Write a java program that finds and stores the factorials of numbers between and including 3 and 10 in an array and calculates the average of the factorials from the array.

/*
For more exercises,
visit shegertech.blogspot.com
or
shegertech.com
Author: Eyasu M.
Email: eyasu@india.com
*/

public class FactorialAverage {
    public static void main(String[] args) {
        int factorial;
        double sum = 0;
        int[] x = new int[8];
        for (int i = 3, k = 0; i <= 10; i++, k++) {
            factorial = 1;
            for (int y = 1; y <= i; y++) {
                factorial *= y;
            }
            x[k] = factorial;
            sum += x[k];
        }
        System.out.println(sum / x.length);
    }
}

Output

Exponent Program

/*
A program that displays the value of a number raised to the power of a number.Created by Eyasu Mulugeta A.K.A BlackDiamond0014 on 6/23/2017.
eyasu@india.com
*/
import java.util.Scanner;
import static java.lang.Math.pow;

public class ExponentProgram {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        double base, exponent;
        System.out.print("Enter the base : ");
        base=in.nextDouble();
        System.out.println();
        System.out.print("Enter the exponent : ");
        exponent=in.nextDouble();

        System.out.println("\n"+base+" raised to "+exponent+" is "+
                pow(base,exponent));
    }
}

Factor Program

/*A program that displays the factors of a number.
Created by Eyasu Mulugeta A.K.A BlackDiamond0014 on 6/23/2017.
eyasu@india.com
*/
import java.util.ArrayList;
import java.util.Scanner;
public class FactorProgram {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int num=0, size;
        System.out.print("Enter a number to find its factors : ");
        num = in.nextInt();
        ArrayList<Integer> factors = new ArrayList<Integer>();
        System.out.println();
        System.out.print("The factors of " + num + " are ");
        for (int i = 1, j = 0; i <= num; i++, j++) {
            if (num % i != 0)
                continue;
            factors.add(i);
        }
        for (int k:factors) {
            System.out.print(k);
            if(k==num){
                break;
            }
            System.out.print( ", ");
        }
    }
}

Multiplication Table Program

/*A program that displays the multiplication table.
Created by Eyasu Mulugeta A.K.A BlackDiamond0014 on 6/23/2017.
eyasu@india.com*/

public class MultiplicationTable {
    public static void main(String[] args) {
        int j, k;
        System.out.print("x");
        for (int m = 0; m <= 12; m++)
            System.out.print("\t" + m + "\t");
        for (int i = 0; i <= 12; i++) {
            System.out.print("\n" + i);
            for (j = 0; j <= 12; j++) {
                System.out.print("\t" + (i * j) + "\t");
            }

        }
    }
}

Square Root Program

/*
A program that displays the square root of a number.
Created by Eyasu Mulugeta A.K.A BlackDiamond0014 on 6/23/2017.
eyasu@india.com
*/

import java.util.Scanner;

import static java.lang.Math.sqrt;

public class SquareRoots {
    public static void main(String[] args) {
        //we used the Scanner class to create an object to input data        
        Scanner in = new Scanner(System.in);
        int num=0;

        System.out.print("Please input a number : ");
        num = in.nextInt();

        System.out.println("The square root of "+num+" is "+sqrt(num));

    }
}

Difference Program

/*A program that displays the difference between two integer numbers.
Created by Eyasu Mulugeta A.K.A BlackDiamond0014 on 6/23/2017.
eyasu@india.com


*/import java.util.Scanner;
public class SubtractTwoNumbers {
    public static void main(String[] args) {
        int num1, num2;

        Scanner s = new Scanner(System.in);

        System.out.println("\n\n\t\t\t# # # # Subtraction Program # # # #\n\n");
        System.out.print("Please enter the first number : ");
        num1=s.nextInt();
        System.out.print("Please enter the second number : ");
        num2=s.nextInt();

        System.out.println("\nThe difference of "+num1+" and "+num2+
                " is "+(num1-num2)+".");
    }
}

Sum Program

/*
A program that displays the sum of two integer numbers.
Created by Eyasu Mulugeta A.K.A BlackDiamond0014 on 6/23/2017.
eyasu@india.com
*/

import java.util.Scanner;
public class AddTwoNumbers {
    public static void main(String[] args) {
        int num1, num2;

        Scanner s = new Scanner(System.in);

        System.out.println("\n\n\t\t\t# # # # Sum Program # # # #\n\n");
        System.out.print("Please enter the first number : ");
        num1=s.nextInt();
        System.out.print("Please enter the second number : ");
        num2=s.nextInt();

        System.out.println("\nThe sum of "+num1+" and "+num2+
                " is "+(num1+num2)+".");
    }
}

Write a program that checks whether a string is palindrome or not.

