List of basic logical programs in Java

Logical programming is a programming paradigm that is largely based on formal logic. Logical programming is mostly asked in the interview by the interviewer to check the logical skills of the candidates. In this article, you will see the very basic and commonly asked logical programs in the interview with clear explanations such as,

  • Fibonacci series
  • Calculate the factorial
  • Check Prime number
  • Check Perfect number
  • Check Armstrong number
  • Reverse a number
  • Check Palindrome number
  • Swap two numbers

Fibonacci Series

Fibonacci series is a special type of series in which the next number is the sum of the previous two numbers. For example, 1 1 2 3 5 8 13 21…. up to a given number.

Solution #1 : Using Recursion

FibonacciSeriesWithRecursion.java

package com.javacodepoint.programs;
 
import java.util.Scanner;
 
public class FibonacciSeriesWithRecursion {
 
    // initiating first two numbers of the Fibonacci series
    static int number1 = 0;
    static int number2 = 1;
 
    public static void main(String[] args) {
 
        // Taking input from the user to print Fibonacci series up to how many numbers
 
        System.out.println("Enter number up to which Fibonacci series to print:");
 
        // Reading user input using Scanner object
        int upto = new Scanner(System.in).nextInt();
 
        // Printing first two numbers
        System.out.print(number1 + " " + number2);
 
        // Calling recursive function by decreasing 2 because two numbers are already printed
        printFibonacci(upto - 2);
 
    }
 
    /*
     * Recursive function
     */
    public static void printFibonacci(int count) {
 
        if (count > 0) {
            int nextNumber = number1 + number2;
            number1 = number2;
            number2 = nextNumber;
 
            System.out.print(" " + nextNumber);
 
            // Call the recursive function again
            printFibonacci(count - 1);
        }
    }
}

OUTPUT:

Enter number up to which Fibonacci series to print:
10
0 1 1 2 3 5 8 13 21 34

Solution #2 : Without Using Recursion

FibonacciSeries.java

package com.javacodepoint.programs;
 
import java.util.Scanner;
 
public class FibonacciSeries {
 
    public static void main(String[] args) {
 
        // Taking input from the user to print Fibonacci series up to how many numbers
 
        System.out.println("Enter number up to which Fibonacci series to print:");
 
        // Reading user input using Scanner object
        int upto = new Scanner(System.in).nextInt();
 
        // Initiating first two numbers of the Fibonacci series
        int number1 = 0;
        int number2 = 1;
 
        // Printing first two numbers
        System.out.print(number1 + " " + number2);
 
        // Start the loop from 3 because first two numbers are already printed
        for (int i = 3; i <= upto; i++) {
            int nextNumber = number1 + number2;
            System.out.print(" " + nextNumber);
            number1 = number2;
            number2 = nextNumber;
        }
    }
}

OUTPUT:

Enter number up to which Fibonacci series to print:
8
0 1 1 2 3 5 8 13

Calculate the factorial

The multiplication of all positive integers which are less than or equal to the given positive number is called the factorial of that given integer number.

Example #1, The factorial of the number 5 can be calculated as follow:

1 * 2 * 3 * 4 * 5 = 120

Example #2, The factorial of the number 8 can be calculated as follow:

1 * 2 * 3 * 4 * 5 * 6 * 7 * 8 = 40320

Solution #1 : Using Recursion

FactorialCalculation.java

package com.javacodepoint.programs;
 
import java.util.Scanner;
 
public class FactorialCalculation {
 
    public static void main(String[] args) {
 
        // Taking input from the user to calculate factorial for a given number
 
        System.out.println("Enter number to calculate factorial:");
 
        // Reading user input using Scanner object
        int number = new Scanner(System.in).nextInt();
         
        if(number < 0) {
            System.out.println("Please enter only positive interger number");
            return;
        }
         
        System.out.println("Factorial of "+number+" is : "+clculateFactorial(number));
 
    }
         
    /* 
     * Method to calculate factorial using recursion
     */
     
    public static int clculateFactorial(int number) {
         
        if(number == 0) {
            return 1;
        }
         
        return number * clculateFactorial(number-1);
    }
}

OUTPUT:

