How To Convert Octal To Decimal In Java

Octal and decimal are two different number systems used in programming. Octal is a base-8 number system, which uses only 8 digits (0-7) to represent numbers. Decimal, on the other hand, is a base-10 number system that uses 10 digits (0-9) to represent numbers. When working with code that uses octal numbers, it may be necessary to convert them to decimals to perform arithmetic operations or for compatibility with modern systems.

Whenever programmers develop an application, he or she has to consider the requirements of the users and generate the output of the data that connects the users. Hence, whenever data is displayed to the users it should be generated in the form of general standards that are used every day.

Binary, octal, and other numerical data representations are irrelevant for non-tech users. Only decimal is the decimal form that is standardized in the real world. Hence, whenever a programmer has an octal form of data representation, he or she has to convert it into decimals for a standardized representation of the data. In this guide, programmers will cover how to convert octal to decimal in Java, including the steps involved and some code examples.

Why There Is A Need to convert Octal To Decimal In Java

In Java, octal and decimal are two different number systems that represent numbers in a different base. Octal is a base-8 number system, which uses only 8 digits to represent numbers (0, 1, 2, 3, 4, 5, 6, 7). On the other hand, decimal is a base-10 number system that uses 10 digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) to represent numbers.

There are several reasons why one might need to convert an octal number to a decimal in Java. Some of these reasons include:

Working with legacy code: Octal was commonly used in older programming languages and systems, and some legacy code still uses octal notation. When working with this code, it may be necessary to convert octal numbers to decimals so that they can be used in modern systems.

Input from users: Some users may enter numbers in octal notation, especially if they are used to working with systems that use octal. If your program is designed to work with decimal numbers, you may need to convert these inputs to decimals before performing calculations.

Converting between number systems: Converting between number systems is a common operation in computer science and engineering. If you are working on a program that requires such conversions, you may need to convert octal numbers to decimals (or vice versa) as part of your implementation.

Arithmetic operations: When performing arithmetic operations with octal numbers, it may be necessary to convert them to decimals first. For example, if you want to add two octal numbers, you need to convert them to decimal, perform the addition, and then convert the result back to octal.

Overall, converting octal numbers to decimals is a common task in programming, and it’s important to understand how to do it in Java in order to work with different types of data and systems.

Different Approaches To Convert Octal to Decimal in Java

There are several different approaches to converting octal to decimal in Java, depending on the requirements of the program and the specific implementation. These approaches are simple and efficient and are suitable for most applications.

1. Using parseInt() and toString()
2. Using loops and mathematical operations
3. Using recursion

Ultimately, the choice of approach will depend on the specific requirements and constraints of the program, as well as the preferences and experience of the developer.

Approach 1 : Convert octal to a decimal using parseInt() and toString()

In this approach, we use parseInt() and toString() methods for the conversion. This method first converts a string into integer type, then convert the integer to decimal. This is how user input is converted into decimals.

Sample code :

// Octal number as a string
String octalNumber = "752";

// Parse the octal string to an integer value
int decimalNumber = Integer.parseInt(octalNumber, 8);

// Convert the decimal integer to a string
String decimalString = Integer.toString(decimalNumber);

// Print the result
System.out.println("Octal number " + octalNumber + " converted to decimal is " + decimalString);

Output :

Octal number 752 converted to decimal is 490

Code Explanation :

1. First, define the octal number as a string “752”.
2. Then use the parseInt() method from the Integer class to parse the octal string into an integer value. The second argument to parseInt() specifies the radix or base of the number system being used, which in this case is 8 for octal.
3. Next, use the toString() method from the Integer class to convert the decimal integer value to a string.
4. Finally, print out the result using the System.out.println() method.

Approach 2 : Convert the octal data to decimal in Java using loops and mathematical operations

In computer science, many problems can be solved using logic. Logics are built by programmers using particular programming languages to solve the computational equation. Programmers can convert octal t decimal by building their own program using loops and mathematical operations. In mathematics, an octal number is converted into a decimal by multiplying each digit by its corresponding power of 8. Then all the results are added to obtain the decimal value of the octal digit. This can be a complex method, but still relevant for competition programming. Let us dip-dive with sample code and explanation.

Sample Code :

// Octal number as a string
String octalNumber = "752";

// Initialize decimal value to 0
int decimalNumber = 0;

// Iterate through each digit of the octal number, starting from the least significant digit
for (int i = 0; i < octalNumber.length(); i++) {
    // Get the digit at the current position
    int digit = Integer.parseInt(String.valueOf(octalNumber.charAt(i)));
    // Multiply the digit by its corresponding power of 8 and add to the decimal value
    decimalNumber += digit * Math.pow(8, octalNumber.length() - 1 - i);
}

// Print the result
System.out.println("Octal number " + octalNumber + " converted to decimal is " + decimalNumber);

Output :

Octal number 752 converted to decimal is 490

Code Explanation :

1. First, define the octal number as a string “752”.
2. Initialize the decimal value to 0, which will gradually build up as code converts each digit of the octal number.
3. Use a for loop to iterate through each digit of the octal number, starting from the least significant digit.
4. Within the loop, use the parseInt() method to get the integer value of the digit at the current position.
5. Then multiply the digit by its corresponding power of 8 (based on its position) and add the result to the decimal value.
6. Finally, print out the result using the System.out.println() method.