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 */

import java.util.Scanner;

public class Q2Solution {
    public static void main(String[] args){
        String original, reverse = "";
        Scanner in = new Scanner(System.in);

        System.out.print("Enter a string to check if it is a palindrome : ");
        original = in.nextLine();

        int length = original.length();

        for ( int i = length - 1; i >= 0; i-- )
            reverse = reverse + original.charAt(i);

        if (original.equals(reverse))
            System.out.println("Entered string is a palindrome.");
        else
            System.out.println("Entered string is not a palindrome.");

    }
}

Find all twin prime numbers less than 100.

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 * Chapter 8, Example 3
 */

public class Q3Solution {

    public boolean is_Prime(long n) {

        if (n < 2)
            return false;

        for (int i = 2; i <= n / 2; i++) {

            if (n % i == 0)
                return false;
        }
        return true;
    }
    public static void main(String[] args) {

        Q3Solution q3 = new Q3Solution();

        for (int i = 2; i < 100; i++) {
            if (q3.is_Prime(i) && q3.is_Prime(i + 2)) {
                System.out.printf("(%d, %d)\n", i, i + 2);
            }
        }
    }

}

Write a Java method to check whether a year (integer) entered by the user is a leap year or not.

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 * Chapter 8, Exercise 2
 */

public class Q2Solution {
    public static void main(String[] args){
        int year = 2008;

        if((year % 400 == 0) || ((year % 4 == 0) && (year % 100 != 0)))
            System.out.println("Year " + year + " is a leap year");
        else
            System.out.println("Year " + year + " is not a leap year");
    }
}

Write a Java method to find the smallest number among three numbers using arrays and methods.

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 * Chapter 8, Exercise 1
 */

public class Q1Solution {

void smallestNumber(int[] arr){
    int smallestNumber =arr[0];
    for (int i=1;i< arr.length;i++){
        if (smallestNumber>arr[i]){
            smallestNumber=arr[i];
        }
    }
    System.out.println("The smallest number in tbe array is "+ smallestNumber);
}
    public static void main(String[] args) {

        int[] arr={55, 34, 11, 87, 29};
        Q1Solution q1 = new Q1Solution();
        q1.smallestNumber(arr);
     }
}

Write a guess number game.

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 */

import java.util.Random;
import java.util.Scanner;

public class Q2Solution {
    public static void main(String[] args){

        System.out.println("Pick a number: ");

        Scanner inputnum = new Scanner(System.in);
        int maxnum;
        maxnum = inputnum.nextInt();

        Random rand = new Random();
        int number = rand.nextInt(maxnum);
        int tries = 0;
        Scanner input = new Scanner(System.in);
        int guess;
        boolean win = false;

        while (win == false){

            System.out.println("Guess a number between 1 and "+ maxnum +": ");
            guess = input.nextInt();
            tries++;

            if (guess == number){
                win = true;
               
            }

            else if(guess < number){
                System.out.println("Number is to low, tray again");
               
            }

            else if(guess > number){
                System.out.println("Number is to high, try again");
               
            }

        }

        System.out.println("You win!");
        System.out.println("It took you "+ tries + " tries.");

    }
}

Write a program that generates numbers between the range 0-25 and display the average of the prime numbers that are generated.

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 * Chapter 7, Exercise 1
 */

public class Q1Solution {

    double averageOfPrimeNumbers() {
        double average = 0.0d;
        boolean flag;
        int half = 0, sum = 0, count=0;
        for (int i = 2; i <= 10; i++) {
            half = i / 2;
            flag = true;
            for (int j = 2; j <= half; j++) {
                if (i % j == 0) {
                    flag = false;
                }
            }
            if (flag) {
                sum += i;
                count++;
            }
        }

        average = (double) sum / count;
        return average;
    }

    public static void main(String[] args) {

        Q1Solution q1 = new Q1Solution();
        double average = q1.averageOfPrimeNumbers();
        System.out.println("The average is " + average);
    }
}

Write a program that will ask the user to input three integer values from the keyboard. Then it will print the smallest and largest of those numbers using functions.

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 */

 public class Q2Solution {
    void compare(int num1, int num2, int num3) {

        int smallest = 0, largest = 0;

        if(num1>num2 && num1>num3)
            largest = num1;
        else if (num2>num1 && num2>num3)
            largest= num2;
        else
            largest = num3;

        System.out.println("Largest number = " + largest);

        if(num1<num2 && num1<num3)
            smallest = num1;
        else if (num2<num1 && num2<num3)
            smallest = num2;
        else
            smallest =num3;

        System.out.println("Smallest number = " + smallest);

    }

    public static void main(String[] args) {
        int n1 = 9, n2 = 5, n3 = 4;

        Q2Solution q2 = new Q2Solution();
        q2.compare(n1, n2, n3);
    }
}

Write a Java basic calculator.