Enter number to calculate factorial:
5
Factorial of 5 is : 120

Solution #2 : Without Using Recursion

FactorialCalculation.java

package com.javacodepoint.programs;
 
import java.util.Scanner;
 
public class FactorialCalculation {
 
    public static void main(String[] args) {
 
        // Taking input from the user to calculate factorial for a given number
 
        System.out.println("Enter number to calculate factorial:");
 
        // Reading user input using Scanner object
        int number = new Scanner(System.in).nextInt();
         
        if(number < 0) {
            System.out.println("Please enter only positive interger number");
            return;
        }
         
        System.out.println("Factorial of "+number+" is : "+clculateFactorial(number));
 
    }
         
    /* 
     * Method to calculate factorial without recursion
     */
     
    public static int clculateFactorial(int number) {
         
        int factorial = 1;
         
        while(number != 0){
             
            factorial = factorial * number ;
            number--;
        }
         
        return factorial;
    }
}

OUTPUT:

Enter number to calculate factorial:
6
Factorial of 6 is : 720

Check Prime number

A Prime number is a number that is divisible by only 1 and itself. A prime number can’t be divided by zero, because numbers divided by zero are undefined. The smallest prime number is 2, which is also the only even prime.

Let’s see the logic to check whether a number is a prime number or not,

Solution

PrimeNumber.java

package com.javacodepoint.programs;

import java.util.Scanner;

public class PrimeNumber {

	public static void main(String[] args) {

		System.out.print("Enter an integer number:");

		// Reading user input using Scanner object
		int number = new Scanner(System.in).nextInt();
		
		if(number > 1 && checkPrime(number)) {
			System.out.println("The given number is a prime number.");
		}else {
			System.out.println("The given number is not a prime number.");
		}

	}
	
	/*
	 * Method to check whether number is prime or not
	 */
	
	public static boolean checkPrime(int number) {
		
		boolean isPrime = true;
		
		for(int i=2; i <= (number/2); i++ ) {
			
			if(number % i == 0) {
				isPrime = false;
				break;
			}
			
		}
		
		return isPrime;
		
	}
}

OUTPUT:

Enter an integer number:13
The given number is a prime number.

Check Perfect number

The Perfect Number is a special type of positive number. When the number is equal to the sum of its positive divisors excluding the number, it is called a Perfect Number.

For example, 28 is the perfect number because when we sum the divisors of 28, it will result in the same number. The divisors of 28 are 1, 2, 4, 7, and 14. 28 = 1 + 2 + 4 + 7 + 14
28 = 28

Let’s see the logic to check it,

Solution

package com.javacodepoint.programs;

public class CheckPerfectNumber {
    
    public static void main (String[] args){   
        
    	System.out.println("All Perfect numbers between 1 - 1000:");   
    	
        for (int i = 1; i < 1000; i++ ){   
            if (isPerfectNumber(i)) {
            	System.out.println( i +" is a perfect number");
            }   
        }  
    } 
    
    
    /*
     * Method that will return true when number will be perfect   
     */
    static boolean isPerfectNumber(int number) {   
        
    	int sum = 1;   
    
        // Finding all the divisors   
        for (int i = 2; i * i <= number; i++) {   
            if (number % i == 0) {   
                if(i * i != number) {   
                    sum = sum + i + number / i;   
                } else { 
                    sum = sum + i;  
                }
            }   
        }    
        
        // Checking whether the sum of all divisors and number both are equal or not  
        if (sum == number && number != 1) {  
            return true;   
        }
        
        return false;   
    }
}

OUTPUT:

All Perfect numbers between 1 – 1000:
6 is a perfect number
28 is a perfect number
496 is a perfect number

Check Armstrong number

A special positive number whose sum of cubes of its individual digit is equal to that number is called an Armstrong Number. 