Approach 3 : Java code to convert octal value to decimal using recursion

A third approach to converting octal to decimal in Java is to use recursion. This involves breaking the octal number down into smaller sub-problems, recursively converting each sub-problem to decimal, and then combining the results to get the final decimal value. This approach can be elegant and efficient for certain types of problems, but may be more difficult to implement and understand than the other approaches.

Sample code :

// Recursive function to convert octal to decimal
public static int octalToDecimal(String octalNumber, int power) {
    // Base case: if the octal number is empty or the power becomes negative
    if (octalNumber.isEmpty() || power < 0) {
        return 0;
    }
    // Get the most significant digit of the octal number and convert to an integer
    int digit = Integer.parseInt(String.valueOf(octalNumber.charAt(0)));
    // Remove the most significant digit from the octal number string
    String subOctalNumber = octalNumber.substring(1);
    // Calculate the decimal value of the current digit and add to the result
    int result = digit * (int) Math.pow(8, power) + octalToDecimal(subOctalNumber, power - 1);
    return result;
}

// Driver code to test the recursive function
public static void main(String[] args) {
    // Octal number as a string
    String octalNumber = "752";
    // Call the recursive function to convert octal to decimal
    int decimalNumber = octalToDecimal(octalNumber, octalNumber.length() - 1);
    // Print the result
    System.out.println("Octal number " + octalNumber + " converted to decimal is " + decimalNumber);
}

Output :

Octal number 752 converted to decimal is 490

Code explanation :

1. First, define a recursive function octalToDecimal() that takes two arguments – the octal number as a string and the current power of 8 being used.
2. In the function, first check for the base case – if the octal number is empty or the power becomes negative, we return 0.
3. Next, get the most significant digit of the octal number and convert it to an integer.
4. Remove the most significant digit from the octal number string by using the substring() method.
5. Then calculate the decimal value of the current digit using the formula digit * 8^power and add it to the result.
6. Finally, call the octalToDecimal() function recursively with the remaining sub-octal number and the next lower power of 8, until reaching the base case.
7. In the main() function, define the octal number as a string “752” and call the octalToDecimal() function with the initial power of 8 as the length of the octal number – 1.
8. Then print out the result using the System.out.println() method.

Best Approach Out Of Three For Converting Octal Into Decimal

Program used the built-in parseInt() and toString() methods to convert an octal number to decimal is the best approach. This approach is simple and efficient and is suitable for most applications. Below are the statements to support the argument: 

1. Simplicity: Using parseInt() and toString() is a very simple and straightforward way to convert octal to decimal. It involves only a few lines of code and requires minimal mathematical operations.
2. Built-in methods: parseInt() and toString() are built-in methods in Java, which means they are reliable, efficient, and widely used by developers. They are part of the standard Java libraries and have been optimized over time to provide fast and accurate results.
3. Type conversion: parseInt() and toString() allow for easy type conversion between octal and decimal numbers. By simply passing the octal number as a string argument to parseInt(), this can convert it to a decimal integer. Similarly, by passing the decimal integer as an argument to toString(), this can convert it back to a string representation of the decimal number.
4. Error handling: parseInt() provides error handling for cases where the input string is not a valid octal number. It throws a NumberFormatException if the string contains non-octal characters or is too large to be represented as an integer. This helps to ensure the accuracy and reliability of the conversion process.
5. Flexibility: parseInt() and toString() allow for flexible input and output formats. The programmer can pass the octal number as a string with or without the leading “0” prefix, and he or she can choose the output format of the decimal number by specifying the number of decimal places in toString().

Overall, using parseInt() and toString() is a simple, reliable, and efficient way to convert octal to decimal in Java. It provides a flexible and error-free conversion process that is widely used and accepted by developers.

The choice of approach will ultimately be determined by the particular limitations and objectives of the application, as well as the preferences and knowledge of the developer.

Sample Problems

Sample Problem 1

Suppose you are working in a bank, that receives numeric data from various sources. Write a Java program to convert a string taken from the user from octal to decimal using parseInt() and toString(). Then print the decimal value of the string.