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 * Chapter 6, Exercise 1
 */

import java.util.Scanner;

public class Q1Solution {

    private float firstOperannd;
    private float secondOperannd;
    private float result;
    private int operator;
    private Scanner input = new Scanner(System.in);
    private boolean exitCalculator = false;

    public void startCalculator() {
        while (!exitCalculator) {

            System.out.print("Enter 1 for addition \n"
                    + "Enter 2 for subtraction \n"
                    + "Enter 3 for multiplication \n"
                    + "Enter 4 for division \n" + "Enter 0 for Exit"+"\n\nInput Menu number : ");
            operator = input.nextInt();

            switch (operator) {
                case 1:
                    result = add();
                    System.out.println("\nResult is " + result+"\n");
                    break;

                case 2:
                    result = subtract();
                    System.out.println("\nResult is " + result+"\n");
                    break;

                case 3:
                    result = multiply();
                    System.out.println("\nResult is " + result+"\n");
                    break;

                case 4:
                    result = divide();
                    System.out.println("\nResult is " + result+"\n");
                    break;

                case 0:
                    exitCalculator = true;
                    System.out.println("Calculator program Terminated \n");
                    break;

                default:
                    System.out.println("Please provide proper input \n");

            }
        }
    }

    private float add() {
        System.out.print("\nEnter first number : ");
        firstOperannd = input.nextInt();
        System.out.print("\nEnter second number : ");
        secondOperannd = input.nextInt();
        return firstOperannd + secondOperannd;
    }

    private float subtract() {
        System.out.print("\nEnter first number : ");
        firstOperannd = input.nextInt();
        System.out.print("\nEnter second number : ");
        secondOperannd = input.nextInt();
        return firstOperannd - secondOperannd;
    }

    private float multiply() {
        System.out.print("\nEnter first number : ");
        firstOperannd = input.nextInt();
        System.out.print("\nEnter second number : ");
        secondOperannd = input.nextInt();
        return firstOperannd * secondOperannd;
    }

    private float divide() {
        System.out.print("\nEnter first number : ");
        firstOperannd = input.nextInt();
        System.out.print("\nEnter second number : ");
        secondOperannd = input.nextInt();
        return firstOperannd / secondOperannd;
    }

    public static void main(String[] args) {
        Calculation c= new Calculation();
        c.startCalculator();
    }
}

Write a Java program that will print the pattern as shown below.

****
*****
*******
*********
*********
*******
*****
****


/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 * Chapter 5, Exercise 4
 */

public class Q4Solution {
    public static void main(String[] args) {
        int i=0;
        int j=0;

        for(i=1;i<=9;i=i+2){
            for(j=1;j<=i;++j)
                System.out.print("*");

            System.out.print("\n");

        }
        for(i=9;i>=1;i=i-2){
            for(j=i;j>=1;--j)
                System.out.print("*");

            System.out.print("\n");


        }

        System.out.print("\n");

    }
}

Write a program that accepts a number from the user and tells whether the number is a prime number.

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 * Chapter 5, Exercise 3
 */

import java.util.Scanner;

public class Q3Solution {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        int num = 0, half = 0;
        boolean flag = false;

        System.out.print("Enter a positive integer number : ");
        num = in.nextInt();
        half = num / 2;
        if (num > 0) {
            for (int i = 2; i <= half; i++) {
                if (num % i == 0) {
                    flag = true;
                }
            }
            if (flag) {
                System.out.println(num + " is not a prime number.");
            } else {
                System.out.println(num + " is a prime number.");
            }
        } else {
            System.out.println("Please enter a non-negative integer number.");
        }
    }
}

Write a program that displays the numbers between 1 and 10 in reverse order(descending order).

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 * Chapter 5, Exercise 2
 */

import java.util.Scanner;

public class Q2Solution {
    public static void main(String[] args) {
        for (int i=10; i>0;i--){
            System.out.println(i);
        }
    }
}

Write a java program that accepts a number from the user and tells whether it is a perfect number or not.

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 * Chapter 5, Exercise 1
 */

import java.util.Scanner;

public class Q1Solution {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int num1 = 0, sum=0;
        System.out.print("Enter the number : ");
        num1 = in.nextInt();

        for (int i=1; i<num1;i++){
            if (num1%i==0){
                sum+=i;
            }
        }
        if(sum==num1){
            System.out.println(num1+" is a perfect number");
        }
        else {
            System.out.println(num1+ " is not a perfect number");
        }
    }
}

Write a Java program that prompts the user to input three integer values and find the greatest value of the three values.

/**
 * Created by Jo on 7/10/2017.
 * For more exercises and lessons, visit http://shegertech.blogspot.com/
 * Chapter 4, Exercise 3
 */

import java.util.Scanner;

public class Q3Solution {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int num1 = 0, num2 = 0, num3 = 0, max = 0;

        System.out.print("First value : ");
        num1 = in.nextInt();
        System.out.print("Second value : ");
        num2 = in.nextInt();
        System.out.print("Third value : ");
        num3 = in.nextInt();

        if (num1 > num2 && num1 > num3) {
            max = num1;
            System.out.println("The maximum value is " + max);
        } else if (num2 > num1 && num2>num3) {
            max= num2;
            System.out.println("The maximum value is " + max);
        }
        else{
            max = num3;
            System.out.println("The maximum value is " + max);
        }
    }
}