Example #1,
The number 153 is an Armstrong number. It can be checked as follow:
(1)3 + (5)3 + (3)3 => 1 + 125 + 27 => 153

Example #2,
The number 371 is also an Armstrong number and It can be checked as follow:
(3)3 + (7)3 + (1)3 => 27 + 343 + 1 => 371

Let’s see the logic to check whether a number is an Armstrong number or not,

Solution

ArmstrongNumber.java

package com.javacodepoint.programs;

import java.util.Scanner;

public class ArmstrongNumber {

	public static void main(String[] args) {
		
		// Taking input from the user to check whether number is Armstrong

		System.out.println("Enter a number to check Armstrong :");

		// Reading user input using Scanner object
		int number = new Scanner(System.in).nextInt();
		
		if(checkArmstrong(number)) {
			System.out.println("The given number is an Armstrong number.");
		}else {
			System.out.println("The given number is not an Armstrong number.");
		}
		
	}
	
	/*
	 * Method to check Armstrong number
	 */
	public static boolean checkArmstrong(int number) {
	    
		int sumOfCube = 0;
		int temp = number;    
	    while(number > 0){
	    	
	    	//Getting last digit 
	        int a = number % 10;  
	        
	        //Removing last digit from number  
	        number = number / 10;  
	        
	        //Calculating sum of cubes of digits    
	        sumOfCube = sumOfCube + (a*a*a); 
	    } 
	    
	    if(temp == sumOfCube) {
	    	return true;
	    }
	    
	    return false;
	}

}

OUTPUT:

Enter a number to check Armstrong :
370
The given number is an Armstrong number.

Reverse a number

The reverse of a given number is simply called as when the number is 123, the reverse number should be 321. In java, there are multiple ways to calculate the reverse of a given number. Here we will discuss a simple way using a while loop.

Follow the below steps to calculate the reverse of a number,

  1. First find the last digit of given number (calculating the remainder by dividing the number by 10).
  2. Now multiply the variable reverse by 10 and add the calculated remainder of previous step.
  3. Remove the last digit from the number by dividing the number by 10.
  4. Repeat the above 3 steps inside while loop until the number become 0.

Let’s see the complete logic to calculate the reverse of a given number,

Solution

ReverseNumber.java

package com.javacodepoint.programs;

import java.util.Scanner;

public class ReverseNumber {

	public static void main(String[] args) {

		// Taking input from the user to reverse
		
		System.out.print("Enter an integer number:");

		// Reading user input using Scanner object
		int number = new Scanner(System.in).nextInt();
		
		//Initiating reverse variable with 0 
		int reverse = 0;
		int tempNumber = number;
		
		// while loop will continue until the number become 0
		while(number > 0) {
			
			//Finding the last digit of the number
			int remainder = number % 10;
			
			//Calculating the reverse by multiplying it with 10 and adding remainder (last digit) 
			reverse = reverse * 10 + remainder;
			
			//Removing the last digit from the number
			number = number / 10;
		}
		
		System.out.print("The reverse of the given number is = "+reverse);

	}

}

OUTPUT:

Enter an integer number: 12345
The reverse of the given number is = 54321

Check Palindrome number

A Palindrome number is a special type of number. After reversing a number, if the number will be the same as the original number then that number will be called a Palindrome number.

For example, some Palindrome number is as follow:

121, 242, 12321, 515, 8448, 2345432, etc.

Let’s see the logic to check whether a given number is a Palindrome number or not,

Solution

CheckPalindromeNumber.java

package com.javacodepoint.programs;

import java.util.Scanner;

public class CheckPalindromeNumber {

	public static void main(String[] args) {
		
		// Taking input from the user to check Palindrome number

		System.out.print("Enter an integer number:");

		// Reading user input using Scanner object
		int number = new Scanner(System.in).nextInt();
		
		// Calling method to check Palindrome
		if(isPalindromeNumber(number)) {
			System.out.print("The given number is a Palindrome number.");
		}else {
			System.out.print("The given number is not a Palindrome number.");
		}

	}
	
	/*
	 * Method to check number is Palindrome number or not
	 */
	public static boolean isPalindromeNumber(int number) {
		int remainder, reverse=0;      
        
		//Storing number into a temporary variable  
        int temp = number;      
          
        //Reversing the number  
        while(number > 0){
        	//calculating remainder
        	remainder = number % 10;  
        	
        	//calculate reverse of the number when loop ends.
        	reverse = (reverse*10) + remainder;
        	
        	//removing last digit from the number
            number = number/10;      
        }   
  
        //Checking whether the reversing number is equal to the number or not  
        if(temp == reverse) {
        	return true;
        }
        return false;
	}

}

OUTPUT #1:

Enter an integer number:121
The given number is a Palindrome number.