Sample code :

// Import the Scanner class to take user input
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Take the user input
        Scanner input = new Scanner(System.in);
        
        System.out.print("Enter an octal number: ");
        String octalNumber = input.nextLine();

        // Parse the octal string to an integer value
        int decimalNumber = Integer.parseInt(octalNumber, 8);

        // Convert the decimal integer to a string
        String decimalString = Integer.toString(decimalNumber);

        // Print the result
        System.out.println("Octal number " + octalNumber + " converted to decimal is " + decimalString);
    }
}

Output :

Enter an octal number: 12
Octal number 12 converted to decimal is 10

Code Explanation :

1. Take the user input using Scanner class.
2. Then use the parseInt() method from the Integer class to parse the octal string into an integer value. The second argument to parseInt() specifies the radix or base of the number system being used, which is 8 for octal.
3. Next, use the toString() method from the Integer class to convert the decimal integer value to a string.
4. Finally, print out the result using the System.out.println() method.

Sample Problem 2

How to convert octal to decimal in Java using the loops and mathematical operations? If you want to display the weight of the item, Write a Java program to take the input as the height of the student which is in octal value and convert it to decimal, and print the resulting decimal value.

Sample Code :

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Take the user input
        Scanner input = new Scanner(System.in);
        
        System.out.print("Enter an octal number: ");
        String octalNumber = input.nextLine();

        // Initialize decimal value to 0
        int decimalNumber = 0;

        // Iterate through each digit of the octal number, starting from the least significant digit
        for (int i = 0; i < octalNumber.length(); i++) {
            // Get the digit at the current position
            int digit = Integer.parseInt(String.valueOf(octalNumber.charAt(i)));
            // Multiply the digit by its corresponding power of 8 and add to the decimal value
            decimalNumber += digit * Math.pow(8, octalNumber.length() - 1 - i);
        }

        // Print the result
        System.out.println("Octal number " + octalNumber + " converted to decimal is " + decimalNumber);
    }
}

Output :

Enter an octal number: 78
Octal number 78 converted to decimal is 64

Code Explanation :

1. Take the user input from Scanner class.
2. Initialize the decimal value to 0, which will gradually build up as code converts each digit of the octal number.
3. Use a for loop to iterate through each digit of the octal number, starting from the least significant digit.
4. Within the loop, use the parseInt() method to get the integer value of the digit at the current position.
5. Then multiply the digit by its corresponding power of 8 (based on its position) and add the result to the decimal value.
6. Finally, print out the result using the System.out.println() method.

Sample Problem 3

How to convert octal to decimal in Java using recursion. Create a program to take the total amount paid by the user and convert it into decimals and display the result.

Sample code :

import java.util.Scanner;

public class Main {
    // Recursive function to convert octal to decimal
    public static int octalToDecimal(String octalNumber, int power) {
        // Base case: if the octal number is empty or the power becomes negative
        if (octalNumber.isEmpty() || power < 0) {
            return 0;
        }
        // Get the most significant digit of the octal number and convert to an integer
        int digit = Integer.parseInt(String.valueOf(octalNumber.charAt(0)));
        // Remove the most significant digit from the octal number string
        String subOctalNumber = octalNumber.substring(1);
        // Calculate the decimal value of the current digit and add to the result
        int result = digit * (int) Math.pow(8, power) + octalToDecimal(subOctalNumber, power - 1);
        return result;
    }

    // Driver code to test the recursive function
    public static void main(String[] args) {
        // Take the user input
        Scanner input = new Scanner(System.in);
        System.out.print("Enter an octal number: ");
        String octalNumber = input.nextLine();

        // Call the recursive function to convert octal to decimal
        int decimalNumber = octalToDecimal(octalNumber, octalNumber.length() - 1);
        // Print the result
        System.out.println("Octal number " + octalNumber + " converted to decimal is " + decimalNumber);
    }
}

Output :

Enter an octal number: 25
Octal number 25 converted to decimal is 21

Code explanation :

1. First, define a recursive function octalToDecimal() that takes two arguments – the octal number as a string and the current power of 8 being used.
2. In the function, first check for the base case – if the octal number is empty or the power becomes negative, we return 0.
3. Next, get the most significant digit of the octal number and convert it to an integer.
4. Remove the most significant digit from the octal number string by using the substring() method.
5. Then calculate the decimal value of the current digit using the formula digit * 8^power and add it to the result.
6. Finally, call the octalToDecimal() function recursively with the remaining sub-octal number and the next lower power of 8, until reaching the base case.
7. In the main() function, define the octal number as a string “675” and call the octalToDecimal() function with the initial power of 8 as the length of the octal number – 1.
8. Then print out the result using the System.out.println() method.

Conclusion

Decimal is used to represent real-life measures like weight, length, money, etc. Hence, while developing applications, programmers have to represent the values according to common standards.  Hence, it becomes necessary to convert octal data into decimals. The basic difference between both is that decimals have a base of 8 (0-7) and decimals have a base of (0-9).

Three approaches are discussed to convert octal into decimals. The first one is through pre-defined Java methods. parseInt() and toString() methods are considered the best approach due to their simplicity, built-in error handling, and flexibility.

Another one is through mathematical operations, which can be complex and need logic building. This technique can be irrelevant for beginners and non-maths background programmers. These approaches require more advanced knowledge of Java programming and may require more lines of code to implement. Still, they offer greater flexibility and customization options to developers.