 >= n3)
            System.out.println(n1 + " is the largest number.");

        else if (n2 >= n1 && n2 >= n3)
            System.out.println(n2 + " is the largest number.");

        else
            System.out.println(n3 + " is the largest number.");
    }
}

• Output:

3.5 is the largest number.

• Program:

public class VowelConsonant {

    public static void main(String[] args) {

        char ch = 'o';

        if(ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u' )
            System.out.println(ch + " is vowel");
        else
            System.out.println(ch + " is consonant");

    }
}                                     

• Output:

o is vowel

• Program:

import java.util.Scanner;

public class EvenOdd {

    public static void main(String[] args) {

        Scanner reader = new Scanner(System.in);

        System.out.print("Enter a number: ");
        int num = reader.nextInt();

        if(num % 2 == 0)
            System.out.println(num + " is even");
        else
            System.out.println(num + " is odd");
    }
}

• Output:

Enter a number: 16
16 is even

--- Second Example ---

Enter a number: 27
27 is odd

• Program:

public class SwapNumbers {

    public static void main(String[] args) {

        float first = 2.60f, sec = 4.44f;

        System.out.println("--Before swapping the numbers--");
        System.out.println("First number = " + first);
        System.out.println("Second number = " + sec);

        // Value of first is assigned to temporary
        float temporary = first;

        // Value of sec is assigned to first
        first = sec;

        // Value of temporary (which contains the initial value of first) is assigned to sec 
        sec = temporary;

        System.out.println("--After swapping the numbers--");
        System.out.println("First number = " + first);
        System.out.println("Second number = " + sec);
    }
}

• Output:

--Before swapping the numbers--
First number = 2.6
Second number = 4.44
--After swapping the numbers--
First number = 4.44
Second number = 2.6

• Step:

1. Assign first to a temporary variable: temporary = first
2. Assign second to first: first = second
3. Assign temp to second: second = temporary