OUTPUT #2:

Enter an integer number:123
The given number is not a Palindrome number.

Swap two numbers

Swapping two numbers can be also known as exchanging the numbers between two variables. The swapping of two numbers without using a third variable or a temporary variable can be done by following the below simple steps:

For example, let’s take two numbers x=20 (first variable) and y=30 (second variable),

  1. Add both number (x+y) and store it in first variable (x). ie x = x + y
  2. Now Substract the second number from the first, and store it in y variable. ie. y = x – y
  3. Now to the step two again but store the value in x variable. ie. x = x – y

Let’s see the calculation steps:

x = x + y => x = 20 + 30 => 50
y = x – y => y = 50 – 20 => 30
x = x – y => x = 50 – 30 => 20

Let’s see the logic to do the same,

Solution

SwapTwoNumbers.java

package com.javacodepoint.programs;

public class SwapTwoNumbers {

	public static void main(String[] args) {
		
		//Initiating two integer numbers
		
		int x = 20, y=30;
		
		//Print both number before swapping
		System.out.println("x = "+x+", y= "+y);
		
		//Logic to swap these numbers without using a third variable
		
		x = x + y;		
		y = x - y;		
		x = x - y;
		
		//Printing the both number again after swapping
		System.out.println("x = "+x+", y= "+y);

	}

}

OUTPUT:

x = 20, y= 30
x = 30, y= 20

Summary

In this article, you have seen the basic logical programs which are commonly asked in interviews by the interviewer.

Hope you like it. If you have any doubts or questions about the above programs you can ask by writing in the comment below.

Java logical programs list

Java Basic Programs

  1. Java Hello world program
  2. Java Program to Add two Numbers
  3. Java Program to Subtract two Numbers
  4. Java Program to Multiply two Numbers
  5. Java Program to Check Whether a Number is Even or Odd.
  6. Check whether a character is a Vowel or Consonant.
  7. Java Program to find Average of Two Numbers
  8. Java Program to find Average of Three Numbers
  9. Java Program to find the Area of Square
  10. Java Program to Calculate Simple Interest
  11. Java Program to Calculate Compound Interest
  12. List of basic logical programs in Java
  13. How to print a Fibonacci series up to a given number in Java?
  14. How to calculate the factorial of a given number in java?
  15. How to check whether an integer number is a prime number or not in java?
  16. How to check whether a number is a perfect number or not in java?
  17. How to check whether a number is an Armstrong number or not in java?
  18. How to reverse a number in Java?
  19. How to check whether a number is a Palindrome number or not in Java?
  20. How to swap two numbers without using a third variable in Java?
  21. How to reverse a string without using the reverse() method in java?
  22. How to check whether a String is a Palindrome or not in java?
  23. How to count characters from the string in java?
  24. How to check if two strings are anagrams of each other?
  25. How to count the occurrence of the given character in a string in java?
  26. How to swap two strings without using the third variable in java?

Java Pattern Printing Programs

  1. Star pattern programs [Tricks] in Java
  2. Top 30-star pattern programs in java
  3. Top 10 Number pattern programs in java
  4. Top 10 Character pattern programs in java
  5. Top 50 Pattern printing programs in java
  6. Pyramid Pattern.
  7. Diamond Pattern.
  8. Hollow Diamond Pattern.

Java Series Printing Programs

  1. Print a Fibonacci series
  2. Even Numbers Series
  3. Odd Numbers Series
  4. Square Numbers Series
  5. Cube Numbers Series
  6. Print Series 1,2,9,28,65
  7. Java Program to Print Series 1,2,5,10,17
  8. Java Program to Print Series 2,4,8,16,32

Java Array-Based Programs

  1. Copy an Array
  2. Merge Two Arrays.
  3. Sum of Two Arrays.
  4. Print Odd/Even No. from an Array.
  5. Find the Sum of an Array
  6. Sum of Even Numbers in an Array.
  7. Average of Odd/Even Numbers in Array.
  8. Calculate Average Using Array
  9. Find the Smallest Number in an Array.
  10. Find the Largest Number in an Array.
  11. 2nd Largest Number in an Array.
  12. Remove duplicate elements in an Array.

Multi-Dimensional Array Programs

  1. Print Matrix or 2D Array.
  2. Read a Matrix from the User.
  3. Add the Two Matrices.
  4. Subtract the Two Matrices.
  5. Matrix Multiplication.
  6. Identity Matrix Program.
  7. Symmetric Matrix Program.
  8. Find the Transpose of a Matrix.
  9. Find the Smallest Element in a Matrix.
  10. Find the Largest Element in a Matrix.
  11. Search Matrix.
  12. The sum of Diagonals of a Matrix.

Java String Programs

  1. String length without using length() method.
  2. Count the Number of Vowels in a String.
  3. Swap two strings without using the third variable.
  4. Reverse a string without using the reverse() method.
  5. Reverse the words in a given string sentence
  6. Check whether a String is a Palindrome or not in Java.
  7. Count characters from the string in Java.
  8. Count the number of words in the String.
  9. Check if the two strings are anagrams of each other.
  10. Count the occurrence of the given character in a string.
  11. Find the Maximum Occurring Character in a String
  12. Find the First non-repeating Character in a given String
  13. Remove all Duplicates from a given String
  14. Remove a given character from the String
  15. Find the Sum of Digits in a String.
  16. Compare two Strings in Java.
  17. String Permutations Program in Java
  18. Combinations of String in Java

Java Conversion Programs

  1. Binary to Decimal
  2. Binary to Decimal using Recursion
  3. Decimal to Binary
  4. Decimal to Octal
  5. Decimal to Hexadecimal
  6. Fahrenheit to Celsius
  7. Celsius to Fahrenheit

Java Miscellaneous Programs

  1. Generate Random String in Java
  2. Generating Random Numbers in Java
  3. Generating OTP in Java
  4. Secret Message Program in Java

Java Game Programs

  1. Tic-Tac-Toe Game in Java
  2. Hangman Game in Java
  3. Rock Paper Scissors Game in Java
  4. Number Guessing Game in Java
  5. Word Search Solver Game in Java
  6. Tower of Hanoi Game in Java

Java Programs based on the Collection Framework

  1. ArrayList Manipulation: add, remove Elements, find size
  2. Write a Java program to reverse a List without using the built-in Collections.reverse() method.
  3. Find duplicate elements in an ArrayList
  4. Implement a Java program to sort an ArrayList of integer numbers.
  5. Implement a Java program to sort an ArrayList of custom objects based on a specific attribute.
  6. Create a stack using an ArrayList and implement push, pop, and peek operations.
  7. Convert an ArrayList of strings into a string array.
  8. Write a Java program to remove all elements from an ArrayList that are greater than a certain value.
  9. Write a Java program to remove duplicates from an ArrayList while preserving the original order.
  10. Write a Java program to find the common elements in two given ArrayLists.
  11. ArrayList partition into two separate lists of odd/even numbers.
  12. Write a program that extracts a sublist from an ArrayList, given a start and end index.
  13. Merge two sorted ArrayLists into a single sorted ArrayList.
  14. Find unique string in ArrayList with its frequency
  15. Write a program to swap the positions of two elements in an ArrayList given their indices.
  16. Write a program to Create a Custom LinkedList in Java
  17. Write a Java program for Basic Queue Implementation using LinkedList
  18. Write a Java program to create a PriorityQueue to manage a to-do list

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